Faculty Profiles - Nakai Mitsuo

Papers - Nakai Mitsuo

Division display >> ／ All the affair displays 1 - 304 of about 304

Second harmonic generation of focused beams on the LFEX laser facility Reviewed International journal

Y. Arikawa, Z. Hu, K. Tsubakimoto, A. Morace, R. Takizawa, H. Shiraga, M. Nakai, T. Pikuz, A. Martynenko, N. Iwata, Y. Sentoku, M. Hata, S. Kojima, T. Johzaki, Y. Nakata, S. Fujioka, A. Yogo, R. Kodama

Optics Express 32 ( 16 ) 28390 - 28401 2024.7

There is a strong demand for efficient second harmonic generation (SHG) in ultra-intense short-pulse lasers. This paper demonstrates the generation of an unconverted fundamental and second harmonics mixed laser on the LFEX laser system. The LFEX laser beams with four-beams combined energy of 222 J and a pulse duration of 1.5 ps, is successfully converted to 102 J of 2ω light and 100 J of unconverted 1ω light utilizing 0.5 mm-thick LBO crystal plates in a focusing beams implemented after an off-axis parabola.
Verification of successful SHG is confirmed through X-ray pinhole imaging and electron spectrometry. This novel technique is not limited to LFEX lasers and holds applicability for various ultra-intense lasers. Consequently, this accomplishment significantly contributes to expanding the capability for high-energy density laser-plasma experiments.

Cryogenic solid deuterium target formation to realize highly pure deuteron acceleration by high-intensity laser Reviewed International journal

T. Wei, A. Iwamoto, Z. Lan, T. Hayakawa, Y. Arikawa, D. Tanabe, T. Ishimoto, T. Mori, M.Takeshita, M. Murakami, Y. Gu, A. Morace, M. Nakai, A. Yogo

Japanese Journal of Applied Physics 63 ( 4 ) 046002 - 046002 2024.4

In recent years, laser-driven neutron sources have attracted attention for their applications such as nondestructive analysis and the production of medical radioisotopes. One of the efficient neutron production methods is the use of the ⁹Be(d, n)¹⁰B reaction on a beryllium target with deuterons accelerated by laser–plasma interactions, since this is an exothermic reaction. For efficient deuteron acceleration, we have developed a formation system for solid deuterium targets. A millimeter thick solid deuterium target can be formed with the system. Before the laser shot, the solid deuterium target in the laser chamber can be mechanically moved to the laser irradiation point. We have demonstrated deuteron acceleration by the LFEX laser, and a highly pure deuteron pulse with energies of up to 6.2 MeV was measured with a Thomson parabola ion spectrometer.

The elements of a small debris mitigation system using spaceborne laser International coauthorship

Shigeaki Uchida, Kotomi Kawakami, Hideki Okamura, Nakai Mitsuo , Kazunori Shibata, Xiao Xiao (, Yin Danqing , Keke Zhang, Zhonghao Heng

2nd International Orbital Debris Conference Papers 2023 2023.12

Demonstration of efficient relativistic electron acceleration by surface plasmonics with sequential target processing using high repetition lasers

Yasunobu Arikawa, Alessio Morace, Yuki Abe, Natsumi Iwata, Yasuhiko Sentoku, Akifumi Yogo, Kazuki Matsuo, Mitsuo Nakai, Hideo Nagatomo, Kunioki Mima, Hiroaki Nishimura, Shinsuke Fujioka, Ryosuke Kodama, Shunsuke Inoue, Masaki Hashida, Shuji Sakabe, Diego De Luis, Giancarlo Gatti, Marine Huault, José Antonio Pérez-Hernández, Luis Roso, Luca Volpe

Physical Review Research 5 ( 1 ) 2023.1

Laser-Driven Neutron Generation Realizing Single-Shot Resonance Spectroscopy Reviewed International coauthorship International journal

A. Yogo, Z. Lan, Y. Arikawa, Y. Abe, S. R. Mirfayzi, T. Wei, T. Mori, D. Golovin, T. Hayakawa, N. Iwata, S. Fujioka, M. Nakai, Y. Sentoku, K. Mima, M. Murakami, M. Koizumi, F. Ito, J. Lee, T. Takahashi, K. Hironaka, S. Kar, H. Nishimura, R. Kodama

Physical Review X 13 ( 1 ) 011011-1 - 011011-12 2023.1

Feasibility study of laser-driven neutron sources for pharmaceutical applications

Takato Mori, Akifumi Yogo, Yasunobu Arikawa, Takehito Hayakawa, Seyed R. Mirfayzi, Zechen Lan, Tianyun Wei, Yuki Abe, Mitsuo Nakai, Kunioki Mima, Hiroaki Nishimura, Shinsuke Fujioka, Ryosuke Kodama

High Power Laser Science and Engineering 2023

We predict the production yield of a medical radioisotope 67Cu using 67Zn(n, p)67Cu and 68Zn(n, pn)67Cu reactions with fast neutrons provided from laser-driven neutron sources (LDNSs). The neutrons were generated by the p+9Be and d+9Be reactions with high energy ions accelerated by laser-plasma interaction. We evaluated the yield to be (3.3±0.5)×105atoms for 67Cu, corresponding to a radioactivity of 1.0±0.2 Bq, for a Zn foil sample with a single laser shot. Using a simulation with this result, we estimated 67Cu production with a high-frequency laser. The result suggests that it is possible to generate 67Cu with a radioactivity of 270 MBq using a future laser system with a frequency of 10 Hz and 10000-s radiation in a hospital.

Super-strong magnetic field-dominated ion beam dynamics in focusing plasma devices

A. Morace, Y. Abe, J. J. Honrubia, N. Iwata, Y. Arikawa, Y. Nakata, T. Johzaki, A. Yogo, Y. Sentoku, K. Mima, T. Ma, D. Mariscal, H. Sakagami, T. Norimatsu, K. Tsubakimoto, J. Kawanaka, S. Tokita, N. Miyanaga, H. Shiraga, Y. Sakawa, M. Nakai, H. Azechi, S. Fujioka, R. Kodama

Scientific Reports 12 ( 1 ) 2022.12

Abstract

High energy density physics is the field of physics dedicated to the study of matter and plasmas in extreme conditions of temperature, densities and pressures. It encompasses multiple disciplines such as material science, planetary science, laboratory and astrophysical plasma science. For the latter, high energy density states can be accompanied by extreme radiation environments and super-strong magnetic fields. The creation of high energy density states in the laboratory consists in concentrating/depositing large amounts of energy in a reduced mass, typically solid material sample or dense plasma, over a time shorter than the typical timescales of heat conduction and hydrodynamic expansion. Laser-generated, high current–density ion beams constitute an important tool for the creation of high energy density states in the laboratory. Focusing plasma devices, such as cone-targets are necessary in order to focus and direct these intense beams towards the heating sample or dense plasma, while protecting the proton generation foil from the harsh environments typical of an integrated high-power laser experiment. A full understanding of the ion beam dynamics in focusing devices is therefore necessary in order to properly design and interpret the numerous experiments in the field. In this work, we report a detailed investigation of large-scale, kilojoule-class laser-generated ion beam dynamics in focusing devices and we demonstrate that high-brilliance ion beams compress magnetic fields to amplitudes exceeding tens of kilo-Tesla, which in turn play a dominant role in the focusing process, resulting either in a worsening or enhancement of focusing capabilities depending on the target geometry.

NMR Spectroscopy for Proof-of-Concept Experimentation on a Polarized Laser Fusion Process

Masahiko Utsuro, Mitsuo Nakai, Hideki Kohri, Takeshi Ohta, Takumi Konno, Asako Igashira, Mamoru Fujiwara

Fusion Science and Technology 78 ( 7 ) 513 - 527 2022.10

Predictive capability of material screening by fast neutron activation analysis using laser-driven neutron sources

Y. Abe, A. Nakao, Y. Arikawa, A. Morace, T. Mori, Z. Lan, T. Wei, S. Asano, T. Minami, Y. Kuramitsu, H. Habara, H. Shiraga, S. Fujioka, M. Nakai, A. Yogo

Review of Scientific Instruments 93 ( 9 ) 2022.9

Bright, short-pulsed neutron beams from laser-driven neutron sources (LANSs) provide a new perspective on material screening via fast neutron activation analysis (FNAA). FNAA is a nondestructive technique for determining material elemental composition based on nuclear excitation by fast neutron bombardment and subsequent spectral analysis of prompt γ-rays emitted by the active nuclei. Our recent experiments and simulations have shown that activation analysis can be used in practice with modest neutron fluences on the order of 105 n/cm2, which is available with current laser technology. In addition, time-resolved γ-ray measurements combined with picosecond neutron probes from LANSs are effective in mitigating the issue of spectral interference between elements, enabling highly accurate screening of complex samples containing many elements. This paper describes the predictive capability of LANS-based activation analysis based on experimental demonstrations and spectral calculations with Monte Carlo simulations.

Picosecond snapshot imaging of electric fields induced on a cone guide target designed for fast ignition scenario Reviewed

Binghe Shi, Akifumi Yogo, Kazuki Okamoto, Daniil Golovin, Seyed Reza Mirfayzi, Alessio Morace, Yasunobu Arikawa, Kohei Yamanoi, Yuki Abe, Masakatsu Murakami, Yanjun Gu, Kunioki Mima, Yasuhiko Sentoku, Mitsuo Nakai, Hiroyuki Nishimura, Hiroyuki Shiraga, Shinsuke Fujioka, Tomoyuki Johzaki, Akifumi Iwamoto, Hitoshi Sakagami, Ryosuke Kodama

Journal of Plasma Physics 88 ( 4 ) 905880404 2022.8

In this study, we experimentally evaluate the ion transportation through a cone guide target, which accelerates ions up to MeV energies via target normal sheath acceleration, and transports them onto the position of imploding fuel in the fast ignition scenario of nuclear fusion. We measured the electric and magnetic fields (EM-fields) induced by return current streaming along the cone wall by proton radiography, and we report that the EM-fields are predominantly induced within a temporal window up to 30 ps after the laser injection. The magnitude of the electric field is maximized around 13 ps, reaching $4.0\times 10^{10} \mathrm {V}\ \mathrm {m}^{-1}$, when the magnetic field is below 200 T. The present scheme provides insights on the EM-fields evaluation in the time region that is difficult to treat with simulations due to the computing resources.

Thermal neutron fluence measurement using a cadmium differential method at the laser-driven neutron source

Takato Mori, Akifumi Yogo, Takehito Hayakawa, Seyed R. Mirfayzi, Zechen Lan, Tianyun Wei, Yuki Abe, Yasunobu Arikawa, Mitsuo Nakai, Kunioki Mima, Hiroaki Nishimura, Shinsuke Fujioka, Ryosuke Kodama

Journal of Physics G: Nuclear and Particle Physics 49 ( 6 ) 2022.6

We produced high-energy neutrons by p + Be and d + Be reactions with protons and deuterons with continuous energies of up to 30 and 10 MeV/u, respectively, provided from laser-plasma interactions. Thermal neutrons were subsequently generated through deceleration by a small moderator with conjunction on the Be target. Here, we report the measurements on the thermal neutron fluence using the activation method with/without Cd filters. The unstable isotopes of 198Au, 56Mn, 60Co, and 181Hf were produced through (n, γ) reactions by a single laser shot. The nuclear reaction fractions were evaluated by measuring the γ-rays emitted from these unstable isotopes. The thermal neutron fluences from the four nuclides are consistent within their experimental uncertainties. The fluence is evaluated to be (2.2 ± 0.4) × 105 neutrons cm-2 at the distance of approximately 9 mm at 90° against the laser axis. The present result shows that the method to generate thermal neutrons from a compact neutron source with a diameter of 44 mm and length of 46 mm is expected to be a useful tool for various nuclear experiments and applications.

Non-destructive inspection of water or high-pressure hydrogen gas in metal pipes by the flash of neutrons and x rays generated by laser

Tianyun Wei, Akifumi Yogo, Takehito Hayakawa, Yasunobu Arikawa, Yuki Abe, Maiko Nakanishi, Seyed Reza Mirfayzi, Zechen Lan, Takato Mori, Kunioki Mima, Shinsuke Fujioka, Masakatsu Murakami, Mitsuo Nakai, Hiroaki Nishimura, Satyabrata Kar, Ryosuke Kodama

AIP Advances 12 ( 4 ) 045220 - 045220 2022.4

The thermal and epithermal neutrons are powerful probes to inspect water or high-pressure hydrogen gas because of their large scattering cross-sections with protons. Laser-driven neutron source, which is able to simultaneously emit different types of radiations such as x rays, can be used for neutron and x-ray radiography in the same laser shot. In this paper, we report the demonstration of non-destructive inspection for H2O contained within a stainless steel pipe using a laser-driven thermal neutron source, where water and stainless containers are detected by neutrons and x rays, respectively. The simulation result indicates that this method can also provide the capability to measure the hydrogen density in high-pressure hydrogen gas in metal containers.

Author Correction: Proof-of-principle experiment for laser-driven cold neutron source (Scientific Reports, (2020), 10, 1, (20157), 10.1038/s41598-020-77086-y)

S. R. Mirfayzi, A. Yogo, Z. Lan, T. Ishimoto, A. Iwamoto, M. Nagata, M. Nakai, Y. Arikawa, Y. Abe, D. Golovin, Y. Honoki, T. Mori, K. Okamoto, S. Shokita, D. Neely, S. Fujioka, K. Mima, H. Nishimura, S. Kar, R. Kodama

Scientific Reports 11 ( 1 ) 2021.12

The original version of this Article contained errors. In Figure 3b, where “Deutron” now reads: “Deuteron” In addition, in Figure 4d, where the x-axis “10–4, 10– 3, 10– 2, 10– 1, 10, 102, 103” now reads: “10–4, 10– 3, 10– 2, 10– 1, 1, 101, 102” The original Figures 3 and 4 and accompanying legends appear below. Finally, the Author Contributions section, “The moderator and experiment was developed by S.R.M. with support from A.I. and funded by A.Y. to and led by S.R.M. S.R.M., A.Y., Z.L. and T.I. executed the experiment with support from, AI, KM, MNag, MNak, YAr, YAb, D.G., Y.H., T.M., S.S. and K.O. contributed both to the experimental setup and diagnostics. S.R.M. and Z.L., T.I. performed data analysis.” now reads: “The moderator and experiment were developed by S.R.M. with support from A.I. The experiment funded by A.Y. and led by S.R.M. S.R.M., A.Y., Z.L. and T.I. executed the experiment with support from A.I., K.M., M.Nag, M.Nak, Y.Ar., Y.Ab., D.G., Y.H., T.M., S.S. and K. contributed both to the experimental setup and diagnostics. S.R.M., Z.L. and T.I. performed the data analysis. The manuscript was prepared by S.R.M., D.N., S.F., K.M., H.N., S.K. and R.K. were involved in discussions and preparation.” The original Article has been corrected. (Figure presented.).

Preliminary Cryogenic Layering by the Infrared Heating Method Modified with Cone Temperature Control for the Polystyrene Shell FIREX Target

Keisuke IWANO, Akifumi IWAMOTO, Kohei YAMANOI, Yasunobu ARIKAWA, Hideo NAGATOMO, Mitsuo NAKAI, Takayoshi NORIMATSU

Plasma and Fusion Research 16 1404099 - 1404099 2021.11

Single shot radiography by a bright source of laser-driven thermal neutrons and x-rays

Akifumi Yogo, Seyed Reza Mirfayzi, Yasunobu Arikawa, Yuki Abe, Tianyun Wei, Takato Mori, Zechen Lan, Yuki Hoonoki, Daniil O. Golovin, Keisuke Koga, Yosuke Suzuki, Masato Kanasaki, Shinsuke Fujioka, Mitsuo Nakai, Takehito Hayakawa, Kunioki Mima, Hiroaki Nishimura, Satyabrata Kar, Ryosuke Kodama

APPLIED PHYSICS EXPRESS 14 ( 10 ) 2021.10

Thermal neutron (similar to 25 meV) beam is a powerful tool for investigating the structure and properties of materials used in science and technology. A laser-driven neutron source generating 10(10) neutrons within 1 ns duration is utilized to a single shot radiography with a dual beam of thermal neutrons and X-rays. As a proof of principle, we show the non-destructive inspection of hazardous substances (Cadmium) contained in a typical battery, when the cadmium anode thickness is evaluated from the transmittance of thermal neutrons. The fact that the neutron inspection above is performed with a single laser shot, i.e. with a single bunch of neutrons leads to a safer neutron source that is optically controlled on/off, and provides a novel tool for science and engineering.

Direct evaluation of high neutron density environment using reaction induced by laser-driven neutron source

Takato Mori, Akifumi Yogo, Takehito Hayakawa, Seyed R. Mirfayzi, Zechen Lan, Yuki Abe, Yasunobu Arikawa, Daniil Golovin, Tianyun Wei, Yuki Honoki, Mitsuo Nakai, Kunioki Mima, Hiroaki Nishimura, Shinsuke Fujioka, Ryosuke Kodama

Physical Review C 104 ( 1 ) 2021.7

We demonstrate that reactions are induced by a high-flux pulse of fast neutrons ( neutrons in ) provided from a laser-driven neutron source (LDNS). The maximum energy of the broadband neutrons reaches a few tens MeV. Several kinds of metal targets are exposed to the fast neutrons. As a result, unstable isotopes, such as , and are produced by reactions and , and are produced by reactions. We evaluate the neutron fluence and energy spectrum using the activation method in conjunction with a time-of-flight measurement. The neutron fluence is determined to be in the energy range from approximately 8 to 20 MeV at 8-mm downstream of the neutron source. The present scheme provides a method to evaluate high-density neutrons seen in stellar environments, which are expected to be generated from future LDNSs.

Dosimetric calibration of GafChromic HD-V2, MD-V3, and EBT3 films for dose ranges up to 100 kGy

Y. Abe, A. Morace, Y. Arikawa, S. R. Mirfayzi, D. Golovin, K. F.F. Law, S. Fujioka, A. Yogo, M. Nakai

Review of Scientific Instruments 92 ( 6 ) 2021.6

Surface structure on diamond foils generated by spatially nonuniform laser irradiation Reviewed

Hiroki Kato, Hideo Nagatomo, Mitsuo Nakai, Tatsuhiro Sakaiya, Hidenori Terasaki, Tadashi Kondo, Yoichiro Hironaka, Katsuya Shimizu, Keisuke Shigemori

Scientific Reports 10 ( 1 ) 2020.12

© 2020, The Author(s). Here we report on the effects of material strength factors on the generation of surface structure due to nonuniform laser irradiation. The influence of material strength on the generation of perturbation on a diamond surface subjected to nonuniform laser irradiation was experimentally investigated. Our previous investigations suggested that stiffer and denser materials reduce surface perturbation due to spatially nonuniform laser irradiation, which was reproduced well by calculations with multi-dimensional hydrodynamic simulation code. In this work, we found that local fractures due to yield strength failure are generated by high degrees of irradiation non-uniformity. A characteristic crack-like surface structure was observed, which was not reproduced by the 2D simulation code calculations at all. The 2D simulations showed that the pressure at the diamond surface locally exceeds the Hugoniot elastic limit due to nonuniform irradiation, implying the potential for development of surface perturbations. We also measured the areal-density distribution of perturbations for single-crystal diamond and diamond with a thin high atomic number (high-Z) coating on its surface. The experimental results imply that the combination of a stiff material and thin high-Z coating can suppress the solid-strength effects caused by large irradiation non-uniformity. The knowledge given here is applicable to inertial confinement fusion target design, laser material processing, and universal problems involving solids and high-energy-density plasmas.

Proof-of-principle experiment for laser-driven cold neutron source

S. R. Mirfayzi, A. Yogo, Z. Lan, T. Ishimoto, A. Iwamoto, M. Negata, M. Nakai, Y. Arikawa, Y. Abe, D. Golovin, Y. Honoki, T. Mori, K. Okamoto, S. Shokita, D. Neely, S. Fujioka, K. Mima, H. Nishimura, S. Kar, R. Kodama

SCIENTIFIC REPORTS 10 ( 1 ) 2020.11

The scientific and technical advances continue to support novel discoveries by allowing scientists to acquire new insights into the structure and properties of matter using new tools and sources. Notably, neutrons are among the most valuable sources in providing such a capability. At the Institute of Laser Engineering, Osaka, the first steps are taken towards the development of a table-top laser-driven neutron source, capable of producing a wide range of energies with high brightness and temporal resolution. By employing a pure hydrogen moderator, maintained at cryogenic temperature, a cold neutron (similar to 25 meV) flux of similar to 2 x 10(3) n/cm(2)/pulse was measured at the proximity of the moderator exit surface. The beam duration of hundreds of ns to tens of mu s is evaluated for neutron energies ranging from 100s keV down to meV via Monte-Carlo techniques. Presently, with the upcoming J-EPoCH high repetition rate laser at Osaka University, a cold neutron flux in orders of similar to 1 x 10(9) n/cm(2)/ s is expected to be delivered at the moderator in a compact beamline.

Relativistic magnetic reconnection in laser laboratory for testing an emission mechanism of hard-state black hole system

K. F.F. Law, Y. Abe, A. Morace, Y. Arikawa, S. Sakata, S. Lee, K. Matsuo, H. Morita, Y. Ochiai, C. Liu, A. Yogo, K. Okamoto, D. Golovin, M. Ehret, T. Ozaki, M. Nakai, Y. Sentoku, J. J. Santos, E. D'Humières, Ph Korneev, S. Fujioka

Physical Review E 102 ( 3 ) 2020.9

Magnetic reconnection in a relativistic electron magnetization regime was observed in a laboratory plasma produced by a high-intensity, large energy, picoseconds laser pulse. Magnetic reconnection conditions realized with a laser-driven several kilotesla magnetic field is comparable to that in the accretion disk corona of black hole systems, i.e., Cygnus X-1. We observed particle energy distributions of reconnection outflow jets, which possess a power-law component in a high-energy range. The hardness of the observed spectra could explain the hard-state x-ray emission from accreting black hole systems.

Monte Carlo particle collision model for qualitative analysis of neutron energy spectra from anisotropic inertial confinement fusion Reviewed

Y. Abe, T. Johzaki, A. Sunahara, Y. Arikawa, T. Ozaki, K. Ishii, R. Hanayama, S. Okihara, E. Miura, O. Komeda, S. Sakata, K. Matsuo, H. Morita, R. Takizawa, R. Mizutani, A. Iwamoto, H. Sakagami, Y. Sentoku, H. Shiraga, M. Nakai, S. Fujioka, Y. Mori, Y. Kitagawa

High Energy Density Physics 36 2020.8

© 2020 Elsevier B.V. A Monte Carlo (MC) code simulating the kinetics of two-particle collisions has shown to have certain advantages in the spectral analysis of neutrons from fast-ignition inertial confinement fusion (ICF). The MC code quickly displays neutron spectra produced in the expected fusion plasma kinetics (incl. ion energy spectrum, anisotropy, and collision geometry). This allows to explore various potential mechanisms of neutron production without using time-consuming hydrodynamic or particle simulations and makes it possible to give a feedback to ongoing experiments. The validity of this model was demonstrated in the ”cone-free-shell” fast ignition experiment at the GEKKO-XII - LFEX laser facility, where the model provided a clear explanation for the significant spectral modulation of D(d, n)3He neutrons generated through the interaction between a high-power laser and a long-scale plasma.

The avalanche image intensifier panel for fast neutron radiography by using laser-driven neutron sources

R. Mizutani, Y. Abe, Y. Arikawa, J. Nishibata, A. Yogo, S. R. Mirfayzi, H. Nishimura, K. Mima, S. Fujioka, M. Nakai, H. Shiraga, R. Kodama

High Energy Density Physics 36 2020.8

© 2020 Elsevier B.V. Laser-driven neutrons have been expected as an optimum source for neutron radiography applications. Since the neutron fluence is lower than that of accelerator-based neutron source a new device for amplifying scintillation light has been required. The avalanche image intensifier panel discussed here has a large aperture and fast response which has been developed specifically for laser-driven neutron radiography applications. The gain uniformity for pulsed light sources was improved by optimizing electrical circuit. The performances of the improved image intensifier panel were experimentally evaluated. With the improved circuit, the gain non-uniformity was σ=5% and impulse response was 50 ns in full width half maximum (FWHM), and dynamic range was 100 which is invariable for a light pulse duration from 15 ns to 500 ns. Laser-driven neutron radiography has been successfully demonstrated in spite of the low neutron flux.

The conceptual design of 1-ps time resolution neutron detector for fusion reaction history measurement at OMEGA and the National Ignition Facility Reviewed

Yasunobu Arikawa, Masato Ota, Makoto Nakajima, Tomoki Shimizu, Sadashi Segawa, Thanh Nhat Khoa Phan, Youichi Sakawa, Yuki Abe, Alessio Morace, Seyed Reza Mirfayzi, Akifumi Yogo, Shinsuke Fujioka, Mitsuo Nakai, Hiroyuki Shiraga, Hiroshi Azechi, Ryosuke Kodama, Koichi Kan, Johan Frenje, Maria Gatu Johnson, Arijit Bose, Neel V. Kabadi, Graeme D. Sutcliffe, Patrick Adrian, Chikang Li, Fredrick H. Séguin, Richard Petrasso

The Review of scientific instruments 91 ( 6 ) 063304 2020.6

The nuclear burn history provides critical information about the dynamics of the hot-spot formation and high-density fuel-shell assembly of an Inertial Confinement Fusion (ICF) implosion, as well as information on the impact of alpha heating, and a multitude of implosion failure mechanisms. Having this information is critical for assessing the energy-confinement time τE and performance of an implosion. As the confinement time of an ICF implosion is a few tens of picoseconds, less than 10-ps time resolution is required for an accurate measurement of the nuclear burn history. In this study, we propose a novel 1-ps time-resolution detection scheme based on the Pockels effect. In particular, a conceptual design for the experiment on the National Ignition Facility and OMEGA are elaborated upon herein. A small organic Pockels crystal "DAST" is designed to be positioned ∼5 mm from the ICF implosion, which is scanned by a chirped pulse generated by a femto-second laser transmitted through a polarization-maintained optical fiber. The originally linearly polarized laser is changed to an elliptically polarized laser by the Pockels crystal when exposed to neutrons, and the modulation of the polarization will be analyzed. Our study using 35-MeV electrons showed that the system impulse response is 0.6 ps. The response time is orders of magnitude shorter than current systems. Through measurements of the nuclear burn history with unprecedented time resolution, this system will help for a better understanding of the dynamics of the hot-spot formation, high-density fuel-shell assembly, and the physics of thermonuclear burn wave propagation.

Development of Tritium Tracer Doped Liquid Fuel Target for Inertial Confinement Fusion at the Gekko XII-LFEX Facility

Yasunobu Arikawa, Yuki Iwasa, Kohei Yamanoi, Keisuke Iwano, Shinsuke Fujioka, Akifumi Iwamoto, Mitsuo Nakai, Yuji Hatano, Masanori Hara, Satoshi Akamaru, Takayoshi Norimatsu, Ryosuke Kodama

Fusion Science and Technology 76 ( 4 ) 464 - 470 2020.5

© 2020, © 2020 American Nuclear Society. In inertial confinement fusion (ICF), a fuel target containing deuterium and tritium is used. In recent ICF experiments on the Gekko XII LFEX facility at the Institute of Laser Engineering at Osaka University (ILE-Osaka), a target comprised of a polystyrene capsule filled with D2O liquid and a solution of X-ray tracer materials, such as copper, titanium, or chlorine, was developed. In this study, an additional T2O doping technique by which tritium can be mixed uniformly has been developed. The T2O is synthesized by T2 gas using a CuO oxidation catalyst. The T2O is agglutinated by cold trap and transferred to a target cell in which a D2O-solution-filled target is placed. Because polystyrene is slightly permeable for T2O and D2O, D2O is exchanged by T2O and completely mixed. Thus, a uniform tritium-doped ICF target with various materials can be fabricated. The T2O synthesizing and doping system is developed and tested using H2 as a cold run. The H2O is successfully doped to a D2O prefilled target at approximately 50% doping. This scheme will be utilized in future fast ignition experiments at ILE-Osaka.

Production of relativistic electrons at subrelativistic laser intensities

G. J. Williams, A. Link, M. Sherlock, D. A. Alessi, M. Bowers, A. Conder, P. Di Nicola, G. Fiksel, F. Fiuza, M. Hamamoto, M. R. Hermann, S. Herriot, D. Homoelle, W. Hsing, E. d'Humières, D. Kalantar, A. Kemp, S. Kerr, J. Kim, K. N. LaFortune, J. Lawson, R. Lowe-Webb, T. Ma, D. A. Mariscal, D. Martinez, M. J.-E. Manuel, M. Nakai, L. Pelz, M. Prantil, B. Remington, R. Sigurdsson, C. Widmayer, W. Williams, L. Willingale, R. Zacharias, K. Youngblood, Hui Chen

Physical Review E 101 ( 3 ) 2020.3

Petapascal Pressure Driven by Fast Isochoric Heating with a Multipicosecond Intense Laser Pulse Reviewed

Kazuki Matsuo, Naoki Higashi, Natsumi Iwata, Shohei Sakata, Seungho Lee, Tomoyuki Johzaki, Hiroshi Sawada, Yuki Iwasa, King Fai Farley Law, Hiroki Morita, Yugo Ochiai, Sadaoki Kojima, Yuki Abe, Masayasu Hata, Takayoshi Sano, Hideo Nagatomo, Atsushi Sunahara, Alessio Morace, Akifumi Yogo, Mitsuo Nakai, Hitoshi Sakagami, Tetsuo Ozaki, Kohei Yamanoi, Takayoshi Norimatsu, Yoshiki Nakata, Shigeki Tokita, Junji Kawanaka, Hiroyuki Shiraga, Kunioki Mima, Hiroshi Azechi, Ryosuke Kodama, Yasunobu Arikawa, Yasuhiko Sentoku, Shinsuke Fujioka

Physical Review Letters 20 ( 124 ) 035001-1 - 035001-5 2020.1

Fast isochoric laser heating is a scheme to heat matter with a relativistic intensity (>1018 W/cm2) laser pulse for producing an ultrahigh-energy-density (UHED) state. We have demonstrated an efficient fast isochoric heating of a compressed dense plasma core with a multipicosecond kilojoule-class petawatt laser and an assistance of externally applied kilotesla magnetic fields for guiding fast electrons to the dense plasma. A UHED state of 2.2 PPa is achieved experimentally with 4.6 kJ of total laser energy that is one order of magnitude lower than the energy used in the conventional implosion scheme. A two-dimensional particle-in-cell simulation confirmed that diffusive heating from a laser-plasma interaction zone to the dense plasma plays an essential role to the efficient creation of the UHED state.

Electromagnetic field growth triggering super-ponderomotive electron acceleration during multi-picosecond laser-plasma interaction

Sadaoki Kojima, Masayasu Hata, Natsumi Iwata, Yasunobu Arikawa, Alessio Morace, Shohei Sakata, Seungho Lee, Kazuki Matsuo, King Fai, Farley Law, Hiroki Morita, Yugo Ochiai, Akifumi Yogo, Hideo Nagatomo, Tetsuo Ozaki, Tomoyuki Johzaki, Atsushi Sunahara, Hitoshi Sakagami, Zhe Zhang, Shota Tosaki, Yuki Abe, Junji Kawanaka, Shigeki Tokita, Mitsuo Nakai, Hiroaki Nishimura, Hiroyuki Shiraga, Hiroshi Azechi, Yasuhiko Sentoku, Shinsuke Fujioka

Communications Physics 2 ( 1 ) 2019.12

© 2019, The Author(s). The dependence of the mean kinetic energy of laser-accelerated relativistic electrons (REs) on the laser intensity, so-called ponderomotive scaling, explains well the experimental results to date; however, this scaling is no longer applicable to multi-picosecond (multi-ps) laser experiments. Here, the production of REs was experimentally investigated via multi-ps relativistic laser–plasma-interaction (LPI). The lower slope temperature shows little dependence on the pulse duration and is close to the ponderomotive scaling value, while the higher slope temperature appears to be affected by the pulse duration. The higher slope temperature is far beyond the ponderomotive scaling value, which indicates super-ponderomotive REs (SP-REs). Simulation and experimental evidence are provided to indicate that the SP-REs are produced by LPI in an under-critical plasma, where a large quasi-static electromagnetic field grows rapidly after a threshold timing during multi-ps LPI.

Enhancing laser beam performance by interfering intense laser beamlets Reviewed

A. Morace, N. Iwata, Y. Sentoku, K. Mima, Y. Arikawa, A. Yogo, A. Andreev, S. Tosaki, X. Vaisseau, Y. Abe, S. Kojima, S. Sakata, M. Hata, S. Lee, K. Matsuo, N. Kamitsukasa, T. Norimatsu, J. Kawanaka, S. Tokita, N. Miyanaga, H. Shiraga, Y. Sakawa, M. Nakai, H. Nishimura, H. Azechi, S. Fujioka, R. Kodama

Nature Communicons 10 ( 1 ) 2995 2019.7

Increasing the laser energy absorption into energetic particle beams represents a longstanding quest in intense laser-plasma physics. During the interaction with matter, part of the laser energy is converted into relativistic electron beams, which are the origin of secondary sources of energetic ions, γ-rays and neutrons. Here we experimentally demonstrate that using multiple coherent laser beamlets spatially and temporally overlapped, thus producing an interference pattern in the laser focus, significantly improves the laser energy conversion efficiency into hot electrons, compared to one beam with the same energy and nominal intensity as the four beamlets combined. Two-dimensional particle-in-cell simulations support the experimental results, suggesting that beamlet interference pattern induces a periodical shaping of the critical density, ultimately playing a key-role in enhancing the laser-to-electron energy conversion efficiency. This method is rather insensitive to laser pulse contrast and duration, making this approach robust and suitable to many existing facilities.

A large-aperture high-sensitivity avalanche image intensifier panel

Y. Arikawa, S. Matsubara, H. Kishimoto, Y. Abe, S. Sakata, A. Morace, R. Mizutani, J. Nishibata, A. Yogo, M. Nakai, H. Shiraga, H. Nishimura, S. Fujioka, R. Kodama

Review of Scientific Instruments 89 ( 10 ) 2018.10

© 2018 Author(s). A large-aperture high-sensitivity image intensifier panel that consists of an avalanche photodiode array and a light-emitting diode array is presented. The device has 40% quantum efficiency, over 104 optical gain, and 80-ns time resolution. The aperture size of the device is 20 cm, and with the current manufacturing process, it can be scaled to arbitrarily larger sizes. The device can intensify the light from a single particle scintillation emission to an eye-visible bright flash. The image resolution of the device is currently limited by the size of the avalanche photodiode that is 2 mm, although it can be scaled to smaller sizes in the near future. The image intensifier is operated at a small voltage, typically +57 V. The device can be applied to various applications, such as scintillation imaging, night vision cameras, and an image converter from non-visible light (such as infrared or ultraviolet) to visible light.

A multichannel gated neutron detector with reduced afterpulse for low-yield neutron measurements in intense hard X-ray backgrounds Reviewed

Y. Abe, N. Nakajima, Y. Sakaguchi, Y. Arikawa, S. R. Mirfayzi, S. Fujioka, T. Taguchi, K. Mima, A. Yogo, H. Nishimura, H. Shiraga, M. Nakai

Review of Scientific Instruments 89 ( 10 ) 2018.10

© 2018 Author(s). A design of multichannel gated photomultiplier tube (PMT) is presented for the 960-channel neutron time-of-flight detector at the Institute of Laser Engineering of Osaka University. This is important for the fusion science and the nuclear photonics where intense hard X-rays are generated from the interaction of ultra-short laser pulse of petawatt power density with matter. The hard X-rays often overload PMTs and cause signal-induced background noises called afterpulses, making the detection of subsequent neutrons impossible. For this reason, the PMTs are coupled with an electrical time-gating (ETG) system to avoid overloading. The ETG system disables the PMT by modulating the dynode potential during the primary X-ray flash. An after-pulsing suppression technique is demonstrated by applying a reverse bias voltage between the photocathode and the first dynode. The presented multichannel scheme provides a gate response time of 80 ns, a signal cutoff ratio of 2.5 × 102, and requires reasonably low power consumption.

Magnetized fast isochoric laser heating for efficient creation of ultra-high-energy-density states Reviewed

Shohei Sakata, Seungho Lee, Hiroki Morita, Tomoyuki Johzaki, Hiroshi Sawada, Yuki Iwasa, Kazuki Matsuo, King Fai Farley Law, Akira Yao, Masayasu Hata, Atsushi Sunahara, Sadaoki Kojima, Yuki Abe, Hidetaka Kishimoto, Aneez Syuhada, Takashi Shiroto, Alessio Morace, Akifumi Yogo, Natsumi Iwata, Mitsuo Nakai, Hitoshi Sakagami, Tetsuo Ozaki, Kohei Yamanoi, Takayoshi Norimatsu, Yoshiki Nakata, Shigeki Tokita, Noriaki Miyanaga, Junji Kawanaka, Hiroyuki Shiraga, Kunioki Mima, Hiroaki Nishimura, Mathieu Bailly-Grandvaux, Joao Jorge Santos, Hideo Nagatomo, Hiroshi Azechi, Ryosuke Kodama, Yasunobu Arikawa, Yasuhiko Sentoku, Shinsuke Fujioka

NATURE COMMUNICATIONS 9 2018.9

Fast isochoric heating of a pre-compressed plasma core with a high-intensity short-pulse laser is an attractive and alternative approach to create ultra-high-energy-density states like those found in inertial confinement fusion (ICF) ignition sparks. Laser-produced relativistic electron beam (REB) deposits a part of kinetic energy in the core, and then the heated region becomes the hot spark to trigger the ignition. However, due to the inherent large angular spread of the produced REB, only a small portion of the REB collides with the core. Here, we demonstrate a factor-of-two enhancement of laser-to-core energy coupling with the magnetized fast isochoric heating. The method employs a magnetic field of hundreds of Tesla that is applied to the transport region from the REB generation zone to the core which results in guiding the REB along the magnetic field lines to the core. This scheme may provide more efficient energy coupling compared to the conventional ICF scheme.

Effect of equation of state on laser imprinting by comparing diamond and polystyrene foils Reviewed

H. Kato, K. Shigemori, H. Nagatomo, M. Nakai, T. Sakaiya, T. Ueda, H. Terasaki, Y. Hironaka, K. Shimizu, H. Azechi

Physics of Plasmas 25 ( 3 ) 2018.3

© 2018 Author(s). We present herein a comprehensive study of how the equation of state affects laser imprinting by nonuniform laser irradiation of an inertial fusion target. It has been suggested that a stiffer and denser material would reduce laser imprinting based on the equation of motion with pressure perturbation. We examine the detailed temporal evolution of the imprint amplitude by using the two-dimensional radiation hydrodynamic simulation PINOCO-2D for diamond, which is a candidate stiff-ablator material for inertial fusion targets. The simulated laser imprinting amplitude is compared with experimental measurements of areal-density perturbations obtained by using face-on x-ray backlighting for diamond and polystyrene (PS) (the latter as a reference). The experimental results are well reproduced by the results of the PINOCO-2D simulation, which indicates that the imprinting amplitude due to nonuniform irradiation (average intensity, 4.0 × 1012 to 5.0 × 1013) differs by a factor of two to three between diamond and PS. The difference in laser imprinting is mainly related to the material density and compressibility. These parameters are key factors that determine the laser imprinting amplitude.

Whispering Gallery Effect in Relativistic Optics Reviewed

Y. Abe, K. F.F. Law, Ph Korneev, S. Fujioka, S. Kojima, S. H. Lee, S. Sakata, K. Matsuo, A. Oshima, A. Morace, Y. Arikawa, A. Yogo, M. Nakai, T. Norimatsu, E. d’Humières, J. J. Santos, K. Kondo, A. Sunahara, S. Gus’kov, V. Tikhonchuk

JETP Letters 107 ( 6 ) 351 - 354 2018.3

© 2018, Pleiades Publishing, Inc. A relativistic laser pulse, confined in a cylindrical-like target, under specific conditions may perform multiple scattering along the internal target surface. This results in the confinement of the laser light, leading to a very efficient interaction. The demonstrated propagation of the laser pulse along the curved surface is just yet another example of the “whispering gallery” effect, although nonideal due to laser–plasma coupling. In the relativistic domain its important feature is a gradual intensity decrease, leading to changes in the interaction conditions. The process may pronounce itself in plenty of physical phenomena, including very efficient electron acceleration and generation of relativistic magnetized plasma structures.

Efficient and repetitive neutron generation by double-laser-pulse driven photonuclear reaction

Yasunobu Arikawa, Yusuke Kato, Yuki Abe, Shuto Matsubara, Hidetaka Kishimoto, Nozomi Nakajima, Alessio Morace, Akifumi Yogo, Hiroaki Nishimura, Mitsuo Nakai, Shinsuke Fujioka, Hiroshi Azechi, Kunioki Mima, Shunsuke Inoue, Yoshihide Nakamiya, Kensuke Teramoto, Masaki Hashida, Shuji Sakabe

Plasma and Fusion Research 13 2018.1

© 2018 The Japan Society of Plasma Science and Nuclear Fusion Research. A short and high-intensity neutron pulse can be produced efficiently by using photonuclear reactions caused by Bremsstrahlung hard X-rays in a lase-irradiated high-Z target. The efficient and repetitive neutron generation was demonstrated with the combination of 1 Hz, 0.5 J, 25 fs, 5 x 1019W/cm2laser pulses and a rotating tungsten disc targe. Here we applied double laser pulse irradiation scheme to increase the neutron generation efficiency. The first low-intensity laser pulse produces a lon-scale unde-critical-density plasma on the tungsten target surface prior to the second pulse irradiatio. High energy electrons above the ponderomotive scaling value are accelerated by the second hig-intensity pulse in the preformed plasm, this results in the increment of hard X-ray photons and photonuclear neutron. 3.5 x 104neutron/pulse was obtained with optimized laser irradiation conditions.

3 × 108 D-D neutron generation by high-intensity laser irradiation onto the inner surface of spherical CD shells

Nakahiro Satoh, Takeshi Watari, Katsunobu Nishihara, Koji Matsukado, Ryo Yoshimura, Naoki Akiyama, Masaru Takagi, Toshiyuki Kawashima, Yuki Abe, Yasunobu Arikawa, Atsushi Sunahara, Yoichiro Hironaka, Keisuke Shigemori, Shinsuke Fujioka, Mitsuo Nakai, Hiroshi Azechi

Plasma and Fusion Research 13 2018.1

© 2019 The Japan Society of Plasma Science and Nuclear Fusion Research. 3 × 108 deuterium-deuterium (D-D) neutron generation per pulse was achieved with one-sided laser irradiation through an inlet hole of a deuterated polystyrene shell and a laser intensity of (2-3) × 1016W/cm2. X-ray pinhole camera images displayed a surprisingly uniform hot core formation at the center of the shell. Neutron time-of-flight spectra were recorded at three different angles from the laser incident axis to investigate the directional dependence. The dependence of neutron yield on laser energy, shell diameter, and inlet hole diameter is also discussed. To explain the number of the observed neutrons, a simple model, based on a central expansion of two-electron-temperature (hot and cold) plasma, is presented under assumed hot and cold electron temperature. According to this model, more than 1010 neutrons per pulse, the average amount required for many industrial applications, could be generated by using a higher intensity laser.

Plasma mirror implementation on LFEX laser for ion and fast electron fast ignition Reviewed

A. Morace, S. Kojima, Y. Arikawa, S. Fujioka, A. Yogo, S. Tosaki, S. Sakata, Y. Abe, S. H. Lee, K. Matsuo, A. Sagisaka, K. Kondo, A. S. Pirozhkov, T. Norimatsu, T. Jitsuno, N. Miyanaga, H. Shiraga, M. Nakai, H. Nishimura, H. Azechi

NUCLEAR FUSION 57 ( 12 ) 2017.12

In this work we report the successful implementation of plasma mirror (PM) technology on an LFEX laser facility at the Institute of Laser Engineering, Osaka University. The LFEX laser pulse was successfully refocused at the target chamber center (TCC) by means of a spherical plasma mirror, resulting in 5 x 10(18) W cm(-2) laser intensity, with 45% reflectivity at a laser flux of about 90 J cm(-2) on the PM. Experimental results show stable focusing and pointing of the LFEX pulse after PM refocusing. The contrast improvement was demonstrated by both cooler fast electron slope temperature distribution as well as by the ability to shoot sub-mu m plastic foils obtaining proton beams with maximum energy exceeding 20 MeV. Experimental results are qualitatively reproduced by 2D particle in cell simulations.

Production of intense, pulsed, and point-like neutron source from deuterated plastic cavity by mono-directional kilo-joule laser irradiation Reviewed

Y. Abe, A. Sunahara, S. Lee, T. Yanagawa, Z. Zhang, Y. Arikawa, A. Morace, T. Nagai, T. Ikenouchi, S. Tosaki, S. Kojima, S. Sakata, N. Satoh, T. Watari, K. Nishihara, T. Kawashima, A. Yogo, H. Sakagami, H. Shiraga, H. Nishimura, K. Mima, H. Azechi, T. Norimatsu, M. Nakai, S. Fujioka

APPLIED PHYSICS LETTERS 111 ( 23 ) 2017.12

This paper reports an experimental investigation of a scheme to produce an intense, pulsed, point-like, and quasi-monoenergy neutron source. In this scheme, the inner wall of a deuterated plastic spherical cavity is mono-directionally irradiated by a 2.4 kJ laser beam through an open-tip gold cone inserted into the cavity. The whole inner wall of the cavity is illuminated by laser light owing to multiple laser reflections, and the laser-ablated plasma stagnates near the center of the cavity, at which a several keV hot spot is generated. Thermonuclear and beam D-D fusion reactions occur in the hot spot. We have demonstrated the neutron yield exceeding 10 7 neutrons per pulse from a <100 mu m diameter hot spot with the deuterated plastic cavity and mono-directional GEKKO-XII laser irradiation. Published by AIP Publishing.

Evaluation of laser-driven ion energies for fusion fast-ignition research Reviewed

S. Tosaki, A. Yogo, K. Koga, K. Okamoto, S. Shokita, A. Morace, Y. Arikawa, S. Fujioka, M. Nakai, H. Shiraga, H. Azechi, H. Nishimura

PROGRESS OF THEORETICAL AND EXPERIMENTAL PHYSICS ( 10 ) 2017.10

We investigate laser-driven ion acceleration using kJ-class picosecond (ps) laser pulses as a fundamental study for ion-assisted fusion fast ignition, using a newly developed Thomson-parabola ion spectrometer (TPIS). The TPIS has a space-and weight-saving design, considering its use in an laser-irradiation chamber in which 12 beams of fuel implosion laser are incident, and, at the same time, demonstrates sufficient performance with its detectable range and resolution of the ion energy required for fast-ignition research. As a fundamental study on laser-ion acceleration using a ps pulse laser, we show proton acceleration up to 40 MeV at 1 x 10(19) Wcm(-2). The energy conversion efficiency from the incident laser into protons higher than 6 MeV is 4.6%, which encourages the realization of fusion fast ignition by laser-driven ions.

Second harmonics generation by LFEX laser Invited Reviewed

2017.9

Assessing infrared intensity using the evaporation rate of liquid hydrogen inside a cryogenic integrating sphere for laser fusion targets Reviewed

K. Iwano, A. Iwamoto, T. Asahina, K. Yamanoi, Y. Arikawa, H. Nagatomo, M. Nakai, T. Norimatsu, H. Azechi

REVIEW OF SCIENTIFIC INSTRUMENTS 88 ( 7 ) 2017.7

Infrared (IR) heating processes have been studied to form a deuterium layer in an inertial confinement fusion target. To understand the relationship between the IR intensity and the fuel layering time constant, we have developed a new method to assess the IR intensity during irradiation. In our method, a glass flask acting as a dummy target is filled with liquid hydrogen (LH2) and is then irradiated with 2-mu m light. The IR intensity is subsequently calculated from the time constant of the LH2 evaporation rate. Although LH2 evaporation is also caused by the heat inflow from the surroundings and by the background heat, the evaporation rate due to IR heating can be accurately determined by acquiring the time constant with and without irradiation. The experimentally measured IR intensity is 0.66 mW/cm(2), which agrees well with a value estimated by considering the IR photon energy balance. Our results suggest that the present method can be used to measure the IR intensity inside a cryogenic system during IR irradiation of laser fusion targets. Published by AIP Publishing.

Improvement in the heating efficiency of fast ignition inertial confinement fusion through suppression of the preformed plasma Reviewed

Y. Arikawa, S. Kojima, A. Morace, M. Hata, S. Sakata, S. Fujioka, T. Kawashima, Y. Hironaka, K. Shigemori, Y. Abe, Z. Zhang, X. Vaisseau, S. Lee, T. Gawa, K. Matsuo, K. F. F. Law, Y. Kato, S. Matsubara, S. Tosaki, A. Yogo, H. Nagatomo, S. Tokita, Y. Nakata, T. Jitsuno, N. Miyanaga, J. Kawanaka, Y. Fujimoto, K. Yamanoi, T. Norimatsu, M. Nakai, H. Nishimura, H. Shiraga, H. Azechi, A. Sunahara, T. Johzaki, T. Ozaki, H. Sakagami

NUCLEAR FUSION 57 ( 6 ) 2017.6

The study of fast electron spectrum optimization by suppression of preformed plasma in fast ignition targets is presented in this work. Integrated fast-electron spectra for electron energies below 3 MeV-the energy range responsible for core heating-are compared for different preformed plasma conditions. The pulse contrast (the ratio of peak-to-pedestal laser intensities) is compared for 10(8), 10(9) and 10(11) conditions at constant laser energy (similar to 500 J), pulse duration (2 ps), spot size (30% encircled energy on 50 mu m diameter) and laser intensity (around 1 x 10(19) W cm(-2)). The best electron spectrum optimization, consisting of maximized electron number for energies below 3 MeV was obtained with 14 mu m thick cone targets. The energy coupling efficiency from heating laser to core plasma, assuming typical core plasma parameters, was estimated to be 2%, although 0.37% was obtained with previous conditions with poor pulse contrast and a 7 mu m thick cone target.

High pressure band gap modification of LiCaAlF6 Reviewed

Toshihiko Shimizu, Mui Viet Luong, Marilou Cadatal-Raduban, Melvin John F. Empizo, Kohei Yamanoi, Ren Arita, Yuki Minami, Nobuhiko Sarukura, Nakai Mitsuo, Hiroshi Azechi, Minh Hong Pham, Hung Dai Nguyen, Kouhei Ichiyanagi, Shunsuke Nozawa, Ryo Fukaya, Shin-ichi Adachi, Kazutaka G. Nakamura, Kentaro Fukuda, Yoshiyuki Kawazoe, Krista G. Steenbergen, Peter Schwerdtfeger

APPLIED PHYSICS LETTERS 110 ( 14 ) 2017.4

First-principles density functional calculations together with experimental measurements demonstrate that pressure (uniform and uniaxial) increases the band gap of a perfect lithium hexafluoroaluminate (LiCaAlF6, LiCAF) crystal. As fluoride crystals can be highly transmitting at vacuum ultraviolet wavelengths, crystal modifications that further increase the band gap are highly sought after for future Vacuum ultraviolet applications. Through an extensive series of density functional theory simulations, we demonstrate that the band gap increases monotonically from 12.2 eV to 14.1 eV with the application of uniform pressure. Through joint theoretical and experimental investigation, we explore different uniaxial compressions that can be achieved through cutting-edge laser-shock compression. We find that uniaxial pressure also increases the LiCAF band gap by 0.3 and 0.4 eV for a-and c-axis compressions, respectively. Published by AIP Publishing.

Boosting laser-ion acceleration with multi-picosecond pulses Reviewed

A. Yogo, K. Mima, N. Iwata, S. Tosaki, A. Morace, Y. Arikawa, S. Fujioka, T. Johzaki, Y. Sentoku, H. Nishimura, A. Sagisaka, K. Matsuo, N. Kamitsukasa, S. Kojima, H. Nagatomo, M. Nakai, H. Shiraga, M. Murakami, S. Tokita, J. Kawanaka, N. Miyanaga, K. Yamanoi, T. Norimatsu, H. Sakagami, S. V. Bulanov, K. Kondo, H. Azechi

SCIENTIFIC REPORTS 7 2017.2

Using one of the world most powerful laser facility, we demonstrate for the first time that high-contrast multi-picosecond pulses are advantageous for proton acceleration. By extending the pulse duration from 1.5 to 6 ps with fixed laser intensity of 10(18) W cm(-2), the maximum proton energy is improved more than twice (from 13 to 33 MeV). At the same time, laser-energy conversion efficiency into the MeV protons is enhanced with an order of magnitude, achieving 5% for protons above 6 MeV with the 6 ps pulse duration. The proton energies observed are discussed using a plasma expansion model newly developed that takes the electron temperature evolution beyond the ponderomotive energy in the over picoseconds interaction into account. The present results are quite encouraging for realizing ion-driven fast ignition and novel ion beamlines.

Large-aperture fast-neutron imaging detector with 10-ns time resolution Reviewed

Y. Arikawa, S. Matsubara, Y. Abe, Y. Kato, H. Kishimoto, A. Yogo, H. Nishimura, M. Nakai, H. Shiraga, S. Fujioka, H. Azechi, Y. Otake, K. Mima, Y. Honda

SELECTED PAPERS FROM THE 31ST INTERNATIONAL CONGRESS ON HIGH-SPEED IMAGING AND PHOTONICS 10328 2017

Fast neutrons, which are neutrons with energies greater than 1 MeV, are expected to be a source of nondestructive inspection for a large-size infrastructure such as a bridge girder because of their mean free path exceeding the meter. A neutron-imaging device with 10-ns time resolution can discriminate pulsed neutrons from X-rays via time of flight. For this purpose, we require a fast-response neutron imager with large aperture and high image resolution.
A neutron-imaging device with time resolution of 10 ns and aperture size of 40 cm x 60 cm was developed. It was filled with fast response liquid scintillator [1] in an aluminum honeycomb plate, which converts neutrons to optical light images. The scintillation light images were relayed using an optical lens and detected using a fast response image intensified CCD. The detector was tested at an electron linear accelerator (LINAC) facility in Osaka University. A short X-ray pulse (30 ps pulse duration) was generated using LINAC, and X-ray radiograph images were obtained with a 10-ns exposure time duration. The radiograph images were well attenuated within 10-ns from the X-ray injection. A high-energy X-ray image and a neutron radiograph image of a 30-cm thick concrete block with iron blocks located behind it were successfully observed. This promising technique could facilitate nondestructive inspection of large concrete constructions.

Ablation-erosion analyses of various fusion material surfaces and developments of surface erosion monitors for notification of fusion chamber maintenance times, as an example: Visible light transparent SiC and up-conversion phosphors applied to plasma facing surface structures, useful for versatile purposes to protect and diagnose fusion chambers and so on Reviewed

K. Kasuya, S. Motokoshi, S. Taniguchi, M. Nakai, K. Tokunaga, K. Kolacek, J. Schmidt, O. Frolov, J. Straus, J. Matejicek, A. Choukourov

XXI INTERNATIONAL SYMPOSIUM ON HIGH POWER LASER SYSTEMS AND APPLICATIONS 2016 10254 2017

Two kinds of pulsed lasers in Japan and Czech Republic were used to irradiate various sample materials to investigate the surface erosion thresholds under very hazardous environments including nuclear fusion chambers. The first was ArF laser in ILT and the second was XUV laser in IPP. These data were in-cooperated with our former data to build up our material strength data for our succeeding applications of various materials to a variety of fields. As an example, we proposed surface erosion monitors to notice the fusion chamber maintenance times with which the facilities can be protected from the collapses under very severe operation conditions. These kinds of monitors are expected to be useful for future different kinds of mechanical structures not only for the fusion chambers but also various chambers for many purposes. Special up-conversion phosphors are also newly proposed to be used as the candidate materials to measure the thermal inputs onto the front surfaces of the armor structures. Optical transparent SiC was also newly tested to enrich our data base for our future diagnostic and protection possibilities.

Radio-chromic Film calibration to diagnose laser accelerated protons Reviewed

Kamitsukasa N., Tosaki S., Yogo A., Tojo S., Takahisa K., Aoi N., Fukuda M., Nakai M., Shiraga H., Azechi H., Morace A., Arikawa Y., Abe Y., Kato H., Gawa T., Matsubara S., Nakajima N., Law F.

Meeting Abstracts of the Physical Society of Japan 72 ( 0 ) 924 - 924 2017

Ultrahigh-contrast kilojoule-class petawatt LFEX laser using a plasma mirror Reviewed

Yasunobu Arikawa, Sadaoki Kojima, Alessio Morace, Shohei Sakata, Takayuki Gawa, Yuki Taguchi, Yuki Abe, Zhe Zhang, Xavier Vaisseau, Seung Ho Lee, Kazuki Matsuo, Shota Tosaki, Masayasu Hata, Koji Kawabata, Yuhei Kawakami, Masato Ishida, Koichi Tsuji, Satoshi Matsuo, Noboru Morio, Tetsuji Kawasaki, Shigeki Tokita, Yoshiki Nakata, Takahisa Jitsuno, Noriaki Miyanaga, Junji Kawanaka, Hideo Nagatomo, Akifumi Yogo, Mitsuo Nakai, Hiroaki Nishimura, Hiroyuki Shiraga, Shinsuke Fujioka, Hiroshi Azechi, Atsushi Sunahara, Tomoyuki Johzaki, Tetsuo Ozaki, Hitoshi Sakagami, Akito Sagisaka, Koichi Ogura, Alexander S. Pirozhkov, Masaharu Nishikino, Kiminori Kondo, Shunsuke Inoue, Kensuke Teramoto, Masaki Hashida, Shuji Sakabe

APPLIED OPTICS 55 ( 25 ) 6850 - 6857 2016.9

Laser pulse contrast exceeding 1011 was demonstrated on a kilojoule-class petawatt laser for fast ignition experiments (LFEX) laser system [J. Phys. IV France 133, 81 (2006)] by implementing a 2 in. plasma mirror. Laser beams of up to 1.2 kJ striking the plasma mirror with a pulse duration of 1.5 ps were reflected and focused onto a target without significant distortions in the focal spot. Transmitted light from the plasma mirror reveals that it has a high reflectivity 2 ps before the main peak. The estimated laser pulse contrast at the target was 1011 at 1 ns before the main peak. No preformed plasma was observed with optical interferometry diagnostics, but in the experiment without a plasma mirror a preplasma was clearly observed. The energetic proton was generated from a 0.1 mu m thick CH film showing excellent pulse contrast. This technique constitutes a promising method to enhance the LFEX laser system performance in fast ignition experiments. (C) 2016 Optical Society of America

Fast ignition realization experiment with high-contrast kilo-joule peta-watt LFEX laser and strong external magnetic field Reviewed

Shinsuke Fujioka, Yasunobu Arikawa, Sadaoki Kojima, Tomoyuki Johzaki, Hideo Nagatomo, Hiroshi Sawada, Seung Ho Lee, Takashi Shiroto, Naofumi Ohnishi, Alessio Morace, Xavier Vaisseau, Shohei Sakata, Yuki Abe, Kazuki Matsuo, King Fai Farley Law, Shota Tosaki, Akifumi Yogo, Keisuke Shigemori, Yoichiro Hironaka, Zhe Zhang, Atsushi Sunahara, Tetsuo Ozaki, Hitoshi Sakagami, Kunioki Mima, Yasushi Fujimoto, Kohei Yamanoi, Takayoshi Norimatsu, Shigeki Tokita, Yoshiki Nakata, Junji Kawanaka, Takahisa Jitsuno, Noriaki Miyanaga, Mitsuo Nakai, Hiroaki Nishimura, Hiroyuki Shiraga, Kotaro Kondo, Mathieu Bailly-Grandvaux, Claudio Bellei, Joao Jorge Santos, Hiroshi Azechi

PHYSICS OF PLASMAS 23 ( 5 ) 2016.5

A petawatt laser for fast ignition experiments (LFEX) laser system [N. Miyanaga et al., J. Phys. IV France 133, 81 (2006)], which is currently capable of delivering 2 kJ in a 1.5 ps pulse using 4 laser beams, has been constructed beside the GEKKO-XII laser facility for demonstrating efficient fast heating of a dense plasma up to the ignition temperature under the auspices of the Fast Ignition Realization EXperiment (FIREX) project [H. Azechi et al., Nucl. Fusion 49, 104024 (2009)]. In the FIREX experiment, a cone is attached to a spherical target containing a fuel to prevent a corona plasma from entering the path of the intense heating LFEX laser beams. The LFEX laser beams are focused at the tip of the cone to generate a relativistic electron beam (REB), which heats a dense fuel core generated by compression of a spherical deuterized plastic target induced by the GEKKO-XII laser beams. Recent studies indicate that the current heating efficiency is only 0.4%, and three requirements to achieve higher efficiency of the fast ignition (FI) scheme with the current GEKKO and LFEX systems have been identified: (i) reduction of the high energy tail of the REB; (ii) formation of a fuel core with high areal density using a limited number (twelve) of GEKKOXII laser beams as well as a limited energy (4 kJ of 0.53-mu m light in a 1.3 ns pulse); (iii) guiding and focusing of the REB to the fuel core. Laser-plasma interactions in a long-scale plasma generate electrons that are too energetic to efficiently heat the fuel core. Three actions were taken to meet the first requirement. First, the intensity contrast of the foot pulses to the main pulses of the LFEX was improved to > 10(9). Second, a 5.5-mm-long cone was introduced to reduce pre-heating of the inner cone wall caused by illumination of the unconverted 1.053-mu m light of implosion beam (GEKKO-XII). Third, the outside of the cone wall was coated with a 40-mu m plastic layer to protect it from the pressure caused by imploding plasma. Following the above improvements, conversion of 13% of the LFEX laser energy to a low energy portion of the REB, whose slope temperature is 0.7 MeV, which is close to the ponderomotive scaling value, was achieved. To meet the second requirement, the compression of a solid spherical ball with a diameter of 200-mu m to form a dense core with an areal density of similar to 0.07 g/cm(2) was induced by a laser-driven spherically converging shock wave. Converging shock compression is more hydrodynamically stable compared to shell implosion, while a hot spot cannot be generated with a solid ball target. Solid ball compression is preferable also for compressing an external magnetic field to collimate the REB to the fuel core, due to the relatively small magnetic Reynolds number of the shock compressed region. To meet the third requirement, we have generated a strong kilo-tesla magnetic field using a laser-driven capacitor-coil target. The strength and time history of the magnetic field were characterized with proton deflectometry and a B-dot probe. Guidance of the REB using a 0.6-kT field in a planar geometry has been demonstrated at the LULI 2000 laser facility. In a realistic FI scenario, a magnetic mirror is formed between the REB generation point and the fuel core. The effects of the strong magnetic field on not only REB transport but also plasma compression were studied using numerical simulations. According to the transport calculations, the heating efficiency can be improved from 0.4% to 4% by the GEKKO and LFEX laser system by meeting the three requirements described above. This efficiency is scalable to 10% of the heating efficiency by increasing the areal density of the fuel core. Published by AIP Publishing.

Development of Compton X-ray spectrometer for high energy resolution single-shot high-flux hard X-ray spectroscopy Reviewed

Sadaoki Kojima, Takahito Ikenouchi, Yasunobu Arikawa, Shohei Sakata, Zhe Zhang, Yuki Abe, Mitsuo Nakai, Hiroaki Nishimura, Hiroyuki Shiraga, Tetsuo Ozaki, Shuji Miyamoto, Masashi Yamaguchi, Akinori Takemoto, Shinsuke Fujioka, Hiroshi Azechi

REVIEW OF SCIENTIFIC INSTRUMENTS 87 ( 4 ) 2016.4

Hard X-ray spectroscopy is an essential diagnostics used to understand physical processes that take place in high energy density plasmas produced by intense laser-plasma interactions. A bundle of hard X-ray detectors, of which the responses have different energy thresholds, is used as a conventional single-shot spectrometer for high-flux (>10(13) photons/shot) hard X-rays. However, high energy resolution (Delta hv/hv < 0.1) is not achievable with a differential energy threshold (DET) X-ray spectrometer because its energy resolution is limited by energy differences between the response thresholds. Experimental demonstration of a Compton X-ray spectrometer has already been performed for obtaining higher energy resolution than that of DET spectrometers. In this paper, we describe design details of the Compton X-ray spectrometer, especially dependence of energy resolution and absolute response on photon-electron converter design and its background reduction scheme, and also its application to the laser-plasma interaction experiment. The developed spectrometer was used for spectroscopy of bremsstrahlung X-rays generated by intense laser-plasma interactions using a 200 mu m thickness SiO2 converter. The X-ray spectrum obtained with the Compton X-ray spectrometer is consistent with that obtained with a DET X-ray spectrometer, furthermore higher certainly of a spectral intensity is obtained with the Compton X-ray spectrometer than that with the DET X-ray spectrometer in the photon energy range above 5 MeV. (C) 2016 AIP Publishing LLC.

21aCB-3 Energy absorption ratio evaluation by back scattering of LFEX for Fast Ignitor experiment

Gawa T., Arikawa Y., Kojima S., Morace Alessio, Sakata S., Abe Y., Matsuo K., Tosaki S., Law Farley King Fai, Yogo A., Fujioka S., Nishimura H., Nakai M., Ozaki T., Azechi H.

Meeting Abstracts of the Physical Society of Japan 71 914 - 914 2016

22aCB-6 Laser driven neutron generation experiment by using LFEX

Kato Y., Arikawa Y., Abe Y., Matsubara S., Morace Alessio, Yogo A., Nakai M., Nishimura H., Azechi H.

Meeting Abstracts of the Physical Society of Japan 71 983 - 983 2016

21pAP-5 Energy Distribution and Conversion Efficiency of Fast Electrons Generated with Relativistic Intensity Laser Depending on Pre-plasma Scale II

Kojima Sadaoki, Arikawa Yasunobu, Hata Masayasu, Fujioka Shinsuke, Morace Alessio, Vaisseau Xavier, Pirozhkov Alexander, Zhe Zhang, GEKKO& LFEX Team

Meeting Abstracts of the Physical Society of Japan 71 593 - 593 2016

21aCB-4 Simulation study of inner-irradiation of the shell in the fast ignition scheme

Sunahara A., Abe Y., Ozaki T., Johzaki T., Nagatomo H., Arikawa Y., Fujioka S., Sakagami H., Nakai M., Shiraga H., Norimatsu T., Azechi H.

Meeting Abstracts of the Physical Society of Japan 71 915 - 915 2016

Cool-down performance of the new apparatus for fuel layering demonstrations of FIREX targets Reviewed

A. Iwamoto, T. Norimatsu, M. Nakai, H. Sakagami, H. Shiraga, H. Azechi

8TH INTERNATIONAL CONFERENCE ON INERTIAL FUSION SCIENCES AND APPLICATIONS (IFSA 2013) 688 2016

FIREX targets have been developed under two layering strategies: foam shell and cone guide laser heating methods. Basic studies have been conducted by the collaboration research between ILE and NIFS. Then the next stage requires the characterization of a layered solid fuel. The present system is at the disadvantage of optical observations. Therefore, a new apparatus is designed to solve it. Glass windows with a wide aperture are installed for an interferometer and a microscope. To isolate the vibration from a cryocooler, active vibration control units are equipped, and flexible thermal conductive links are utilized. Furthermore, a quick target exchange mechanism is applied to deal with different types of FIREX targets. A target holder is detachable from a main vacuum chamber. A metal gasket with not fixing bolts but a load of similar to thousand newtons on ensures GHe leak tightness for target cooling. Eventually, the design temperature of 10.00 K at a target container has been achieved. The cool-down performance indecates that the new apparatus provides a cryogenic environment for fuel layering demonstrations.

Energy distribution of fast electrons accelerated by high intensity laser pulse depending on laser pulse duration Reviewed

Sadaoki Kojima, Yasunobu Arikawa, Alessio Morace, Masayasu Hata, Hideo Nagatomo, Tetsuo Ozaki, Shohei Sakata, Seung Ho Lee, Kazuki Matsuo, King Fai Farley Law, Shota Tosaki, Akifumi Yogo, Tomoyuki Johzaki, Atsushi Sunahara, Hitoshi Sakagami, Mitsuo Nakai, Hiroaki Nishimura, Hiroyuki Shiraga, Shinsuke Fujioka, Hiroshi Azechi

9TH INTERNATIONAL CONFERENCE ON INERTIAL FUSION SCIENCES AND APPLICATIONS (IFSA 2015) 717 2016

The dependence of high-energy electron generation on the pulse duration of a high intensity LFEX laser was experimentally investigated. The LFEX laser (A = 1.054 and intensity = 2.5 3 x 10(18) W/cm(2)) pulses were focused on a 1 mm(3) gold cubic block after reducing the intensities of the foot pulse and pedestal by using a plasma mirror. The full width at half maximum (FWHM) duration of the intense laser pulse could be set to either 1.2 ps or 4 ps by temporally stacking four beams of the LFEX laser, for which the slope temperature of the high-energy electron distribution was 0.7 MeV and 1.4 MeV, respectively. The slope temperature increment cannot be explained without considering pulse duration effects on fast electron generation.

Electron transport estimated from electron spectra using electron spectrometer in LFEX laser target experiments Reviewed

T. Ozaki, M. Hata, K. Matsuo, S. Kojima, Y. Arikawa, S. Fujioka, H. Sakagami, A. Sunahara, H. Nagatomo, T. Johzaki, A. Yogo, A. Morace, Z. Zhang, H. Shiraga, S. Sakata, T. Nagai, Y. Abe, S. Lee, M. Nakai, H. Nishimura, H. Azechi

9TH INTERNATIONAL CONFERENCE ON INERTIAL FUSION SCIENCES AND APPLICATIONS (IFSA 2015) 717 2016

Hot electrons which are generated from targets irradiated by a high-intense laser are measured by two electron spectrometers (ESMs). However, total electron energy observed by the ESM is only less than 1 %. Hot electrons are confined by self-fields due to the huge current. When an external magnetic field of several hundred Tesla is applied during the laser irradiation on targets, the ESM signals always increase. In the simulation, the same result can be obtained. The reason is that the Alfven limit can be mitigated due to the external longitudinal magnetic field.

Experimental Test of the Polarization Persistence in Inertial Confinement Fusion Reviewed

J. P. Didelez, C. Deutsch, M. Fujiwara, M. Nakai, M. Utsuro

8TH INTERNATIONAL CONFERENCE ON INERTIAL FUSION SCIENCES AND APPLICATIONS (IFSA 2013) 688 2016

The complete deuteron and triton polarization in the DT fusion increases the reactivity by 50%. For Inertial Confinement Fusion (ICF), due to the dynamics of the fusion reaction process, the fusion rate could even be further increased. It has been argued that the polarization would survive as well in magnetic as in inertial confinements. Recently, we have proposed an experiment to test the persistence of the polarization in a fusion process, using a powerful laser hitting a polarized HD target. The polarized deuterons heated in the plasma induced by the laser can fuse. The corresponding reaction is: D + D -> He-3 + n. The angular distribution of the emitted neutrons and the change in the corresponding total cross section are signatures to estimate the polarization persistency. A proposal to test the persistence of the polarization in ICF has been accepted at ILE: the POLAF project (POlarization in LAser Fusion Process). It uses the polarized HD targets produced at RCNP and the powerful ILE lasers, as well as the neutron detectors existing there. Both institutions are on the same campus at Osaka University. The description of the POLAF experiment and of the corresponding set-up is given.

Mechanical design of experimental apparatus for FIREX cryo-target cooling Reviewed

A. Iwamoto, T. Norimatsu, M. Nakai, H. Sakagami, S. Fujioka, H. Shiraga, H. Azechi

9TH INTERNATIONAL CONFERENCE ON INERTIAL FUSION SCIENCES AND APPLICATIONS (IFSA 2015) 717 2016

Mechanical design of an experimental apparatus for FIREX cryo-target cooling is described. Gaseous helium (GHe) sealing system at a cryogenic environment is an important issue for laser fusion experiments. The dedicated loading system was designed for a metal gasket. We take U-TIGHTSEAL((R)) (Usui Kokusai Sangyo Kaisha. Ltd.) with an indium plated copper jacket as an example. According to its specification, a linear load of 110 N/m along its circumference is the optimum compression; however a lower load would still maintain helium (He) leak below the required level. Its sealing performance was investigated systematically. Our system demanded 27 N/mm of the load to keep He leak tightness in a cryogenic environment. Once leak tightness was obtained, it could be reduced to 9.5 N/mm.

Mitigation of Laser Imprinting with Diamond Ablator for Direct-Drive Inertial Confinement Fusion Targets Reviewed

K. Shigemori, H. Kato, M. Nakai, R. Hosogi, T. Sakaiya, H. Terasaki, S. Fujioka, A. Sunahara, H. Azechi

8TH INTERNATIONAL CONFERENCE ON INERTIAL FUSION SCIENCES AND APPLICATIONS (IFSA 2013) 688 2016

We propose a novel scheme to mitigate the initial perturbation imprinting due to irradiation non-uniformity. Diamond was potential candidate for the ablator material for ICF targets due to its stiffness. The stiffness is very important parameter for imprint mitigation because the laser imprint is primary as a function of pressure perturbation due to lase irradiation non-uniformity. We measured the imprint amplitude of diamond foils and plastic (CH) foils. The experimental data suggest the initial imprinting is drastically mitigated for the diamond foils.

Progress Towards a Laser Produced Relativistic Electron-Positron Pair Plasma Reviewed

Hui Chen, J. Bonlie, R. Cauble, F. Fiuza, W. Goldstein, A. Hazi, C. Keane, A. Link, E. Marley, S. R. Nagel, J. Park, R. Shepherd, G. J. Williams, D. D. Meyerhofer, G. Fiksel, D. Barnak, P. Y. Chang, M. Nakai, Y. Arikawa, H. Azechi, S. Fujioka, S. Kojima, N. Miyanaga, T. Morita, T. Nagai, H. Nishimura, T. Ozaki, Y. Sakawa, H. Takabe, Z. Zhang, S. Kerr, R. Fedosejevs, Y. Sentoku, M. P. Hill, D. J. Hoarty, L. M. R. Hobbs, S. F. James

8TH INTERNATIONAL CONFERENCE ON INERTIAL FUSION SCIENCES AND APPLICATIONS (IFSA 2013) 688 2016

Quantitative K alpha line spectroscopy for energy transport in ultra-intense laser plasma interaction Reviewed

Z. Zhang, H. Nishimura, S. Fujioka, Y. Arikawa, M. Nakai, H. Chen, J. Park, G. J. Williams, T. Ozaki, H. Shiraga, S. Kojima, T. Johzaki, A. Sunahara, N. Miyanaga, J. Kawanaka, Y. Nakata, T. Jitsuno, H. Azechi

8TH INTERNATIONAL CONFERENCE ON INERTIAL FUSION SCIENCES AND APPLICATIONS (IFSA 2013) 688 2016

Absolute Ka line spectroscopy is proposed for studying laser-plasma interactions taking place in the cone-guided fast ignition targets. X-ray spectra ranging from 20 to 100 keV were quantitatively measured with a Laue spectrometer. The absolute sensitivities of the Laue spectrometer system were calibrated using pre-characterized laser-produced x-ray sources and radioisotopes. The integrated reflectivity for the crystal is in good agreement with predictions by an open code for x-ray diffraction. The energy transfer efficiency from incident laser beams to hot electrons, as the energy transfer agency, is derived as a consequence of this work. The absolute yield of Au and Ta Ka lines were measured in the fast ignition experimental campaign performed at Institute of Laser Engineering, Osaka University. Applying the hot electron spectrum information from the electron spectrometer, an energy transfer efficiency of the incident LFEX [1], a kJ-class PW laser, to hot electrons was derived for a planar and cone-guided geometry.

The diagnostics of the energy coupling efficiency in the Fast Ignition integrated experiment Reviewed

Y. Arikawa, S. Fujioka, A. Morace, Z. Zhang, T. Nagai, M. Taga, Y. Abe, S. Kojima, S. Sakata, H. Inoue, M. Utsugi, S. Hattori, S. H. Lee, T. Ikenouchi, T. Hosoda, A. Sunahara, T. Ozaki, T. Johzaki, H. Nagatomo, K. Yamanoi, T. Shimizu, S. Tokita, Y. Fujimoto, J. Kawanaka, Y. Nakata, M. Nakai, H. Shiraga, H. Jitsuno, N. Sarukura, N. Miyanaga, T. Norimatsu, H. Nishimura, H. Azechi

8TH INTERNATIONAL CONFERENCE ON INERTIAL FUSION SCIENCES AND APPLICATIONS (IFSA 2013) 688 2016

The energy coupling efficiency (CE) in Fast Ignition (FI) laser fusion was studied at GEKKO XII and LFEX laser facility by using newly developed targets and plasma diagnostic instruments. The gated-liquid scintillator neutron detectors had been upgraded by using neutron collimators for intense background fluxes of gamma-rays and neutrons in the FI experiment. Clear fusion neutron signal was successfully recorded in the sub-kJ heating FI experiment. Up to 5 times neutron yield enhancement was observed, and the CE of the heating laser to core plasma was estimated to be 1.6 % for cone-in-shell target implosion by 9 beams and core heating by LFEX pulse 115 ps before bang time. The laser-to-electron energy conversion efficiency was separately diagnosed using a newly developed target and resulted to be 45 %. The fast electron energy spectrum was estimated to be 2.3 MeV slope temperature by hard x-ray spectroscopy. Monte Carlo simulations demonstrate the consistency of the data set.

Time evolution of the diamond surface shape due to non-uniform laser irradiation

Kato H., Shigemori K., Ueda T., Nagatomo H., Sakaiya T., Terasaki H., Hironaka Y., Nakai M., Azechi H.

Meeting Abstracts of the Physical Society of Japan 71 583 - 583 2016

Heating efficiency evaluation with mimicking plasma conditions of integrated fast-ignition experiment Reviewed

Shinsuke Fujioka, Tomoyuki Johzaki, Yasunobu Arikawa, Zhe Zhang, Alessio Morace, Takahito Ikenouchi, Tetsuo Ozaki, Takahiro Nagai, Yuki Abe, Sadaoki Kojima, Shohei Sakata, Hiroaki Inoue, Masaru Utsugi, Shoji Hattori, Tatsuya Hosoda, Seung Ho Lee, Keisuke Shigemori, Youichiro Hironaka, Atsushi Sunahara, Hitoshi Sakagami, Kunioki Mima, Yasushi Fujimoto, Kohei Yamanoi, Takayoshi Norimatsu, Shigeki Tokita, Yoshiki Nakata, Junji Kawanaka, Takahisa Jitsuno, Noriaki Miyanaga, Mitsuo Nakai, Hiroaki Nishimura, Hiroyuki Shiraga, Hideo Nagatomo, Hiroshi Azechi

PHYSICAL REVIEW E 91 ( 6 ) 2015.6

A series of experiments were carried out to evaluate the energy-coupling efficiency from heating laser to a fuel core in the fast-ignition scheme of laser-driven inertial confinement fusion. Although the efficiency is determined by a wide variety of complex physics, from intense laser plasma interactions to the properties of high-energy density plasmas and the transport of relativistic electron beams (REB), here we simplify the physics by breaking down the efficiency into three measurable parameters: (i) energy conversion ratio from laser to REB, (ii) probability of collision between the REB and the fusion fuel core, and (iii) fraction of energy deposited in the fuel core from the REB. These three parameters were measured with the newly developed experimental platform designed for mimicking the plasma conditions of a realistic integrated fast-ignition experiment. The experimental results indicate that the high-energy tail of REB must be suppressed to heat the fuel core efficiently.

Quantitative K alpha line spectroscopy for energytransport in fast ignition plasma driven with LFEX PW laser Reviewed

Z. Zhang, H. Nishimura, S. Fujioka, Y. Arikawa, T. Ikenouchi, M. Nakai, H. Nagatomo, H. Chen, J. Park, G. J. Williams, T. Ozaki, H. Shiraga, S. Kojima, H. Hosoda, N. Miyanaga, J. Kawanaka, Y. Nakata, T. Jitsuno, H. Azechi

HIGH ENERGY DENSITY PHYSICS 15 78 - 81 2015.6

Quantitative high-energy X-ray spectroscopy is applied for the laser plasma interaction in the fast ignition scheme. A double tracer layer target is designed for the absolute measurement of hot electron temperature and laser energy transfer efficiency. The hot electron temperature is determined from the ratio of the number of K alpha photons from the first and second tracers. Consequently, the energy transfer efficiency from incident laser beams to hot electrons, as the energy transfer mechanism, is derived. In a cone-guide geometry, we simultaneously measured the hot electron temperature and the energy transfer efficiency from the incident LFEX, a kJ-class PW laser, which were measured to be 5.3 MeV and 37%, respectively. (C) 2015 Elsevier B.V. All rights reserved.

Response measurement of single-crystal chemical vapor deposition diamond radiation detector for intense X-rays aiming at neutron bang-time and neutron burn-history measurement on an inertial confinement fusion with fast ignition Reviewed

T. Shimaoka, J. H. Kaneko, Y. Arikawa, M. Isobe, Y. Sato, M. Tsubota, T. Nagai, S. Kojima, Y. Abe, S. Sakata, S. Fujioka, M. Nakai, H. Shiraga, H. Azechi, A. Chayahara, H. Umezawa, S. Shikata

REVIEW OF SCIENTIFIC INSTRUMENTS 86 ( 5 ) 2015.5

A neutron bang time and burn history monitor in inertial confinement fusion with fast ignition are necessary for plasma diagnostics. In the FIREX project, however, no detector attained those capabilities because high-intensity X-rays accompanied fast electrons used for plasma heating. To solve this problem, single-crystal CVD diamond was grown and fabricated into a radiation detector. The detector, which had excellent charge transportation property, was tested to obtain a response function for intense X-rays. The applicability for neutron bang time and burn history monitor was verified experimentally. Charge collection efficiency of 99.5% +/- 0.8% and 97.1% +/- 1.4% for holes and electrons were obtained using 5.486 MeV alpha particles. The drift velocity at electric field which saturates charge collection efficiency was 1.1 +/- 0.4 x 10(7) cm/s and 1.0 +/- 0.3 x 10(7) cm/s for holes and electrons. Fast response of several ns pulse width for intense X-ray was obtained at the GEKKO XII experiment, which is sufficiently fast for ToF measurements to obtain a neutron signal separately from X-rays. Based on these results, we confirmed that the single-crystal CVD diamond detector obtained neutron signal with good S/N under ion temperature 0.5-1 keV and neutron yield of more than 109 neutrons/shot. (C) 2015 AIP Publishing LLC.

18pCP-10 Effects of material response due to compressibility on laser imprinting

Kato H., Shigemori K., Nakai M., Sakaiya T., Hosogi R., Terasaki H., Nagatomo H., Hironaka Y., Azechi H.

Meeting Abstracts of the Physical Society of Japan 70 679 - 679 2015

24aBH-3 Theory and ignition taget design of fast ignition with irradiation on the inner surface of the

Sunahara A., Johzaki T., Yanagawa T., Sakagami H., Abe Y., Nagai T., Lee S., Zhe Zhang, Ikenouchi T., Kojima S., Sakata S., Arikawa Y., Fujioka S., Nakai M., Shiraga H., Norimatsu T., Azechi H., FIREX project team

Meeting Abstracts of the Physical Society of Japan 70 925 - 925 2015

22aCM-6 Study of Proton Stopping Power in Dense Plasmas

Morace A., Feugeas J-L., Nicolai P., Fujioka S., Arikawa Y., Norimatsu T., Hosokawa H., Honrubia J., Batani D., Jakubowska K., Yogo A., Nakai M., Kojima S., Zhang Z., Abe Y., Mima K., Shiraga H., Nishimura H., Azechi H.

Meeting Abstracts of the Physical Society of Japan 70 861 - 861 2015

19aCP-5 The influence on the fast electron generation from implosion plasma Reviewed

Arikawa Y., Gawa T., Yamamoto T., Matsuo K., Tosaki S., L.K. Fai, Kawashima T., Ueda T., Hironaka Y., Sigemori K., Yogo A., Kojima S., Miyanaga N., Jitsuno T., Kawanaka J., Nakata Y., Tokita S., Nagatomo H., Nihsimura H., Shiraga H., Nakai M., Sunahara A., Fujioka S., Johzaki T., Ozaki T., Sakagami H., Z. Zhang, Azechi H., FIREX group, LFEX group, Alessio M., Hata M., Sakata S., Abe Y., Lee S. H., Kato H.

Meeting Abstracts of the Physical Society of Japan 70 ( 0 ) 698 - 698 2015

19aCP-2 Experimental Study of Transport of Relativistic Electron Beams in Strong Magnetic Mirror Field Reviewed

Sakata S., Arikawa Y., M. Bailly-Grandvaux, C. Bellei, Ozaki T., Hata M., Johzaki T., Sunahara A., Yogo Y., Nakai M., Nishimura H., Kondo K., Shiraga H., Nagatomo H., J. J. Santos, Fujioka S., Azechi H., Hironaka Y., Kojima S., Matsuo K., K. F. Law, S. H. Lee, A. Morace, X. Vaisseau

Meeting Abstracts of the Physical Society of Japan 70 ( 0 ) 695 - 695 2015

24pBH-6 Electron generation experiment for fast ignition using plasma mirror

Arikawa Y., Kojima S., Fujioka S., Morace Alessio, Gawa T., Sakata S., Yogo A., Zhe Zhang, Tokita S., Ikenouchi T., Nagai T., Abe Y., Utsugi M., Lee S. H., Inoue H., Taguchi Y., Matsuo K., Tosaki S., Hata M., Nagatomo H., Sunahara A., Johzaki T., Ozaki T., Sakagami H., Inoue S., Teramoto K., Nakashima Y., Hashida M., Sakabe S., Sagisaka A., Ogura K., Pirozhkov Alexander, Nishikino M., Kondo K., Nishimura H., Shiraga H., Nakai M., FIREX group, LFEX group, Azechi H.

Meeting Abstracts of the Physical Society of Japan 70 953 - 953 2015

High-intensity neutron generation via laser-driven photonuclear reaction Invited

Yasunobu Arikawa, Masaru Utsugi, Morace Alessio, Takahiro Nagai, Yuki Abe, Sadaoki Kojima, Shohei Sakata, Hiroaki Inoue, Shinsuke Fujioka, Zhe Zhang, Hui Chen, Jaebum Park, Jackson Williams, Taichi Morita, Yoichi Sakawa, Yoshiki Nakata, Junji Kawanaka, Takahisa Jitsuno, Nobuhiko Sarukura, Noriaki Miyanaga, Mitsuo Nakai, Hiroyuki Shiraga, Hiroaki Nishimura, Hiroshi Azechi

Plasma and Fusion Research 10 ( SpecialIssue.1 ) 2015 2015

© 2015 The Japan Society of Plasma Science and Nuclear Fusion Research. The generation of high-peak-intensity neutrons through a photonuclear reaction was demonstrated using the Laser for Fast Ignition Experiments (LFEX) at Osaka University. Up to 109 neutrons/shot were generated from a 1mm sized gold target. Using Monte Carlo simulations, the neutron spectrum from keV to MeV was found to be independent of the γ-ray spectrum. The typical peak neutron intensity of 1021 neutrons /cm2/s at the target surface was estimated, and it should be a useful tool for nuclear synthesis experiments.

Laser erosion diagnostics of plasma facing materials with displacement sensors and their application to safeguard monitors to protect nuclear fusion chambers Reviewed

Koichi Kasuya, Shinji Motokoshi, Seiji Taniguchi, Mitsuo Nakai, Kazutoshi Tokunaga, Waldemar Mroz, Bogus Law Budner, Barbara Korczyc

XX INTERNATIONAL SYMPOSIUM ON HIGH-POWER LASER SYSTEMS AND APPLICATIONS 2014 9255 2015

Tungsten and SiC are candidates for the structural materials of the nuclear fusion reactor walls, while CVD poly-crystal diamond is candidate for the window material under the hazardous fusion stresses. We measured the surface endurance strength of such materials with commercial displacement sensors and our recent evaluation method. The pulsed high thermal input was put into the material surfaces by UV lasers, and the surface erosions were diagnosed. With the increase of the total number of the laser shots per position, the crater depth increased gradually. The 3D and 2D pictures of the craters were gathered and compared under various experimental conditions. For example, the maximum crater depths were plotted as a function of shot accumulated numbers, from which we evaluated the threshold thermal input for the surface erosions to be induced. The simple comparison-result showed that tungsten was stronger roughly two times than SiC. Then we proposed how to monitor the surface conditions of combined samples with such diamonds coated with thin tungsten layers, when we use such samples as parts of divertor inner walls, fusion chamber first walls, and various diagnostic windows. We investigated how we might be able to measure the inner surface erosions with the same kinds of displacement sensors. We found out the measurable maximum thickness of such diamond which is useful to monitor the erosion. Additionally we showed a new scheme of fusion reactor systems with injectors for anisotropic pellets and heating lasers under the probable use of W and/or SiC.

Characterizing a fast-response, low-afterglow liquid scintillator for neutron time-of-flight diagnostics in fast ignition experiments Reviewed

Y. Abe, H. Hosoda, Y. Arikawa, T. Nagai, S. Kojima, S. Sakata, H. Inoue, Y. Iwasa, K. Iwano, K. Yamanoi, S. Fujioka, M. Nakai, N. Sarukura, H. Shiraga, T. Norimatsu, H. Azechi

REVIEW OF SCIENTIFIC INSTRUMENTS 85 ( 11 ) 1.10E+127 2014.11

The characteristics of oxygen-enriched liquid scintillators with very low afterglow are investigated and optimized for application to a single-hit neutron spectrometer for fast ignition experiments. It is found that 1,2,4-trimethylbenzene has better characteristics as a liquid scintillator solvent than the conventional solvent, p-xylene. In addition, a benzophenon-doped BBQ liquid scintillator is shown to demonstrate very rapid time response, and therefore has potential for further use in neutron diagnostics with fast time resolution. (C) 2014 AIP Publishing LLC.

Development of multichannel low-energy neutron spectrometer Reviewed

Y. Arikawa, T. Nagai, Y. Abe, S. Kojima, S. Sakata, H. Inoue, M. Utsugi, Y. Iwasa, T. Murata, N. Sarukura, M. Nakai, H. Shiraga, S. Fujioka, H. Azechi

REVIEW OF SCIENTIFIC INSTRUMENTS 85 ( 11 ) 2014.11

A multichannel low-energy neutron spectrometer for down-scattered neutron (DSN) measurements in inertial confinement fusion (ICF) experiments has been developed. Our compact-size 256-channel lithium-glass-scintillator-based spectrometer has been implemented and tested in ICF experiments with the GEKKO XII laser. We have performed time calibration of the 256-channel analog-to-digital convertor system used for DSN measurements via X-ray pulse signals. We have clearly observed the DD-primary fusion neutron signal and have successfully studied the detector's impulse response. Our detector is soon to be implemented in future ICF experiments. (C) 2014 AIP Publishing LLC.

Accuracy evaluation of a Compton X-ray spectrometer with bremsstrahlung X-rays generated by a 6 MeV electron bunch Reviewed

Sadaoki Kojima, Yasunobu Arikawa, Yasuhiko Nishimura, Hiromi Togawa, Zhe Zhang, Takahito Ikenouchi, Tetsuo Ozaki, Alessio Morace, Takahiro Nagai, Yuki Abe, Shouhei Sakata, Hiroaki Inoue, Masaru Utsugi, Mitsuo Nakai, Hiroaki Nishimura, Hiroyuki Shiraga, Ryukou Kato, Shinsuke Fujioka, Hiroshi Azechi

REVIEW OF SCIENTIFIC INSTRUMENTS 85 ( 11 ) 2014.11

A Compton-scattering-based X-ray spectrometer is developed to obtain the energy distribution of fast electrons produced by intense laser and matter interactions. Bremsstrahlung X-rays generated by fast electrons in a material are used to measure fast electrons' energy distribution in matter. In the Compton X-ray spectrometer, X-rays are converted into recoil electrons by Compton scattering in a converter made from fused silica glass, and a magnet-based electron energy analyzer is used to measure the energy distribution of the electrons that recoil in the direction of the incident X-rays. The spectrum of the incident X-rays is reconstructed from the energy distribution of the recoil electrons. The accuracy of this spectrometer is evaluated using a quasi-monoenergetic 6 MeV electron bunch that emanates from a linear accelerator. An electron bunch is injected into a 1.5 mm thick tungsten plate to produce bremsstrahlung X-rays. The spectrum of these bremsstrahlung X-rays is obtained in the range from 1 to 9MeV. The energy of the electrons in the bunch is estimated using a Monte Carlo simulation of particle-matter interactions. The result shows that the spectrometer's energy accuracy is +/- 0.5 MeV for 6.0 MeV electrons. (C) 2014 AIP Publishing LLC.

Photonuclear reaction based high-energy x-ray spectrometer to cover from 2 MeV to 20 MeV Reviewed

S. Sakata, Y. Arikawa, S. Kojima, T. Ikenouchi, T. Nagai, Y. Abe, H. Inoue, A. Morace, M. Utsugi, R. Kato, H. Nishimura, M. Nakai, H. Shiraga, S. Fujioka, H. Azechi

REVIEW OF SCIENTIFIC INSTRUMENTS 85 ( 11 ) 2014.11

A photonuclear-reaction-based hard x-ray spectrometer is developed to measure the number and energy spectrum of fast electrons generated by interactions between plasma and intense laser light. In this spectrometer, x-rays are converted to neutrons through photonuclear reactions, and the neutrons are counted with a bubble detector that is insensitive to x-rays. The spectrometer consists of a bundle of hard x-ray detectors that respond to different photon-energy ranges. Proof-of-principle experiment was performed on a linear accelerator facility. A quasi-monoenergetic electron bunch (N-e = 1.0 x 10(-6) C, E-e = 16 +/- 0.32 MeV) was injected into a 5-mm-thick lead plate. Bremsstrahlung x-rays, which emanate from the lead plate, were measured with the spectrometer. The measured spectral shape and intensity agree fairly well with those computed with a Monte Carlo simulation code. The result shows that high-energy x-rays can be measured absolutely with a photon-counting accuracy of 50%-70% in the energy range from 2 MeV to 20 MeV with a spectral resolution (Delta h nu/h nu) of about 15%. Quantum efficiency of this spectrometer was designed to be 10(-7), 10(-4), 10(-5), respectively, for 2-10, 11-15, and 15-25 MeV of photon energy ranges. (C) 2014 AIP Publishing LLC.

Development of x-ray radiography for high energy density physics Reviewed

A. Morace, L. Fedeli, D. Batani, S. Baton, F. N. Beg, S. Hulin, L. C. Jarrott, A. Margarit, M. Nakai, M. Nakatsutsumi, P. Nicolai, N. Piovella, M. S. Wei, X. Vaisseau, L. Volpe, J. J. Santos

PHYSICS OF PLASMAS 21 ( 10 ) 2014.10

We describe an experiment performed at the LULI laser facility using an advanced radiographic technique that allowed obtaining 2D, spatially resolved images of a shocked buried-code-target. The technique is suitable for applications on Fast Ignition as well as Warm Dense Matter research. In our experiment, it allowed to show cone survival up to Mbar pressures and to measure the shock front velocity and the fluid velocity associated to the laser-generated shock. This allowed obtaining one point on the shock polar of porous carbon. (C) 2014 AIP Publishing LLC.

High intensity g-ray and neutron generation by ultra intense laser Reviewed

Yasunobu Arikawa, Masaru Utsugi, Alessio Morace, Takahiro Nagai, Sadaoki Kojima, Shohei Sakata, Hiroaki Inoue, Shigeki Tokita, Yoshiki Nakata, Junji Kawanaka, Takahisa Jitsuno, Nobuhiko Sarukura, Noriaki Miyanaga, Mitsuo Nakai, Hiroyuki Shiraga, Hiroaki Nishimura, Hiroshi Azechi

ABSTRACTS OF PAPERS OF THE AMERICAN CHEMICAL SOCIETY 248 2014.8

Stabilization of radiation reaction with vacuum polarization Reviewed

Keita Seto, Sen Zhang, James Koga, Hideo Nagatomo, Mitsuo Nakai, Kunioki Mima

PROGRESS OF THEORETICAL AND EXPERIMENTAL PHYSICS ( 4 ) 2014.4

From the development of the electron theory by H. A. Lorentz in 1906, many authors have tried to reformulate this model. P. A. M. Dirac derived the relativistic-classical electron model in 1938, which is now called the Lorentz-Abraham-Dirac model. But this model has the big difficulty of the runaway solution. Recently, this equation has become important for ultra-intense laser-electron (plasma) interactions. For simulations in this research field, it is desirable to stabilize this model of the radiation reaction. In this paper, we will discuss this ability for radiation reaction with the inclusion of vacuum polarization.

Development of compton X-ray spectrometer for fast ignition experiment Reviewed

Sadaoki Kojima, Yasunobu Arikawa, Takahito Ikenouchi, Takahiro Nagai, Yuki Abe, Shouhei Sakata, Hiroaki Inoue, Takuya Namimoto, Shinsuke Fujioka, Mitsuo Nakai, Hiroyuki Shiraga, Tetsuo Ozaki, Makoto R. Asakawa, Ryukou Kato, Hiroshi Azechi

Plasma and Fusion Research 9 ( 3 ) 2014

In the context of Fast Ignition, the fast electron temperature is a key parameter to determine the laserto- fast electron energy conversion efficiency. Bremsstrahlung X-ray (γ-ray) emission represents an attractive alternative to measure this fundamental parameter. In this study, a single-shot high-energy γ-ray spectrometer with sensitivity ranging from 0.5MeV to 7MeV was developed, allowing to estimate the γ-ray spectrum in the fast ignition. © 2014 The Japan Society of Plasma Science and Nuclear Fusion Research.

Energy transportation by mev hot electrons in fast ignition plasma driven with LFEX PW laser Reviewed

Zhe Zhang, Hiroaki Nishimura, Shinsuke Fujioka, Yasunobu Arikawa, Mitsuo Nakai, Hideo Nagatomo, Hiroyuki Shiraga, Sadaoki Kojima, Alessio Morace, Noriaki Miyanaga, Junji Kawanaka, Yoshiki Nakata, Takahisa Jitsuno, Hiroshi Azechi, Tetsuo Ozaki, Hui Chen, Jaebum Park, Gerald Jackson Williams, Tomoyuki Johzaki, Atsushi Sunahara

Plasma and Fusion Research 9 2014

Implosion and heating experiments with the scheme of fast ignition (FI) have been performed on Gekko-XII and LFEX laser platform at the Institute of Laser Engineering in Osaka University. A cone-guided CD-shell has been used as a base-line target for the fast ignition realization. The information about energy transfer from LFEX petawatt (PW) laser is quantitatively studied with an absolute Kα diagnostics and a fast electron trajectory simulation. The transfer efficiency (ηTE) is estimated for a planar interaction as a reference and for several types of guiding-cone. As a general trend, the guiding-cone enhanced the ηTE by a factor of 3 comparing with the planar case.

The development of the neutron detector for the fast ignition experiment by using LFEX and gekko XII facility Reviewed

Nagai T, Nakai M, Arikawa Y, Abe Y, Kojima S, Sakata S, Inoue H, Fujioka S, Shiraga H, Sarukura N, Norimatsu T, Azechi H

Plasma and Fusion Research 9 ( SPECIALISSUE.3 ) 2014

The neutron imaging diagnostics and reconstructing technique for fast ignition Reviewed

Inoue H, Arikawa Y, Nozaki S, Fujioka S, Nagai T, Kojima S, Abe Y, Sakata S, Kinjo A, Nakai M, Shiraga H, Azechi H

Plasma and Fusion Research 9 ( SPECIALISSUE.3 ) 2014

Present status of fast ignition realization experiment and inertial fusion energy development Reviewed

H. Azechi, K. Mima, S. Shiraga, S. Fujioka, H. Nagatomo, T. Johzaki, T. Jitsuno, M. Key, R. Kodama, M. Koga, K. Kondo, J. Kawanaka, N. Miyanaga, M. Murakami, K. Nagai, M. Nakai, H. Nakamura, T. Nakamura, T. Nakazato, Y. Nakao, K. Nishihara, H. Nishimura, T. Norimatsu, P. Norreys, T. Ozaki, J. Pasley, H. Sakagami, Y. Sakawa, N. Sarukura, K. Shigemori, T. Shimizu, A. Sunahara, T. Taguchi, K. Tanaka, K. Tsubakimoto, Y. Fujimoto, H. Homma, A. Iwamoto

NUCLEAR FUSION 53 ( 10 ) 2013.10

One of the most advanced fast ignition programmes is the fast ignition realization experiment (FIREX). The goal of its first phase is to demonstrate ignition temperature of 5 keV, followed by the second phase to demonstrate ignition-and-burn. The second series experiment of FIREX-I, from late 2010 to early 2011, has demonstrated a high (>10%) coupling efficiency from laser to thermal energy of the compressed core, suggesting that the ignition temperature can be achieved at laser energy below 10 kJ. Further improvement of the coupling efficiency is expected by introducing laser-driven magnetic fields.

Luminescence properties of Nd3+ and Er3+ doped glasses in the VUV region Reviewed

Kohei Yamanoi, Takahiro Murata, Yasunobu Arikawa, Tomoharu Nakazato, Marilou Cadatal-Raduban, Toshihiko Shimizu, Nobuhiko Sarukura, Mitsuo Nakai, Takayoshi Norimatsu, Hiroaki Nishimura, Hiroshi Azechi, Shigeru Fujino, Hideki Yoshida, Akira Yoshikawa, Nakahiro Satoh, Hirofumi Kan

OPTICAL MATERIALS 35 ( 11 ) 1962 - 1964 2013.9

We report the vacuum ultraviolet (VUV) spectroscopy of APLF + Nd and APLF + Er glass, with composition 20Al(PO3)(3)-80LiF + 1NdF(3) and + 1ErF(3) (in mol%). APLF + Nd and APLF + Er have a dominant fluorescence peak at 185 nm and 168 nm with decay times of 4.5 ns and 5.8 ns, respectively. Fluorescence from APLF + Nd is attributed to 4f(2)5d -> 4f(3) transitions in neodymium (Nd) while fluorescence from APLF + Er is due to spin allowed transition in erbium (Er). This is the first report of VUV fluorescence from rare earth ions doped in glass hosts, which could provide the basis for mass production of VUV emitting materials. Our results also suggest the potential of using APLF + Nd and APLF + Er as neutron scintillators during inertial confinement fusion. (C) 2012 Elsevier B.V. All rights reserved.

Quantitative measurement of hard X-ray spectra from laser-driven fast ignition plasma Reviewed

Z. Zhang, H. Nishimura, T. Namimoto, S. Fujioka, Y. Arikawa, H. Nagatomo, M. Nakai, T. Ozaki, M. Koga, T. Johzaki, A. Sunahara, H. Chen, J. Park, G. J. Williams, H. Shiraga, S. Kojima, M. Nishikino, T. Kawachi, H. Hosoda, Y. Okano, N. Miyanaga, J. Kawanaka, Y. Nakata, T. Jitsuno, H. Azechi

High Energy Density Physics 9 ( 3 ) 435 - 438 2013.9

Absolute K. α line spectroscopy is proposed for studying laser-plasma interactions taking place in the Au cone-guided fast ignition targets. X-ray spectra ranging from 20 to 100keV were quantitatively measured with a Laue spectrometer composed of a cylindrically curved crystal and a filter-absorption method for Bremsstrahlung continuum emission. The absolute sensitivities of the Laue spectrometer systems were calibrated using pre-characterized laser-produced X-ray sources and radioisotopes. The integrated reflectivity for the crystal is in good agreement with predictions by an X-ray diffraction code. The energy transfer efficiency from incident laser beams to hot electrons, as the energy transfer mechanism, is derived from this work. The absolute yield of Au and Ta K. α lines were measured in the fast ignition experimental campaign performed at Institute of Laser Engineering, Osaka University. Applying the hot electron spectrum information from electron spectrometer and scaling laws, the energy transfer efficiency from the incident LFEX, a kJ-class PW laser, to hot electrons was derived for the first time. © 2013 Elsevier B.V.

FIREX foam cryogenic target development: Residual void reduction and estimation with solid hydrogen refractive index measurements Reviewed

A. Iwamoto, T. Fujimura, M. Nakai, T. Norimatsu, H. Sakagami, H. Shiraga, H. Azechi

Nuclear Fusion 53 ( 8 ) 2013.8

Voidless fuel solidification within a foam material is attempted for the development of a Fast Ignition Realization EXperiment (FIREX) target. A typical target consists of a foam shell with a thin solid fuel layer, a gold cone guide and a glass fill tube. The foam layer is formed with aggregations of tiny cells. The porous foam material has the advantage of forming a uniform layer in a liquid state by the effect of capillarity. Random liquid-solid transitions of fuel, however, would cause void spaces in each cell because of their different densities. To form a voidless solid fuel layer in the FIREX target, we propose a layering method, which includes the process of controlled solidification and simultaneous liquid fuel supply to the liquid/solid interface. Normal H 2 is used as a surrogate fuel for our experiments. By applying a resorcinol/formalin aerogel, which has been developed in the Institute of Laser Engineering, Osaka University, instead of a foam material, formation of a solid H2 layer with reduced void spaces is preliminarily demonstrated. Related solid H2 refractive indices are measured to estimate the void fraction. Eventually, its filling factor reaches ∼99%. Furthermore, the application of the proved method is numerically simulated on the FIREX target. The method is confirmed to be applicable in it with a cone guide heating technique. © 2013 IAEA, Vienna.

Report on OPIC Conference on Laser and Accelerator Neutron Sources and Applications '13 (LANSA '13)

NISHIMURA Hiroaki, ARIKAWA Yasunobu, NAKAI Mitsuo

41 ( 7 ) 540 - 542 2013.7

Electronic States of Trivalent Praseodymium Ion Doped in 20Al(PO3)(3)-80LiF Glass Reviewed

Tsuboi Mizuki, Takeda Kohei, Nakazato Tomoharu, Kono Masahiro, Yamanoi Kohei, Cadatal-Raduban Marilou, Sakai Kohei, Nishi Ryosuke, Minami Yuki, Mui Viet Luong, Arikawa Yasunobu, Shimizu Toshihiko, Sarukurua Nobuhiko, Norimatsu Takayoshi, Nakai Mitsuo, Azechi Hiroshi, Murata Takahiro, Fujino Shigeru, Yoshida Hideki, Yoshikawa Akira, Sato Nakahiro, Kan Hirofumi, Kamata Kei

JAPANESE JOURNAL OF APPLIED PHYSICS 52 ( 6 ) 2013.6

We investigate the photoluminescence (PL) and photoluminescence excitation (PLE) spectra of 20Al(PO3)(3)-80LiF+Pr glass (APLF+Pr) and Pr3+-doped LiCaAlF6 crystal (Pr:LiCAF) in order to determine the electronic states of Pr3+ in APLF glass host and to improve APLF+Pr scintillation properties. Ultraviolet (UV) emission bands at around 250 and 340nm were observed from both materials and these can be ascribed to 4f5d -> 4f(2) transitions in Pr3+. Emission at around 400nm was also obtained and is principally attributed to S-1(0) -> 4f(2) transition. Difference in the emission profiles of these two materials was found to be due to the extent of the 5d band and its position relative to the S-1(0) state. Increasing the concentration of Pr3+ up to 2 mol% was found to improve UV emission ratio due to the faster cross-relaxation of 4f states. This could improve the quantum efficiency of APLF+Pr as a neutron scintillator for scattered-neutron diagnostics in laser fusion research. (C) 2013 The Japan Society of Applied Physics

New insights into the laser produced electron-positron pairs Reviewed

Hui Chen, M. Nakai, Y. Sentoku, Y. Arikawa, H. Azechi, S. Fujioka, C. Keane, S. Kojima, W. Goldstein, B. R. Maddox, N. Miyanaga, T. Morita, T. Nagai, H. Nishimura, T. Ozaki, J. Park, Y. Sakawa, H. Takabe, G. Williams, Z. Zhang

NEW JOURNAL OF PHYSICS 15 2013.6

We report new results from the intense laser target interaction experiment that produces relativistic electron-positron pairs. Laser to electron energy transfer, inferred using x-ray and neutron measurements, was found to be consistent with the measured positrons. To increase the number of positrons, one needs to deliver a greater number of relativistic electrons from the laser-plasma interaction to the high Z gold target. A large preplasma was found to have a negative impact for this purpose, while the laser could produce hotter electrons in such preplasma. The peak energy shift in the positron spectrum is confirmed as the post-acceleration in the sheath potential behind the target. The results were supported by a collisional one-dimensional particle-in-cell code. This experiment was performed using the high-power LFEX laser at the Institute of Laser Engineering at Osaka University using a suite of diagnostics measuring electrons, positrons, x-rays and neutrons from the laser-target interaction at the relativistic regime.

Pr or Ce-doped, fast-response and low-afterglow cross-section-enhanced scintillator with Li-6 for down-scattered neutron originated from laser fusion Reviewed

Kozue Watanabe, Yasunobu Arikawa, Kohei Yamanoi, Marilou Cadatal-Raduban, Takahiro Nagai, Masahiro Kouno, Kohei Sakai, Tomoharu Nazakato, Toshihiko Shimizu, Nobuhiko Sarukura, Mitsuo Nakai, Takayoshi Norimatsu, Hiroshi Azechi, Akira Yoshikawa, Takahiro Murata, Shigeru Fujino, Hideki Yoshida, Nobuhiko Izumi, Nakahiro Satoh, Hirofumi Kan

JOURNAL OF CRYSTAL GROWTH 362 288 - 290 2013.1

We explore the potential of Pr- or Ce-doped 20Al(PO3)(3)-80LiF (APLF80+3Pr or +3Ce) scintillator to observe the lower edge of down-scattered neutron and discriminate fusion originated neutron from strong X-ray signals. APLF80+3Pr or +3Ce scintillator exhibits considerably fast decay profiles and negligible slow-decay components. Using these newly developed APLF80+3Pr or +3Ce scintillators, we have successfully observed fusion-originated neutron signal in the midst of strong X-ray-excited fluorescence in an integrated experiment using our 10 kJ class GEKKO XII Nd-glass laser system. A sophisticated neutron detection system using APLF80+3Pr or 3Ce will be used for the first fast ignition experiment. (C) 2011 Elsevier BY. All rights reserved.

Development of time-of-flight neutron detector with fast-decay and low-afterglow scintillator for fast ignition experiment Reviewed

T. Nagai, Y. Arikawa, H. Hosoda, Y. Ioka, A. Hasegawa, K. Wada, S. Takaoku, M. Takata, K. Noritake, Y. Minami, K. Watanabe, K. Yamanoi, H. Nakamura, T. Watari, M. Cadatal-Raduban, T. Shimizu, N. Sarukura, M. Nakai, T. Norimatsu, H. Azechi

IFSA 2011 - SEVENTH INTERNATIONAL CONFERENCE ON INERTIAL FUSION SCIENCES AND APPLICATIONS 59 2013

A fast-decay and low-afterglow liquid scintillator was developed for the fast ignition experiment at the Institute of Laser Engineering (ILE). The liquid scintillator was coupled to a gated photomultiplier (PMT), and the gating performance under high-intensity gamma-rays was experimentally checked. In 2010, a detector with a high detection efficiency of 10(-4) was developed and installed in this experiment. The neutron yield in the fast heating experiment was successfully measured using this detector.

Implosion and heating experiments of fast ignition targets by Gekko-XII and LFEX lasers Reviewed

H. Shiraga, S. Fujioka, M. Nakai, T. Watari, H. Nakamura, Y. Arikawa, H. Hosoda, T. Nagai, M. Koga, H. Kikuchi, Y. Ishii, T. Sogo, K. Shigemori, H. Nishimura, Z. Zhang, M. Tanabe, S. Ohira, Y. Fujii, T. Namimoto, Y. Sakawa, O. Maegawa, T. Ozaki, K. A. Tanaka, H. Habara, T. Iwawaki, K. Shimada, M. Key, P. Norreys, J. Pasley, H. Nagatomo, T. Johzaki, A. Sunahara, M. Murakami, H. Sakagami, T. Taguchi, T. Norimatsu, H. Homma, Y. Fujimoto, A. Iwamoto, N. Miyanaga, J. Kawanaka, T. Kanabe, T. Jitsuno, Y. Nakata, K. Tsubakimoto, K. Sueda, R. Kodama, K. Kondo, N. Morio, S. Matsuo, T. Kawasaki, K. Sawai, K. Tsuji, H. Murakami, N. Sarukura, T. Shimizu, K. Mima, H. Azechi

IFSA 2011 - SEVENTH INTERNATIONAL CONFERENCE ON INERTIAL FUSION SCIENCES AND APPLICATIONS 59 2013

The FIREX-1 project, the goal of which is to demonstrate fuel heating up to 5 keV by fast ignition scheme, has been carried out since 2003 including construction and tuning of LFEX laser and integrated experiments. Implosion and heating experiment of Fast Ignition targets have been performed since 2009 with Gekko-XII and LFEX lasers. A deuterated polystyrene shell target was imploded with the 0.53-mu m Gekko-XII, and the 1.053-mu m beam of the LFEX laser was injected through a gold cone attached to the shell to generate hot electrons to heat the imploded fuel plasma. Pulse contrast ratio of the LFEX beam was significantly improved. Also a variety of plasma diagnostic instruments were developed to be compatible with harsh environment of intense hard x-rays (gamma rays) and electromagnetic pulses due to the intense LFEX beam on the target. Large background signals around the DD neutron signal in time-of-flight record of neutron detector were found to consist of neutrons via (gamma, n) reactions and scattered gamma rays. Enhanced neutron yield was confirmed by carefully eliminating such backgrounds. Neutron enhancement up to 3.5 x 10(7) was observed. Heating efficiency was estimated to be 10-20% assuming a uniform temperature rise model.

Implosion and heating experiments of fast ignition targets by Gekko-XII and LFEX lasers Reviewed

EPJ Web of Conferences 59 2013

The FIREX-1 project, the goal of which is to demonstrate fuel heating up to 5 keV by fast ignition scheme, has been carried out since 2003 including construction and tuning of LFEX laser and integrated experiments. Implosion and heating experiment of Fast Ignition targets have been performed since 2009 with Gekko-XII and LFEX lasers. A deuterated polystyrene shell target was imploded with the 0.53- μm Gekko-XII, and the 1.053- μm beam of the LFEX laser was injected through a gold cone attached to the shell to generate hot electrons to heat the imploded fuel plasma. Pulse contrast ratio of the LFEX beam was significantly improved. Also a variety of plasma diagnostic instruments were developed to be compatible with harsh environment of intense hard x-rays (γ rays) and electromagnetic pulses due to the intense LFEX beam on the target. Large background signals around the DD neutron signal in time-of-flight record of neutron detector were found to consist of neutrons via (γ,n) reactions and scattered gamma rays. Enhanced neutron yield was confirmed by carefully eliminating such backgrounds. Neutron enhancement up to 3.5 × 107 was observed. Heating efficiency was estimated to be 10-20% assuming a uniform temperature rise model. © Owned by the authors, published by EDP Sciences, 2013.

Multichannel down-scattered neutron detector for areal density measurement

Y. Arikawa, H. Hosoda, T. Nagai, K. Watanabe, K. Yamanoi, M. Cadatal-Raduban, T. Shimizu, N. Sarukura, M. Nakai, T. Norimatsu, H. Azechi, N. Izumi, T. Murata, T. Suyama, A. Yoshikawa, K. Kamada, Y. Usuki, N. Satoh, H. Kan

EPJ Web of Conferences 59 UNSP 13011 2013

A down-scattered neutron detector operating in the multichannel counting mode was developed for areal density (ρR) measurement. Equipped with a newly developed 6Li glass scintillator (APLF80), the detector was tested in a fusion experiment at the GEKKO XII facility, Osaka University, Osaka, Japan. For a low-ρR fusion shot, the detector clearly discriminated the γ-rays, primary neutrons, γ-rays produced via (n, γ) reactions from the target chamber, and neutrons scattered by the target chamber. Furthermore, the observed signal was in good agreement with predictions made by Monte Carlo simulation. © Owned by the authors, published by EDP Sciences, 2013.

Recent progress of fuel layering study for FIREX cryogenic target Reviewed

A. Iwamoto, T. Fujimura, M. Nakai, T. Norimatsu, H. Shiraga, H. Azechi, Y. Fujimoto, S. Machi, H. Sakagami

IFSA 2011 - SEVENTH INTERNATIONAL CONFERENCE ON INERTIAL FUSION SCIENCES AND APPLICATIONS 59 2013

Fast-Response and Low-Afterglow Cerium-Doped Lithium 6 Fluoro-Oxide Glass Scintillator for Laser Fusion-Originated Down-Scattered Neutron Detection Reviewed

Takahiro Murata, Yasunobu Arikawa, Kozue Watanabe, Kohei Yamanoi, Marilou Cadatal-Raduban, Takahiro Nagai, Masahiro Kouno, Kohei Sakai, Tomoharu Nakazato, Toshihiko Shimizu, Nobuhiko Sarukura, Mitsuo Nakai, Takayoshi Norimatsu, Hiroaki Nishimura, Hiroshi Azechi, Akira Yoshikawa, Shigeru Fujino, Hideki Yoshida, Nobuhiko Izumi, Nakahiro Sato, Hirofumi Kan

IEEE TRANSACTIONS ON NUCLEAR SCIENCE 59 ( 5 ) 2256 - 2259 2012.10

The photonuclear neutron and gamma-ray backgrounds in the fast ignition experiment Reviewed

Y. Arikawa, T. Nagai, H. Hosoda, Y. Abe, S. Kojima, S. Fujioka, N. Sarukura, M. Nakai, H. Shiraga, T. Ozaki, H. Azechi

Review of Scientific Instruments 83 ( 10 ) 10D909 2012.10

In the fast-ignition scheme, very hard x-rays (hereinafter referred to as γ-rays) are generated by Bremsstrahlung radiation from fast electrons. Significant backgrounds were observed around the deuterium-deuterium fusion neutron signals in the experiment in 2010. In this paper the backgrounds were studied in detail, based on Monte Carlo simulations, and they were confirmed to be γ-rays from the target, scattered γ-rays from the experimental bay walls γ'-rays), and neutrons generated by (γ, n) reactions in either the target vacuum chamber or the diagnostic instruments (γ-n neutrons). © 2012 American Institute of Physics.

Integrated experiments of fast ignition targets by Gekko-XII and LFEX lasers Reviewed

H. Shiraga, S. Fujioka, M. Nakai, T. Watari, H. Nakamura, Y. Arikawa, H. Hosoda, T. Nagai, M. Koga, H. Kikuchi, Y. Ishii, T. Sogo, K. Shigemori, H. Nishimura, Z. Zhang, M. Tanabe, S. Ohira, Y. Fuji, T. Namimoto, Y. Sakawa, O. Maegawa, T. Ozaki, K. A. Tanaka, H. Habara, T. Iwawaki, K. Shimada, H. Nagatomo, T. Johzaki, A. Sunahara, M. Murakami, H. Sakagami, T. Taguchi, T. Norimatsu, H. Homma, Y. Fujimoto, A. Iwamoto, N. Miyanaga, J. Kawanaka, T. Jitsuno, Y. Nakata, K. Tsubakimoto, K. Sueda, N. Morio, S. Matsuo, T. Kawasaki, K. Sawai, K. Tsuji, H. Murakami, T. Kanabe, K. Kondo, R. Kodama, N. Sarukura, T. Shimizu, K. Mima, H. Azechi

HIGH ENERGY DENSITY PHYSICS 8 ( 3 ) 227 - 230 2012.9

Implosion and heating experiments at the Institute of Laser Engineering, Osaka University on Fast Ignition (FI) targets for the FIREX-1 project have been performed with Gekko-XII laser for implosions and LFEX laser for heating. We tried to reduce the prepulse level in the LFEX laser system and have improved the plasma diagnostics to observe the plasma in the harsh hard X-ray envilonment. A plastic (CD) shell target, 7-mu m thick and 500 mu m in diameter with a hollow gold cone was used in this experiment to guide the short-pulse laser at the time of the maximum compression. The shell target was imploded with 9 or 12 beams of Gekko-XII laser (527 nm) with energy of 300 J/beam in a 1.5 ns pulse. Two of the four LFEX laser (1053 nm) beams were injected into the inside bottom of the cone with an energy up to 0.7 kJ/beam in a 1.5 Ps pulse at the time around the maximum implosion. We have observed neutron enhancement up to 3.5 x 10(7) with total heating energy of 300 J, which is higher than the yield obtained in the previous experiment in 2002 [R. Kodama et al. Nature 418,933 (2002)]. We found the estimated heating efficiency is at a level of 10-20%. Fuel heating to 5 keV is expected when the full output of LFEX is used. (c) 2012 Elsevier B.V. All rights reserved.

Fast ignition integrated experiments with Gekko and LFEX lasers Reviewed

H. Shiraga, S. Fujioka, M. Nakai, T. Watari, H. Nakamura, Y. Arikawa, H. Hosoda, T. Nagai, M. Koga, H. Kikuchi, Y. Ishii, T. Sogo, K. Shigemori, H. Nishimura, Z. Zhang, M. Tanabe, S. Ohira, Y. Fujii, T. Namimoto, Y. Sakawa, O. Maegawa, T. Ozaki, K. Tanaka, H. Habara, T. Iwawaki, K. Shimada, H. Nagatomo, T. Johzaki, A. Sunahara, M. Murakami, H. Sakagami, T. Taguchi, T. Norimatsu, H. Homma, Y. Fujimoto, A. Iwamoto, N. Miyanaga, J. Kawanaka, T. Jitsuno, Y. Nakata, K. Tsubakimoto, N. Morio, T. Kawasaki, K. Sawai, K. Tsuji, H. Murakami, T. Kanabe, K. Kondo, N. Sarukura, T. Shimizu, K. Mima, H. Azechi

PLASMA PHYSICS AND CONTROLLED FUSION 53 ( 12 ) 2011.12

Based on the successful result of fast heating of a shell target with a cone for heating beam injection at Osaka University in 2002 using the PW laser (Kodama et al 2002 Nature 418 933), the FIREX-1 project was started in 2004. Its goal is to demonstrate fuel heating up to 5 keV using an upgraded heating laser beam. For this purpose, the LFEX laser, which can deliver an energy up to 10 kJ in a 0.5-20 ps pulse at its full spec, has been constructed in addition to the Gekko-XII laser system at the Institute of Laser Engineering, Osaka University. It has been activated and became operational since 2009. Following the previous experiment with the PW laser, upgraded integrated experiments of fast ignition have been started using the LFEX laser with an energy up to 1 kJ in 2009 and 2 kJ in 2010 in a 1-5 ps 1.053 mu m pulse. Experimental results including implosion of the shell target by Gekko-XII, heating of the imploded fuel core by LFEX laser injection, and increase of the neutron yield due to fast heating compared with no heating have been achieved. Results in the 2009 experiment indicated that the heating efficiency was 3-5%, much lower than the 20-30% expected from the previous 2002 data. It was attributed to the very hot electrons generated in a long scale length plasma in the cone preformed with a prepulse in the LFEX beam. The prepulse level was significantly reduced in the 2010 experiment to improve the heating efficiency. Also we have improved the plasma diagnostics significantly which enabled us to observe the plasma even in the hard x-ray harsh environment. In the 2010 experiment, we have observed neutron enhancement up to 3.5 x 10(7) with total heating energy of 300 J on the target, which is higher than the yield obtained in the 2009 experiment and the previous data in 2002. We found the estimated heating efficiency to be at a level of 10-20%. 5 keV heating is expected at the full output of the LFEX laser by controlling the heating efficiency.

LEAKAGE CONTROL OF TRITIUM THROUGH HEAT CYCLES OF CONCEPTUAL-DESIGN, LASER-FUSION REACTOR KOYO-F Reviewed

T. Norimatsu, H. Saika, H. Homma, M. Nakai, S. Fukada, A. Sagara, H. Azechi

FUSION SCIENCE AND TECHNOLOGY 60 ( 3 ) 893 - 896 2011.10

To reduce the tritium permeation from the primary liquid metal loop to the secondary water loop, a heat exchanger concept that incorporates small diameter tubes containing an oxidizer was proposed. An inert gas containing a small amount of oxidizer flows in the small tubes oxiding tritium that comes from the primary liquid metal coolant. The tritiated water is sent to a tritium recovery system minimizing leakage to the secondary water loop. Our evaluation results indicated that the tritium leakage through the heat exchanger was reduced to 1/10(5) with an acceptable increase in the size of the heat exchanger.

Present states and future prospect of fast ignition realization experiment (FIREX) with Gekko and LFEX Lasers at ILE Reviewed

Mayuko Koga, Y. Arikawa, H. Azechi, Y. Fujimoto, S. Fujioka, H. Habara, Y. Hironaka, H. Homma, H. Hosoda, T. Jitsuno, T. Johzaki, J. Kawanaka, R. Kodama, K. Mima, N. Miyanaga, M. Murakami, H. Nagatomo, M. Nakai, Y. Nakata, H. Nakamura, H. Nishimura, T. Norimatsu, Y. Sakawa, N. Sarukura, K. Shigemori, H. Shiraga, T. Shimizu, H. Takabe, M. Tanabe, K. A. Tanaka, T. Tanimoto, T. Tsubakimoto, T. Watari, A. Sunahara, M. Isobe, A. Iwamoto, T. Mito, O. Motojima, T. Ozaki, H. Sakagami, T. Taguchi, Y. Nakao, H. Cai, M. Key, P. Norreys, J. Pasley

NUCLEAR INSTRUMENTS & METHODS IN PHYSICS RESEARCH SECTION A-ACCELERATORS SPECTROMETERS DETECTORS AND ASSOCIATED EQUIPMENT 653 ( 1 ) 84 - 88 2011.10

The fast ignition realization experiment (FIREX) project is progressing. The new short pulse laser system, LFEX laser, has been completely assembled and one of the four beamlets is now in operation. A fast-ignition experiment was performed using this single short pulse combined with the Gekko XII implosion laser. The energy of the GXII implosion laser was about 2 kJ and the pulse width was 1.5 ns. The energy of the LFEX laser was increased upto 800 J and two pulse durations 5 and 1.6 ps were compared. Targets were deuterated plastic shells with gold cones. It was found that the neutron yield was increased by a factor of 30 as a result of the fast electron-induced heating in LFEX 1.6 ps shot. The estimated coupling efficiency between the LFEX laser pulse and the compressed fuel was low (less than 5%). This may be due to pre-plasma formed by light arriving at the target before the main laser pulse. Further investigations and attempts to overcome these problems are now in progress. (C) 2011 Elsevier B.V. All rights reserved.

Fast-response, Low-Afterglow 4,4 '''-Bis[(2-butyloctyl)oxy]-1,1 ':4 ',1 '':4 '',1 '''-quarterphenyl Dye-Based Liquid Scintillator for High-Contrast Detection of Laser Fusion-Generated Neutrons Reviewed

Takahiro Nagai, Yusuke Ioka, Ai Hasegawa, Kazuhiro Wada, Shingo Takaoku, Masatoshi Takata, Katsuya Noritake, Yuki Minami, Kozue Watanabe, Kohei Yamanoi, Yasunobu Arikawa, Hirokazu Hosoda, Hirotaka Nakamura, Takeshi Watari, Marilou Cadatal-Raduban, Mayuko Koga, Toshihiko Shimizu, Nobuhiko Sarukura, Hiroyuki Shiraga, Mitsuo Nakai, Takayoshi Norimatsu, Hiroshi Azechi

JAPANESE JOURNAL OF APPLIED PHYSICS 50 ( 8 ) 2011.8

4,4'''-Bis[(2-butyloctyl)oxy]-1,1':4',1 '':4 '',1'''-quaterphenyl (BBQ) dye dissolved in xylene and enriched with oxygen is shown to exhibit the characteristics of an ideal neutron scintillator for time-of-flight (TOF) measurement in a laser fusion experiment. Initial results from excitation with 290-nm pulses show that it has a 0.76-ns fast decay component and a negligible slow decay component or afterglow. By using this scintillator for TOF measurement, we have successfully discriminated between nuclear fusion-generated neutrons and X-rays. This would dramatically improve neutron diagnostics in fast ignition experiments where neutrons have to be detected in the presence of an intense X-ray burst. (C) 2011 The Japan Society of Applied Physics

Laser-shock compression and Hugoniot measurements of liquid hydrogen to 55 GPa Reviewed

T. Sano, N. Ozaki, T. Sakaiya, K. Shigemori, M. Ikoma, T. Kimura, K. Miyanishi, T. Endo, A. Shiroshita, H. Takahashi, T. Jitsui, Y. Hori, Y. Hironaka, A. Iwamoto, T. Kadono, M. Nakai, T. Okuchi, K. Otani, K. Shimizu, T. Kondo, R. Kodama, K. Mima

PHYSICAL REVIEW B 83 ( 5 ) 2011.2

The principal Hugoniot for liquid hydrogen was obtained up to 55 GPa under laser-driven shock loading. The pressure and density of compressed hydrogen were determined by impedance matching to a quartz standard. The shock temperature was independently measured from the brightness of the shock front. Hugoniot data of hydrogen provide a good benchmark to modern theories of condensed matter. The initial number density of liquid hydrogen is lower than that for liquid deuterium, and this results in shock-compressed hydrogen having a higher compression and higher temperature than deuterium at the same shock pressure.

Optical and scintillation properties of Pr-doped Li-glass for neutron detection in inertial confinement fusion process Reviewed

Akihiro Fukabori, Takayuki Yanagida, Valery Chani, Federico Moretti, Jan Pejchal, Yuui Yokota, Noriaki Kawaguchi, Kei Kamada, Ken-ichi Watanabe, Takahiro Murata, Yasunobu Arikawa, Kohei Yamanoi, Toshihiko Shimizu, Nobuhiko Sarukura, Mitsuo Nakai, Takayoshi Norimatsu, Hiroshi Azechi, Shigeru Fujino, Hideki Yoshida, Akira Yoshikawa

JOURNAL OF NON-CRYSTALLINE SOLIDS 357 ( 3 ) 910 - 914 2011.2

Optical and scintillation properties of Pr-doped Li-glass, 20Al(PO3)(3)-80LiF:Pr 3%, have been studied for applications in neutron detection systems. Based on optical transmission and reflectivity, the absorption coefficient and refractive index were calculated from the Beer Lambert law. The absorption edge was apparently shifted to the longer wavelength from 160 nm to 240 nm due to 4f -> 5d transitions of Pr ions. The strong absorption peaks of praseodymium 4f -> 4f transitions were observed from 420 nm to 500 nm and around 590 nm. The radio-luminescence spectrum excited by Am-241 5.5 MeV a source was measured. Strong emission peaks were observed around 250 nm. The alpha-ray excited pulse height spectrum and decay kinetics were also examined. Light yield was estimated to be 400 +/- 40 photons/5.5 MeV a and the main component of the decay time was evaluated to be about 12 ns. Furthermore, the pulse height spectrum of the glass excited by 252Cf neutrons was also measured, and the light yield was estimated to be 140 +/- 10 photons/neutron. (C) 2010 Elsevier B.V. All rights reserved.

RECENT DEVELOPMENTS IN FABRICATION OF NEW CONCEPTUAL GOLD CONE AND MACHINING OF POLYSTYRENE SHELL FOR FAST IGNITION TARGET Reviewed

H. Homma, H. Kadota, H. Hosokawa, M. Nagata, T. Fujimura, K. Nagai, M. Nakai, T. Norimatsu, H. Azechi

FUSION SCIENCE AND TECHNOLOGY 59 ( 1 ) 276 - 278 2011.1

Recent developments of several key issues for fabrication techniques of cone and shell target for the first phase of the Fast Ignition Realization Experiment (FIREX-I) project at the Institute of Laser Engineering, Osaka University, are described in this paper. The most important modification of the target design is a double cone, and a new fabrication technique has been developed. Although the error of assembling the cones is still several microns, the first prototype of a double-cone target with a vacuum gap of 20 mu m was successfully provided for the preliminary experiment. Additionally, Ti:sapphire laser machining was used to bore a hole in the polystyrene shell.

Optical properties and structure of Pr3+-doped Al(PO 3)3-LiF glasses as scattered neutron scintillator for nuclear fusion diagnostics Reviewed

T. Murata, S. Fujino, H. Yoshida, Y. Arikawa, T. Nakazato, T. Shimizu, N. Sarukura, M. Nakai, T. Norimatsu, H. Azechi, K. Kamada, Y. Usuki, T. Suyama, A. Yoshikawa, N. Sato, H. Kan

IOP Conference Series: Materials Science and Engineering 18 ( 8 ) 112006 2011

Scattered neutron diagnostics is an indispensable tool for both inertial confinement and magnetic confinement fusion research. For this purpose, a fast-response neutron scintillator with a high cross section for scattered neutrons is strongly required. Recently, based on our material design strategy, we have successfully developed the fast response time Pr3+-doped 20Al(PO3)3-80LiF glass scintillator for scattered neutron originated from inertial confinement fusion. The matrix glass 20Al(PO 3)3-80LiF shows good glass forming ability, chemical durability and transparency in the deep ultraviolet region. The purpose of this work is to investigate the glass structure of 20Al(PO3) 3-80LiF glasses using Raman spectroscopy and to discuss the relationship between physical and scintillation properties and glass structure. © 2011 Ceramic Society of Japan.

Down-scattered neutron imaging detector for areal density measurement of inertial confinement fusion Reviewed

Y. Arikawa, K. Yamanoi, T. Nakazato, E. S. Estacio, T. Shimizu, N. Sarukura, M. Nakai, H. Hosoda, T. Norimatsu, Y. Hironaka, H. Azechi, N. Izumi, T. Murata, S. Fujino, H. Yoshida, K. Kamada, Y. Usuki, T. Suyama, A. Yoshikawa, N. Satoh, H. Kan

Review of Scientific Instruments 81 ( 10 ) 10D303 2010.10

A custom developed 6Li glass scintillator (APLF80+3Pr) for down-scattered neutron diagnostics in inertial confinement fusion experiments is presented. 6Li provides an enhanced sensitivity for down-scattered neutrons in DD fusion and its experimentally observed 5-6 ns response time fulfills the requirement for down-scattered neutron detectors. A time-of-flight detector operating in the current mode using the APLF80+3Pr was designed and its feasibility observing down-scattered neutrons was demonstrated. Furthermore, a prototype design for a down-scattered neutron imaging detector was also demonstrated. This material promises viability as a future down-scattered neutron detector for the National Ignition Facility. © 2010 American Institute of Physics.

Note: Light output enhanced fast response and low afterglow Li-6 glass scintillator as potential down-scattered neutron diagnostics for inertial confinement fusion Reviewed

Yasunobu Arikawa, Kohei Yamanoi, Takahiro Nagai, Kozue Watanabe, Masahiro Kouno, Kohei Sakai, Tomoharu Nakazato, Toshihiko Shimizu, Marilou Raduban Cadatal, Elmer Surat Estacio, Nobuhiko Sarukura, Mitsuo Nakai, Takayoshi Norimatsu, Hiroshi Azechi, Takahiro Murata, Shigeru Fujino, Hideki Yoshida, Nobuhiko Izumi, Nakahiro Satoh, Hirofumi Kan

REVIEW OF SCIENTIFIC INSTRUMENTS 81 ( 10 ) 2010.10

The characteristics of an APLF80+3Ce scintillator are presented. Its sufficiently fast decay profile, low afterglow, and an improved light output compared to the recently developed APLF80+3Pr, were experimentally demonstrated. This scintillator material holds promise for applications in neutron imaging diagnostics at the energy regions of 0.27 MeV of DD fusion down-scattered neutron peak at the world's largest inertial confinement fusion facilities such as the National Ignition Facility and the Laser Megajoule. (C) 2010 American Institute of Physics. [doi:10.1063/1.3488460]

Custom-designed scintillator for laser fusion diagnostics - Pr3+-doped fluoro-phosphate lithium glass scintillator Reviewed

Yasunobu Arikawa, Kohei Yamanoi, Tomoharu Nakazato, Elmer Surat Estacio, Toshihiko Shimizu, Nobuhiko Sarukura, Mitsuo Nakai, Takayoshi Norimatsu, Youichirou Hironaka, Hiroshi Azechi, Takahiro Murata, Shigeru Fujino, Hideki Yoshida, Kei Kamada, Yoshiyuki Usuki, Toshihisa Suyama, Akira Yoshikawa, Nakahiro Satoh, Hirohumi Kan

OPTICAL MATERIALS 32 ( 10 ) 1393 - 1396 2010.8

A novel custom-developed scintillator for laser fusion diagnostics is reported. With the aim of diagnosing scattered neutrons from the imploded high-density fusion plasma, a fast response lithium-6 glass scintillator has been developed. Praseodymium, instead of the more widely-used cerium was chosen as the dopant. Sufficiently fast luminescence lifetime for scattered neutron diagnostics (<20 ns) was experimentally observed, and the feasibility was successfully shown in laser-fusion experiments at the GEKKO XII facility of the Institute of Laser Engineering, Osaka University. (C) 2010 Elsevier B.V. All rights reserved.

Custom-Designed Fast-Response Praseodymium-Doped Lithium 6 Fluoro-Oxide Glass Scintillator With Enhanced Cross-Section for Scattered Neutron Originated From Inertial Confinement Fusion Reviewed

Takahiro Murata, Shigeru Fujino, Hideki Yoshida, Yasunobu Arikawa, Tomoharu Nakazato, Toshihiko Shimizu, Nobuhiko Sarukura, Mitsuo Nakai, Takayoshi Norimatsu, Hiroshi Azechi, Kei Kamada, Yoshiyuki Usuki, Toshihisa Suyama, Akira Yoshikawa, Nakahiro Sato, Hirofumi Kan

IEEE TRANSACTIONS ON NUCLEAR SCIENCE 57 ( 3 ) 1426 - 1429 2010.6

Scintillation properties of Pr(3+)-doped 20Al(PO(3))(3)-80 LiF glasses melted in N(2) were investigated to seek a candidate for a scattered neutron scintillator in nuclear fusion diagnostics. The fluorescence lifetime of the sample with 217 nm ultraviolet femtosecond pulse excitation was measured to be 19.5 ns. More importantly, the fluorescence lifetime with alpha particles from (241)Am radioisotope excitation was determined to be 6.7 ns. Based on our material design strategy, we have successfully developed the fast response time praseodymium-doped (6)Li glass scintillator for scattered neutron diagnostics.

Measurement of preheating due to radiation and nonlocal electron heat transport in laser-irradiated targets Reviewed

K. Otani, K. Shigemori, T. Kadono, Y. Hironaka, M. Nakai, H. Shiraga, H. Azechi, K. Mima, N. Ozaki, T. Kimura, K. Miyanishi, R. Kodama, T. Sakaiya, A. Sunahara

PHYSICS OF PLASMAS 17 ( 3 ) 2010.3

This paper reports an experimental study on preheating of laser-irradiated targets. We performed temperature measurements at the rear surface of laser-irradiated targets under conditions of two different laser wavelengths (0.35 or 0.53 mu m) and several intensities (2 x 10(13) -1 x 10(14) W/cm(2)) in order to verify an effect of radiation and nonlocal electron heat transport. The preheating temperature was evaluated by observing self-emission, reflectivity, and expansion velocity at the rear surface of planar polyimide foils. The experimental results show that the x-ray radiation is dominant for preheating for 0.35-mu m laser irradiation, but contribution of nonlocal electron heat transport is not negligible for 0.53-mu m laser irradiation conditions. (C) 2010 American Institute of Physics. [doi:10.1063/1.3372099]

Experimental investigation to demonstrate Impact Fast Ignition scheme Reviewed

T. Watari, H. Azechi, M. Nakai, Y. Hironaka, T. Sakaiya, H. Nakamura, H. Shiraga, K. Shigemori, H. Hosoda, Y. Arikawa, H. Homma, T. Norimatsu, M. Murakami, T. Jhozaki, M. Karasik, J. Gardner, J. Bates, D. Colombant, J. Weber, Y. Aglitsky, S. Obenschain

SIXTH INTERNATIONAL CONFERENCE ON INERTIAL FUSION SCIENCES AND APPLICATIONS, PARTS 1-4 244 2010

We have proposed a new ignition scheme of Fast Ignition, called "Impact Fast Ignition (IFI)", in which a compressed fuel is ignited by impact collision of a fragment of separately imploded fuel. We performed integrated experiments on impact ignition, in which a portion of a deuterated polystyrene (CD) shell was accelerated to about 600 km/s and was collided with precompressed CD fuel. The shell was imploded using 9 beams and the impactor was accelerated using 3 beams of the GEKKO XII laser system. The laser energy was 350 J per beam. The kinetic energy of the impactor was efficiently converted into thermal energy generating a temperature of about 1.8 keV., Observed maximum neutron yield was 2x10(6). This yield was 80 times as large as that without impactor. We will present the experimental details and results, demonstrating the high potential of impact ignition for fusion energy production.

Industrial Applications of Laser Neutron Source Reviewed

S. Nakai, K. Mima, Y. Kato, K. Tanaka, Y. Ikeda, H. Azechi, K. Miyanaga, M. Nakai, M. Perlado, R. Gonzalez Arrabal

SIXTH INTERNATIONAL CONFERENCE ON INERTIAL FUSION SCIENCES AND APPLICATIONS, PARTS 1-4 244 2010

The industrial applications of the intense neutron source have been widely explored because of the unique features of the neutron-matter interaction. Usually, intense neutron sources are assembled with fission reactors or high energy ion accelerators. The big size and high cost of these systems are the bottle neck to promote the industrial applications of intense neutrons. In this paper, we propose the compact laser driven neutron source for the industrial application. As the first step of our project for the versatile applications of laser driven neutron source, Li-neutron and/or Li-proton interactions have been investigated for the application to the development of Li battery.

Hugoniot and temperature measurements of liquid hydrogen by laser-shock compression Reviewed

SIXTH INTERNATIONAL CONFERENCE ON INERTIAL FUSION SCIENCES AND APPLICATIONS, PARTS 1-4 244 2010

Hydrogen at high pressure in the fluid state is of great interest for target design of inertial confinement fusion and understanding the interior structure of gas giant planets. In this work, we successfully obtained the Hugoniot data for liquid hydrogen up to 55 GPa under laser-driven shock loading using impedance matching to a quartz standard. The shocked temperature was determined simultaneously by the brightness temperature. The compression and temperature along the principal Hugoniot are in good agreement with theoretical models. High reflectivity of hydrogen was observed at 40 GPa, which suggests the fluid becomes conducting

High-speed monochromatic x-ray imager for electron temperature mapping of fast igniter plasmas Reviewed

Minoru Tanabe, Takashi Fujiwara, Shinsuke Fujioka, Nobuo Hayashi, Hiroaki Nishimura, Takeshi Fujimura, Mitsuo Nakai, Keiji Nagai, Hirofumi Homma, Hiroyuki Shiraga, Takayoshi Norimatsu, Hiroshi Azechi, Kunioki Mima

SIXTH INTERNATIONAL CONFERENCE ON INERTIAL FUSION SCIENCES AND APPLICATIONS, PARTS 1-4 244 2010

We report on experiments aimed at obtaining laser-imploded core plasma temperature maps using two color, monochromatic x-ray imager. This instrument uses two toroidally bent Bragg crystals and a high-speed sampling imager to provide spatial resolution of 25 mu m, temporal resolution of 20 ps, and spectral resolution over 200, simultaneously. Using a deuterated plastic shell target filled with CHClF(2) gas, time-resolved monochromatic x-ray images in the Cl-He(beta) and Cl-Ly(beta) were successfully obtained.

Laser Machining for Fabrication of Targets used in the FIREX-I project Reviewed

T. Fujimura, M. Nakai, A. Iwamoto, N. Hayashi, M. Tanabe, Yu. Izawa, K. Nagai, H. Homma, H. Nishimura, T. Norimatsu, H. Azechi

SIXTH INTERNATIONAL CONFERENCE ON INERTIAL FUSION SCIENCES AND APPLICATIONS, PARTS 1-4 244 2010

This paper reports on way to fabricate a gas-tight targets dedicated for the first stage of Fast Ignition Realization Experiment (FIREX-I) at the Institute of Laser Engineering (ILE), Osaka University. It was found that a Ti;sapphire laser machining can be used to fabricate the target. The performance of the laser machining using a fs Ti; sapphire laser was examined on shell materials. The conditions for accurate machining were determined. Michelson interferometer with two different wavelengths which imitates a white light interferometer is an excellent tool for confirming the gas-tightness of the target after assembly.

A SCATTERED-NEUTRON DETECTOR FOR AREAL DENSITY MEASUREMENT Reviewed

Y. Arikawa, T. Murata, S. Fujino, H. Yoshida, K. Yamanoi, T. Nakazato, T. Shimizu, N. Sarukura, M. Nakai, T. Norimatsu, H. Azechi, K. Kamada, Y. Usuki, T. Suyama, A. Yoshikawa, N. Satoh, H. Kan

SIXTH INTERNATIONAL CONFERENCE ON INERTIAL FUSION SCIENCES AND APPLICATIONS, PARTS 1-4 244 2010

Experimental results are presented on the neutron scintillating properties of a custom-designed Praseodymium-doped Lithium-6 glass for a new deuterium-deuterium (DD) fusion scattered-neutron detector. Luminescence was observed at 278 nm-wavelength, and time-resolved measurement yielded similar to 5.4 ns decay time for neutron excitation. Actual time-of-flight data in laser fusion experiments at the GEKKO XII facility at the Institute of Laser Engineering (ILE), Osaka University reveal that it can clearly discriminate fusion primary-neutrons from the x-ray signals. This material promises the realization of more accurate DD fusion scattered-neutron diagnostics. Design work for a scattered-neutron detector is being conducted for the Fast Ignition Realization Experiment (FIRE-X) at ILE.

Laser surface inspections: Fundamentals and applications to monitor inner surface conditions of nuclear fusion reactor chambers Reviewed

Koichi Kasuya, S. Ozawa, T. Norimatsu, H. Azechi, K. Mima, S. Nakai, S. Suzuki, B. Budner, W. Mroz, N. Kasuya, W. Kasuya, Kei Kasuya, Y. Izawa, H. Furukawa, Y. Shimada, T. Yamanaka, M. Nakai, K. Nagai, K. Yokoyama, K. Ezato, M. Enoeda, M. Akiba, A. Prokopiuk

Proceedings of SPIE - The International Society for Optical Engineering 7751 2010

The most recent fundamental research results to investigate surface erosions of nuclear fusion candidate chamber materials are described in short. We used a commercial surface profiler with a red semiconductor laser. Various material surfaces ablated and eroded by a rather short pulse electron beam and a short pulse ArF laser light were measured with this surface profiler and the associated three-dimensional analysis software. Threshold input levels for various sample surface erosions with electron and laser beams were clearly decided for the first time with our new method in this article. After the above fundamental results were gathered, the methods to inspect inner surface conditions of nuclear fusion reactor chambers were newly proposed with various kinds of laser displacement sensors. The first one is the erosion monitor with the above profiler, and the second one is the laser induced ultrasonic wave detection method to inspect deeper surface layers than the first one. © 2010 Copyright SPIE - The International Society for Optical Engineering.

Pr doped Li-6 glass scintillator for Inertial Confinement Fusion neutron diagnostics Reviewed

Yasunobu Arikawa, Kouhei Yamanoi, Tomoharu Nakazato, Elmer Surat Estacio, Toshihiko Shimizu, Nobuhiko Sarukura, Mitsuo Nakai, Takayoshi Norimatsu, Youichirou Hironaka, Hiroshi Azechi, Takahiro Murata, Shigeru Fujino, Hideki Yoshida, Kei Kamada, Yoshiyuki Usuki, Toshihisa Suyama, Akira Yoshikawa, Nakahiro Sato, Hirofumi Kan

2010 CONFERENCE ON LASERS AND ELECTRO-OPTICS (CLEO) AND QUANTUM ELECTRONICS AND LASER SCIENCE CONFERENCE (QELS) 2010

Present status and future prospect of Fast Ignition Realization Experiment (FIREX) Project at ILE, Osaka Reviewed

H. Nishimura, H. Azechi, K. Mima, Y. Fujimoto, S. Fujioka, H. Homma, T. Jitsuno, T. Johzaki, M. Koga, J. Kawanaka, T. Kawasaki, N. Miyanaga, H. Murakami, M. Murakami, H. Nagatomo, N. Morio, K. Nagai, M. Nakai, T. Nakamura, T. Nakazato, Y. Nakata, K. Nishihara, T. Norimatsu, Y. Sakawa, N. Sarukura, K. Shigemori, T. Shimizu, H. Shiraga, K. Sueda, K. Tsubakimoto, A. Iwamoto, T. Mito, H. Sakagami, M. Isobe, T. Ozaki, O. Motojima, R. Kodama, K. A. Tanaka, H. Habara, K. Kondo, Y. Nakao, Y. Sentoku, A. Sunahara, T. Taguchi, T. Kanabe

2ND INTERNATIONAL CONFERENCE ON ULTRA-INTENSE LASER INTERACTION SCIENCE 1209 83 - + 2010

Thermonuclear ignition and subsequent burn are key physics for achieving laser fusion. In fast ignition, a highly compressed fusion fuel generated with multiple ns-laser beams is rapidly heated with a large energy, ps-laser pulse in prior to core disassembly. This scheme has a high potential to achieve ignition and burn since driver energy required for high fusion gain is predicted to be about one tenth of that needed for the central ignition scheme. In Japan, Fast Ignition Realization Experiment (FIREX) project has been started to clarify the physics of energy transport and deposition in the core plasma and to demonstrate fuel temperature of above 5 keV. After the success, FIREX-I will be followed by the second phase of the project (FIREX-II) to demonstrate ignition and burn. LFEX laser, designed to deliver a laser pulse of 10 kJ in 10 ps, are operational and the first phase of FIREX experiments has been stated. A new target is proposed to attain dense compression of fuel and improve laser-core coupling efficiency by adopting double-cone structure, a low-density inner liner, low-Z outer coating, and Br-doped fuel shell. In this paper, present status and near term prospects of the FIREX-I project will be reported together with activities on target designing, laser development, and plasma diagnostics.

Study on possible fuel layering sequence for FIREX target Reviewed

A. Iwamoto, T. Fujimura, M. Nakai, K. Nagai, T. Norimatsu, H. Azechi, R. Maekawa, H. Sakagami

SIXTH INTERNATIONAL CONFERENCE ON INERTIAL FUSION SCIENCES AND APPLICATIONS, PARTS 1-4 244 2010

A new procedure of fuel layering for the Fast Ignition Realization Experiment (FIREX) target is proposed. A conical laser guide heating technique was experimentally demonstrated in principle as the followings. It employed the target consisting of a polystyrene (PS) shell, a fill tube and a conical laser guide. At first, liquid fuel was fed into the shell and existed around the conical laser guide because the surface tension of the fuel must cause it. Then, it was solidified. The laser light provided a heat source to the conical laser guide so that the solid fuel was moved to the other interior of the shell. This process resulted in missing solid fuel around the conical laser guide. To fill the vacant space, liquid fuel was added as temperature was raised to the melting point. After the liquid fuel addition, temperature was lowered to the solidification point again. During this process, most of the solid fuel could survive.

Pr3+-doped fluoro-oxide lithium glass as scintillator for nuclear fusion diagnostics Reviewed

Yasunobu Arikawa, Kohei Yamanoi, Tomoharu Nakazato, Elmer Surat Estacio, Toshihiko Shimizu, Nobuhiko Sarukura, Mitsuo Nakai, Takayoshi Norimatsu, Hiroshi Azechi, Takahiro Murata, Shigeru Fujino, Hideki Yoshida, Kei Kamada, Yoshiyuki Usuki, Toshihisa Suyama, Akira Yoshikawa, Nakahiro Sato, Hirofumi Kan

REVIEW OF SCIENTIFIC INSTRUMENTS 80 ( 11 ) 2009.11

Experimental results are presented on the neutron scintillating properties of a custom-designed Pr3+(praseodymium)-doped lithium (Li) glass. Luminescence was observed at 278 nm wavelength, originating from the 5d-4f transition. Time-resolved measurements yielded about 20 ns decay times for ultraviolet and x-ray excitation while much faster decay times of about 6 ns were observed for alpha particle and neutron excitation. Actual time-of-flight data in laser fusion experiments at the GEKKO XII facility of the Institute of Laser Engineering, Osaka University reveal that it can clearly discriminate fusion neutrons from the much stronger x-rays signals. This material can promise improved accuracy in future scattered neutron diagnostics. (C) 2009 American Institute of Physics. [doi:10.1063/1.3254444]

Plasma physics and laser development for the Fast-Ignition Realization Experiment (FIREX) Project Reviewed

H. Azechi, K. Mima, Y. Fujimoto, S. Fujioka, H. Homma, M. Isobe, A. Iwamoto, T. Jitsuno, T. Johzaki, R. Kodama, M. Koga, K. Kondo, J. Kawanaka, T. Mito, N. Miyanaga, O. Motojima, M. Murakami, H. Nagatomo, K. Nagai, M. Nakai, H. Nakamura, T. Nakamura, T. Nakazato, Y. Nakao, K. Nishihara, H. Nishimura, T. Norimatsu, T. Ozaki, H. Sakagami, Y. Sakawa, N. Sarukura, K. Shigemori, T. Shimizu, H. Shiraga, A. Sunahara, T. Taguchi, K. A. Tanaka, K. Tsubakimoto

NUCLEAR FUSION 49 ( 10 ) 2009.10

Since the approval of the first phase of the Fast-Ignition Realization Experiment (FIREX-I), we have devoted our efforts to designing advanced targets and constructing a petawatt laser, which will be the most energetic petawatt laser in the world. Scientific and technological improvements are required to efficiently heat the core plasma. There are two methods that can be used to enhance the coupling efficiency of the heating laser to the thermal energy of the compressed core plasma: adding a low-Z foam layer to the inner surface of the cone and employing a double cone. The implosion performance can be improved in three ways: adding a low-Z plastic layer to the outer surface of the cone, using a Br-doped plastic ablator and evacuating the target centre. An advanced target for FIREX-I was introduced to suit these requirements. A new heating laser (LFEX) has been constructed that is capable of delivering an energy of 10 kJ in 10 ps with a 1 ps rise time. A fully integrated fast-ignition experiment is scheduled for 2009.

Fabrication of aerogel capsule, bromine-doped capsule, and modified gold cone in modified target for the Fast Ignition Realization Experiment (FIREX) Project Reviewed

Keiji Nagai, H. Yang, T. Norimatsu, H. Azechi, F. Belkada, Y. Fujimoto, T. Fujimura, K. Fujioka, S. Fujioka, H. Homma, F. Ito, A. Iwamoto, T. Jitsuno, Y. Kaneyasu, M. Nakai, N. Nemoto, H. Saika, T. Shimoyama, Y. Suzuki, K. Yamanaka, K. Mima

NUCLEAR FUSION 49 ( 9 ) 2009.9

The development of target fabrication for the Fast Ignition Realization EXperiment (FIREX) Project is described in this paper. For the first stage of the FIREX Project (FIREX-I), the previously designed target has been modified by using a bromine-doped ablator and coating the inner gold cone with a low-density material. A high-quality bromine-doped capsule without vacuoles was fabricated from bromine-doped deuterated polystyrene. The gold surface was coated with a low-density material by electrochemical plating. For the cryogenic fuel target, a brand new type of aerogel material, phloroglucinol/formaldehyde (PF), was investigated and encapsulated to meet the specifications of 500 mu m diameter and 20 mu m thickness, with 30 nm nanopores. Polystyrene-based low-density materials were investigated and the relationship between the crosslinker content and the nanopore structure was observed.

Developments of nuclear diagnostics for fast ignition experiments in laser fusion Reviewed

H. Nakamura, Y. Arikawa, H. Habara, M. Isobe, R. Kodama, M. Koga, M. Nakai, H. Nishimura, T. Ozaki, Y. Sakawa, N. Sarukura, H. Shiraga, Ka. Tanaka, H. Azechi

ABSTRACTS OF PAPERS OF THE AMERICAN CHEMICAL SOCIETY 238 2009.8

TEMPERATURE CONTROL IN A CRYOGENIC TARGET WITH A CONICAL LASER GUIDE FOR FUEL LAYERING Reviewed

A. Iwamoto, T. Fujimura, M. Nakai, T. Norimatsu, K. Nagai, R. Maekawa, H. Sakagami, T. Mito, O. Motojima, H. Azechi, K. Mima

FUSION SCIENCE AND TECHNOLOGY 56 ( 1 ) 427 - 431 2009.7

Fuel layering of a cryogenic target with a conical laser guide such as the FIREX target is complicated because of its non-spherical symmetry appearance. To simplify the layering, a foam layer is planned to utilize as a supporting material of fuel. Ideally, the foam shell has self-fuel-layering ability at a liquid state owing to the capillarity of the foam material. For stable fuel compression in laser experiments, the fuel must be solid with a lower saturated pressure. The transition to a solid state expects to cause random fuel crystallization and voids from the density difference between liquid and solid A volumetric heat load might help to finish fuel layering even in the foam shell. Solid fuel redistribution will ignore the foam boundary. Temperature control in the target, therefore, is required during the formation of a uniform layer. For the rough estimation of the target temperature, the possibility of the ANSYS code was confirmed compared with the experiment using a dummy target. Then, steady state temperature profiles of the FIREX target were calculated using the ANSYS code. Temperature control to practically realize a uniform solid fuel layer in the FIREX target is discussed.

Experimental Evidence of Impact Ignition: 100-Fold Increase of Neutron Yield by Impactor Collision Reviewed

H. Azechi, T. Sakaiya, T. Watari, M. Karasik, H. Saito, K. Ohtani, K. Takeda, H. Hosoda, H. Shiraga, M. Nakai, K. Shigemori, S. Fujioka, M. Murakami, H. Nagatomo, T. Johzaki, J. Gardner, D. G. Colombant, J. W. Bates, A. L. Velikovich, Y. Aglitskiy, J. Weaver, S. Obenschain, S. Eliezer, R. Kodama, T. Norimatsu, H. Fujita, K. Mima, H. Kan

PHYSICAL REVIEW LETTERS 102 ( 23 ) 2009.6

We performed integrated experiments on impact ignition, in which a portion of a deuterated polystyrene (CD) shell was accelerated to about 600 km/s and was collided with precompressed CD fuel. The kinetic energy of the impactor was efficiently converted into thermal energy generating a temperature of about 1.6 keV. We achieved a two-order-of-magnitude increase in the neutron yield by optimizing the timing of the impact collision, demonstrating the high potential of impact ignition for fusion energy production.

Shock Hugoniot and temperature data for polystyrene obtained with quartz standard Reviewed

N. Ozaki, T. Sano, M. Ikoma, K. Shigemori, T. Kimura, K. Miyanishi, T. Vinci, F. H. Ree, H. Azechi, T. Endo, Y. Hironaka, Y. Hori, A. Iwamoto, T. Kadono, H. Nagatomo, M. Nakai, T. Norimatsu, T. Okuchi, K. Otani, T. Sakaiya, K. Shimizu, A. Shiroshita, A. Sunahara, H. Takahashi, R. Kodama

PHYSICS OF PLASMAS 16 ( 6 ) 2009.6

Equation-of-state data, not only pressure and density but also temperature, for polystyrene (CH) are obtained up to 510 GPa. The region investigated in this work corresponds to an intermediate region, bridging a large gap between available gas-gun data below 60 GPa and laser shock data above 500 GPa. The Hugoniot parameters and shock temperature were simultaneously determined by using optical velocimeters and pyrometers as the diagnostic tools and the alpha-quartz as a new standard material. The CH Hugoniot obtained tends to become stiffer than a semiempirical chemical theoretical model predictions at ultrahigh pressures but is consistent with other models and available experimental data.

SMOOTH MEMBRANE FORMATION ON RESORCINOL-FORMALDEHYDE AEROGEL BALLS GELATED USING A BASIC PHASE-TRANSFER CATALYST Reviewed

Fuyumi Ito, Naotake Nakamura, Keiji Nagai, Mitsuo Nakai, Takayoshi Norimatsu

FUSION SCIENCE AND TECHNOLOGY 55 ( 4 ) 465 - 471 2009.5

Low-density foam balls with a diameter of similar to 1 mm were produced from a density-matched emulsion consisting of a resorcinol-formaldehyde (RF) aqueous solution (W) and an exterior oil of carbontetrachloride/(mineral oil) (O). Phase-transfer catalysts such as an alkyl amine were dissolved in the exterior oil, following which the catalyst moved into the RF solution from the exterior oil. A gelation process was monitored by a complete gelation test. When the basic catalysts were used at room temperature as a phase-transfer catalyst, gelation occurred within 30 to 120 min, whereas when the acidic catalyst was used, gelation occurred within 20 to 30 min at room temperature. When similar to 0.39 wt% of triethylamine and tri(n-butyl)amine in the oil phase were based, complete gelation took place. A basic catalyst with a long alkyl chain such as dimethyl(n-hexyl)amine did not induce gelation. The gelated balls obtained using the basic catalyst with a short alkyl chain were dried by extraction using super-critical fluid CO2 and the solvent was replaced with 2-propanol to produce the foam structure. Except 0.39 wt% tri(n-butyl)amine, the basic catalysts yielded foam balls with higher densities of 173 to 184 mg/cm(3) as compared to those obtained from a benzoic acid catalyst, namely, 158 mg/cm(3). The density difference can be attributed to the inclusion of the basic catalyst in the RF solution. Scanning electron microscopy images revealed a surface membrane formation, which can be explained by local concentration at the W/O interface. The cell size of the bulk foam was observed to depend on the catalysts, and it was surmised that the cell sizes varied because of the different gelation rates. A smooth surface membrane tri(n-butyl)amine was used as a catalyst. The membrane obtained on using a basic phase-transfer catalyst was smoother than that obtained on using an acid catalyst. Such a smooth membrane is useful for coating the ablation layer of foam capsule targets.

Manufacturing of leak check of shell targets for FIREX-I project Reviewed

Takeshi Fujimura, Mitsuo Nakai, Akifumi Iwamoto, Keiji Nagai, Hirofumi Homma, Ken-ichi Tanabe, Takayoshi Norimatsu

Plasma and Fusion Research 4 ( S1010 ) S1010 - S1010 2009.4

This article reports the latest progress in the manufacture of shell targets used for the first stage of the Fast Ignition Realization Experiment (FIREX-I). In the project, the targets are cooled to cryogenic temperature and filled with hydrogen isotope fuel through a gas feed tube. If the target has a leak or the gas feeder is blocked, the experiments cannot be carried out successfully and waste much time. The authors have developed a system to check integrity of the targets. SF6 is used instead of H2 or D2 because of its high refractive index and low diffusivity. When SF6 is loaded into the target, the optical path length that passes through a target is longer than that of an evacuated target. The difference can be measured with an interferometer. Analyzing the interference images, it is possible to know whether the gas feeder is blocked and a leak is present. The validity of the system was experimentally confirmed.

Advanced target design for the FIREX-I project Reviewed

Hiroshi AZECHI, Mitsuo NAKAI, Hirofumi HOMMA, Tomoyuki JOHZAKI, Mayuko KOGA, Kunioki MIMA, Noriaki MIYANAGA, Masakatsu MURAKAMI, Hideo NAGATOMO, Keiji NAGAI, Tatsufumi NAKAMURA, Katsunobu NISHIHARA, Hiroaki NISHIMURA, Takayoshi NORIMATSU, Youichi SAKAWA, Keisuke SHIGEMORI, Hiroyuki SHIRAGA, Akifumi IWAMOTO, Toshiyuki MITO, Hitoshi SAKAGAMI, Osamu MOTOJIMA, Ryosuke KODAMA, Kazuo A. TANAKA, Atsushi SUNAHARA

Plasma Fusion Res. 4 ( S1001 ) S1001 - S1001 2009.4

Cryogenically cooled foam shells with deuterium and tritium fuels are expected to be utilized in the fast ignition realization experiment project of ILE, Osaka University, to demonstrate efficient heating of properly compressed fuel plasmas. These targets consist of a foam shell with solid fuel and a conical light guide for additional heating with an ultra-high intensity laser beam, in accordance with previous preliminary experiments [R. Kodama et al., Nature 412, 798 (2001).] Recent theoretical predictions and elemental experiments have suggested some advanced modifications to enhance the coupling efficiency of fast heating and improve implosion performance. The five major points of these improvements are as follows: 1) use of a low-Z foam layer on the inner surface of the cone; 2) use of a double-layered cone as a light guide; 3) use of a low-Z plastic layer on the outer surface of the cone; 4) adding a Br-doped plastic ablator to the fuel capsule; and 5) evacuation of the target center.

Proposal on Temperature Control Procedure of the Cryogenic Target for the FIREX Project Reviewed

Akifumi Iwamoto, Takeshi Fujimura, Mitsuo Nakai, Takayoshi Norimatsu, Keiji Nagai, Ryuji Maekawa, Hitoshi Sakagami

Plasma and Fusion Research 4 ( S1007 ) S1007 - S1007 2009.4

One of the techniques to produce a uniform solid fuel layer for the Fast Ignition Realization EXperiment (FIREX) target is applying a solid fuel redistribution process. During the redistribution process, temperature control is essential for the FIREX target, because a cone guide, also called a conical laser guide, causes temperature non-uniformity. To minimize its temperature distribution, one possible procedure is temperature control at the cone guide. A radiation plate for indirect temperature control, installed next to the cone guide, is proposed. As the heat input to the radiation plate was varied, the temperature profile of the target was calculated using the ANSYS code. The optimal heat input was evaluated. The feasibility of using a radiation plate is discussed.

Ultrathin amorphization of single-crystal silicon by ultraviolet femtosecond laser pulse irradiation Reviewed

Izawa Yusaku, Tokita Shigeki, Fujita Masayuki, Nakai Mitsuo, Norimatsu Takayoshi, Izawa Yasukazu

JOURNAL OF APPLIED PHYSICS 105 ( 6 ) 2009.3

Streaked x-ray backlighting with twin-slit imager for study of density profile and trajectory of low-density foam target filled with deuterium liquid Reviewed

H. Shiraga, N. Mahigashi, T. Yamada, S. Fujioka, T. Sakaiya, K. Shigemori, M. Nakai, H. Azechi, A. Sunahara

REVIEW OF SCIENTIFIC INSTRUMENTS 79 ( 10 ) 2008.10

Low-density plastic foam filled with liquid deuterium is one of the candidates for inertial fusion target. Density profile and trajectory of 527 nm laser-irradiated planer foam-deuterium target in the acceleration phase were observed with streaked side-on x-ray backlighting. An x-ray imager employing twin slits coupled to an x-ray streak camera was used to simultaneously observe three images of the target: self-emission from the target, x-ray backlighter profile, and the backlit target. The experimentally obtained density profile and trajectory were in good agreement with predictions by one-dimensional hydrodynamic simulation code ILESTA-1D. (C) 2008 American Institute of Physics. [DOI: 10.1063/1.2966458]

Rayleigh-Taylor instability growth on low-density foam targets Reviewed

T. Watari, M. Nakai, H. Azechi, T. Sakaiya, H. Shiraga, K. Shigemori, S. Fujioka, K. Otani, K. Nagai, A. Sunahara, H. Nagatomo, K. Mima

PHYSICS OF PLASMAS 15 ( 9 ) 2008.9

In recent laser fusion programs, foam cryogenic targets have been developed as promising targets which have a great potential to realize efficient nuclear fusion. The foam is porous plastic material having a microstructure inside. We observed the growth of the Rayleigh-Taylor (RT) instability on the foam target with initial surface perturbation for the first time. The measured RT growth rate on the foam target was clearly suppressed in comparison to that of normal-density polystyrene (CH) targets. The values of the RT growth rate for the low-density foam target and the normal-density CH target were 0.84 +/- 0.15 (1/ns) and 1.33 +/- 0.1 (1/ns), respectively. (c) 2008 American Institute of Physics.

Development of TOF Neutron Spectrometer for the measurement of degenerated plasma in Fast Ignition experiment Reviewed

H. Hosoda, M. Nakai, H. Furukawa, T. Watari, H. Azechi, N. Izumi, Y. Arikawa, Y. Sakawa, S. Dono, T. Fujiwara, K. Mima

5TH INTERNATIONAL CONFERENCE ON INERTIAL FUSION SCIENCES AND APPLICATIONS (IFSA2007) 112 2008

There are two essential requirements to achieve the Fast Ignition. One is high density compression of main fuel and the other one is additional heating of main fuel by ultra intense laser. Then the experimental determination of both the density of the main fuel before heating laser irradiation and ion temperature after heating laser irradiation is necessary. In the experiment of the Central Ignition, we developed both ion temperature measurement and density measurement, which is based on theoretical degenerated plasma model, by using Time-Of-Flight neutron spectrometer. The main problem in applying this measurement in Fast Ignition experiment is huge amount of high energy x ray, which is generated as a result of heating laser irradiation. Then we installed a total 15-cm thick lead shield as a measure against it. It was confirmed that the newly installed shield achieves x ray attenuation to 5.7 +/- 2.0x10(-4) of previous level by Geant4 MC simulation. And the error for ion temperature measurement was confirmed to be smaller than 0.3 keV in an experiment whose neutron yield was 1.7 +/- 0.2x10(6).

Developments of characterization of the foam shell target for Fast Ignition Realization Experiment-I (FIREX-I) Reviewed

Fujimura, T, Iwamoto, A, Nakai, M, Norimatsu, T, Nagai, K, Yang, H, Kimura, Y, Sakagami, H, Mito, T, Mima, K

5TH INTERNATIONAL CONFERENCE ON INERTIAL FUSION SCIENCES AND APPLICATIONS (IFSA2007) 112 32066 2008

Experimental Investigation of Aerosol Formation in Laser Fusion Reactor Chamber by Discharge Method Reviewed

T. Ohshige, T. Norimatsu, H. Furukawa, M. Nakai, K. Nagai, K. Mima

5TH INTERNATIONAL CONFERENCE ON INERTIAL FUSION SCIENCES AND APPLICATIONS (IFSA2007) 112 2008

Fast response neutron scintillation detector for FIRE-X Reviewed

Y. Arikawa, M. Nakai, T. Watari, H. Hosoda, K. Takeda, T. Fujiwara, Y. Furukawa, T. Norimatsu, H. Shiraga, N. Sarukura, H. Azechi

5TH INTERNATIONAL CONFERENCE ON INERTIAL FUSION SCIENCES AND APPLICATIONS (IFSA2007) 112 2008

We have been developing fast responding neutron detectors with a view to revealing the effect of additional laser heating in FIREX-I (Fast Ignition Realization Experiment) by measuring the burn time with a time resolution under 100 ps at the relatively low neutron yield (about10(6)). The detector is constructed with a thin plastic-scintillaotor (BC-422), a micro-channel-plate photomultiplier tube (MCP-PMT) and a bundle optical fiber as a light-guide. The rise time of a neutron signal from the detector is measured to be 220 ps. The time-determination error for measuring burn time is estimated to be less the +/- 46 ps from the data of characterization experiments measuring the transit time distribution of signals, and calculated values of Doppler broadening and the uncertainty of the scintillation time due to the thickness of the scintillator. In the future with more neutron yield, we will construct a scintillatiion-fiber-streak camera to detect burn history.

Fabrication and Characterization of Planar Cryogenic Targets for GEKKO-XII Reviewed

T. X. Huang, M. Nakai, K. Shigemori, H. Shiraga, T. Sakaiya, T. Watari, K. Ohtani, T. Shiota, K. Takeda, O. Maegawa, H. Azechi, M. Nagata, T. Norimatsu, K. Nagai, K. Mima, Y. Izawa, T. Mito, K. Iwamoto

5TH INTERNATIONAL CONFERENCE ON INERTIAL FUSION SCIENCES AND APPLICATIONS (IFSA2007) 112 2008

A planar cryogenic target system was built to simulate the ablator+fuel shell physics in ICF experimental studies. In the center of the target cell, a sandwich target of liquid deuterium was formed, which has open geometry for conventional side-on and face-on backlighting diagnostics. A set of double-flanges comprised a sealing flange and an extra flange, with which the target thickness could be changed using proper spacers. Furthermore, an interferometric method was used to characterize the cryogenic target before laser shot. The in situ target thickness and bulging shape could be obtained with acceptable accuracy. A typical planar cryogenic target was formed with diameter of 2 mm, which comprised three parts: a 7-m thick polyimide film, a layer of liquid deuterium with the thickness of 119 mu m at the center and 100 mu m at the edge, and another 7-mu m thick polyimide film.

Neutron generation from Impact Fast Ignition Reviewed

T. Watari, T. Sakaiya, H. Azechi, M. Nakai, H. Shiraga, K. Shigemori, H. Hosoda, H. Saito, Y. Arikawa, Y. Sakawa, S. Fujioka, Y. Hironaka, M. Murakami, M. Karasik, J. Gardner, J. Bates, D. Colombant, J. Weber, S. Obenschain, Y. Aglitsky, P. A. Norreys, S. Eliezer, K. Mima

5TH INTERNATIONAL CONFERENCE ON INERTIAL FUSION SCIENCES AND APPLICATIONS (IFSA2007) 112 2008

We have proposed a new ignition scheme of Fast Ignition, called "Impact Fast Ignition [1] (IFI)", in which a compressed fuel is ignited by impact collision of a fragment of separately imploded fuel. We have started experiments that used CD colliding foils as the fundamental experiment and integrated experiment of the IFI. In the fundamental experiment, we used targets which are consists of two CD foils (thickness of 20 m) with a 600 m separation. We have irradiated one of the CD foils by laser beams of the energy of 2 kJ in total and accelerated. The accelerated CD foil collides with another foil, and neutrons were generated by the nuclear fusion reaction on the heated foil. In this experiment, we measured the neutron yield of 10(6). In the integrated experiment, we used CD shell targets with a gold cone which had a hemispherical impactor (Fig. 1). The shell was imploded using 9 beams and the impactor was accelerated using 3 beams of the GEKKO XII laser system. The laser energy was 350 J per beam. Observed maximum neutron yield was 2x10(6). This yield was 80 times as large as that without impactor. We will present the experimental details and results.

Application of bubble detector in FIREX program Reviewed

Osamu Maegawa, Takashi Fujiwara, Mitsuo Nakai, Hiroyuki Shiraga

5TH INTERNATIONAL CONFERENCE ON INERTIAL FUSION SCIENCES AND APPLICATIONS (IFSA2007) 112 2008

In a Fast Ignition Realization Experiment (FIREX), measurement of the primary and the secondary neutron yield is one of the key diagnostics. However, gamma-ray background generated by an ultra-short pulse laser irradiation makes it difficult to measure the neutron yield in the fast ignition experiment. We adopted a bubble neutron detector as a promising gamma-insensitive detector to be developed and started to examine the feasibility of the detector using commercially available dosimeters provided from BTI inc. [1].

Solution viscosity adjustable phloroglucinolcarboxylic acid / formaldehyde applied in extremely thin shell fusion target fabrication Reviewed

H. Yang, K. Nagai, M. Nakai, T. Norimatsu

5TH INTERNATIONAL CONFERENCE ON INERTIAL FUSION SCIENCES AND APPLICATIONS (IFSA2007) 112 2008

Capsuliform fusion target was prepared by using the O(O) / W / O(I) emulsion process. Phloroglucinolcarboxylic acid / formaldehyde (PF) is expected to be used as the water phase (W) solution which then gelates to be the shell of the capsule. The density of the shell should be low to obtain high laser gain. Phloroglucinolcarboxylic acid had addition and condensation reaction with formaldehyde under basic condition to form linear polymer first. The nano-scale linear polymers were then linked via noncovalent interactions, such as hydrogen bonding, van der Waals, to continue the gelation process. The type and amount of the base catalyst used in the reaction can affect the polymerization of PF, including the gelation rate and gelation concentration. By changing the basic condition of the reaction, the proper viscosity of 9x10(-5) for capsuliform target fabrication was reached and extremely thin gel shell thickness of 17 mu m with low polymer concentration of 26.3mg/cm(3) was obtained.

Temperature Measurement of Preheated Planar-Cryogenic Targets Reviewed

K. Otani, K. Shigemori, D. Ichinose, T. Sakaiya, A. Sunahara, Y. Sakawa, M. Nakai, H. Shiraga, H. Azechi, K. Mima

5TH INTERNATIONAL CONFERENCE ON INERTIAL FUSION SCIENCES AND APPLICATIONS (IFSA2007) 112 2008

The temperature measurement of preheated target is reported. Inertial confinement fusion (ICF) targets should be imploded with a low adiabat for achievement of high density compression. The high energy photons and electrons from ablation plasma can preheat the uncompressed fuel and disturb the low adiabat compression. Preheat has to be evaluated and suppressed for ICF targets. The planar target of cryogenic deuterium was developed for measurement of the self emission from the rear surface. Experiment indicated that the x-ray preheating is more effective than that of non-local electron heat transport at the laser intensity of 10(14) W/cm(2).

Study on a fuel layering sequence of the foam target for the FIREX project Reviewed

Iwamoto, A, Fujimura, T, Nakai, M, Nagai, K, Norimatsu, T, Maekawa, R, Mito, T, Sakagami, H, Motojima, O, Azechi, H, Mima, K

5TH INTERNATIONAL CONFERENCE ON INERTIAL FUSION SCIENCES AND APPLICATIONS (IFSA2007) 112 32067 2008

Reduction of the Rayleigh-Taylor instability growth with cocktail color irradiation Reviewed

K. Otani, K. Shigemori, T. Sakaiya, S. Fujioka, A. Sunahara, M. Nakai, H. Shiraga, H. Azechi, K. Mima

PHYSICS OF PLASMAS 14 ( 12 ) 2007.12

A novel method for reducing the Rayleigh-Taylor instability (RTI) growth in inertial confinement fusion (ICF) targets is reported. It is well known that high-density compression of ICF targets is potentially prevented by the RTI. Previous studies [K. Shigemori , Phys. Rev. Lett. 78, 250 (1997), S. G. Glendinning , Phys. Rev. Lett. 78, 3318 (1997), and H. Azechi , Phys. Plasmas 4, 4079 (1997)] have indicated that nonlocal electron heat transport enhances the effect on the ablative stabilization of the RTI growth with long wavelength laser irradiation. Planar target experiments, using a small fraction of a long wavelength laser (lambda=0.53 or 1.05 mu m) in addition to the main drive laser (lambda=0.35 mu m), were conducted to verify the RTI reduction by inducing the effect of the nonlocal electron heat transport. The measured RTI growth rate for this "cocktail-color" laser irradiation was clearly reduced from that for the "single-color" short-wavelength laser irradiation. The experimental growth factors are in good agreement with the ablative RTI formula coupled with a one-dimensional Fokker-Planck simulation code. (c) 2007 American Institute of Physics.

Recent results and future prospects of laser fusion research at ILE, Osaka Reviewed

K. Mima, K. A. Tanaka, R. Kodama, T. Johzaki, H. Nagatomo, H. Shiraga, N. Miyanaga, M. Murakami, H. Azechi, M. Nakai, T. Norimatu, K. Nagai, T. Taguchi, H. Sakagami

EUROPEAN PHYSICAL JOURNAL D 44 ( 2 ) 259 - 264 2007.8

Reviewed are the present status of the fast ignition researches. Since 1997, the fast ignition experiment and theory researches have been extensively continued at the Institute of Laser Engineering of Osaka University. In particular, the cone-shell target experiments and simulation research have been progressing. In order to demonstrate heating of imploded high density plasma to the ignition temperature, in the April of 2003, the construction of heating laser of 10 kJ/10 ps/1.06 mu m (Laser for Fusion Experiment; LFEX), for FIREX-I (Fast Ignition Realization Experiment) has started. The fabrication of DT foam cryogenic cone target is also under development as a collaboration program between Osaka University and NIFS (National Institute for Fusion Science). The LFEX will be completed in 2008. After the completion of LFEX, the foam cryogenic cone shell target experiment will start in 2008. As a new approach toward a compact ignition, an impact fusion has been proposed, where the ablative acceleration to the order of 10(8) cm/s is the key issue. The ablation acceleration related to the impact fusion has been explored by experiments.

Foam structure of xerogel prepared via ring-opening reaction between epoxy groups attached on the side chain of polystyrene Reviewed

Kentaro Yamanaka, Keiji Nagai, Nobukatsu Nemoto, Kaori Nomura, Tomonori Shimoyama, Kei Tanji, Tomoya Tanji, Mitsuo Nakai, Takayoshi Norimatsu

FUSION SCIENCE AND TECHNOLOGY 51 ( 4 ) 665 - 672 2007.5

This paper deals with a new foam material containig polysytrene and its oxirane derivative. A monomer, 4-vinylphenyloxirane (MI), was prepared from 4-chlorostyrene. Polystyrene-based copolymers using styrene and M1 were prepared by free radical copolymerization using azo-bis(isobutyronitrile) (AIBN) as an initiator. The solutions of the obtainedpolystyrene-based copolymers in 4-chlorotoluene were gelated by the addition of a cationic initiator, which caused crosslinking via ring-opening polymerization of the pendant cyclic moieties. SEM images of the dried gel show various foam structures. The formation mechanism of the micro- and nano-structure was explained from the view point of the affinity of the monomer unit and the solvent. The homopolymer of 4-vinyphenylolxirane showed the finest and most uniform structure.

Laser machining of RF foam by second harmonics of Nd : Yag laser Reviewed

Takeshi Fujimura, Takayoshi Norimatsu, Mitsuo Nakai, Keiji Nagai, Akifumi Iwamoto, Kunioki Mima

FUSION SCIENCE AND TECHNOLOGY 51 ( 4 ) 677 - 681 2007.5

A way to make a hole in a resorcinol-formaldehyde (RF) foam shell target is described. A target used in fast ignition (FI) experiments consists of an RF foam shell and a guide cone. The fragile RF foam cannot accept conventional mechanical drilling or laser machining. We used the second harmonics of a Nd:YAG laser (532nm) to bore a hole for the cone by utilizing thermal decomposition of the RF foam.
To optimize the cutting condition, the thermal characteristic and absorption spectrum of the RF foam were measured with a thermo-gravimetric meter and a spectrometer respectively. Then, using these results, relationships between the laser power and cutting speed were optimized for RF foams with several densities.

Preliminary results of fuel layering on the cryogenic target for the firex project Reviewed

Iwamoto, A, Maekawa, R, Mito, T, Sakagami, H, Motojima, O, Nakai, M, Nagai, K, Fujimura, T, Norimatsu, T, Azechi, H, Mitna, K

FUSION SCIENCE AND TECHNOLOGY 51 ( 4 ) 753 - 757 2007.5

Comprehensive diagnosis of growth rates of the ablative Rayleigh-Taylor instability Reviewed

H. Azechi, T. Sakaiya, S. Fujioka, Y. Tamari, K. Otani, K. Shigemori, M. Nakai, H. Shiraga, N. Miyanaga, K. Mima

PHYSICAL REVIEW LETTERS 98 ( 4 ) 2007.1

The growth rate of the ablative Rayleigh-Taylor instability is approximated by gamma=root kg/(1+kL)-beta km/rho(a), where k is the perturbation wave number, g the gravity, L the density scale length, m the mass ablation rate, and rho(a) the peak target density. The coefficient beta was evaluated for the first time by measuring all quantities of this formula except for L, which was taken from the simulation. Although the experimental value of beta=1.2 +/- 0.7 at short perturbation wavelengths is in reasonably good agreement with the theoretical prediction of beta=1.7, it is found to be larger than the prediction at long wavelengths.

Encapsulation of low density materials for the first stage of fast ignition realization experiment (FIREX-I) - Control of microstructure and gelation process using a phase-transfer catalyst and tailored polymers Reviewed

Keiji Nagai, F. Ito, H. Yang, A. Iwamoto, M. Nakai, H. Homma, H. Shiraga, H. Azechi, K. A. Tanaka, R. Kodama, T. Norimatsu, K. Mima

22ND IEEE/NPSS SYMPOSIUM ON FUSION ENGINEERING 33 - + 2007

Development of foam capsule fabrication for cryogenically cooled fuel targets is overviewed in the present paper. The fabrication development was initiated as a part of the Fast Ignition Realization Experiment (FIREX) Project at the ILE, Osaka University in the way of bilateral collaboration between Osaka University and National Institute for Fusion Science (NIFS). For the first stage of FIREX (FIREX-1), a foam cryogenic target was designed where low-density foam shells with a conical fight guide will be cooled down to the cryogenic temperature and will be fueled through a narrow pipe. The required diameter and thickness of the capsule are 500 pm and 20 [km, respectively. The material should be low-density plastics foam. We have prepared such capsules using 1) new material of (phloroglucinolcarboxylic acid)/formalin resin to control kinematic viscosity of the precursor, 2) phase-transfer-catalyzed gelation process to keep density matching of three phases of the emulsion. 3) non-volatile silicone oil as outer oil of emulsion in order to prevent hazard halogenated hydrocarbon and flammable mineral oil. The obtained foam capsule had fine structure of 180 nm (outer surface) to 220 nm (inner surface) and uniform thickness reaching to resolution limit of optical analysis (similar to 0.5 mu m). A small hole was made before the solvent exchange and the drying process to prevent distortion due to volume changes. The density of dried foam was 0.29 g/cm(3). After attaching the petawatt laser guiding cone and fueling glass tube, poly([2,2]paracyclophane) was coated on the foam surface and supplied for a fueling test of cryogenic hydrogen.

Progress of impact fast ignition

M. Murakami, H. Nagatomo, T. Sakaiya, S. Fujioka, H. Saito, H. Shiraga, M. Nakai, K. Shigemori, H. Azechi, M. Karasik, J. Gardner, J. Bates, D. Colombant, J. Weaver, A. Schmitt, A. Velikovich, Y. Aglitskiy, J. Sethian, S. Obenshain

34th EPS Conference on Plasma Physics 2007, EPS 2007 - Europhysics Conference Abstracts 31 ( 1 ) 21 - 24 2007

Fabrication of low-density solid xenon as laser-produced plasma extreme ultraviolet source Reviewed

Mizuho Nagata, Takayoshi Norimatsu, Mitsuo Nakai, Keiji Nagai, Nobuyoshi Ueda, Shinsuke Fujioka, Tatsuya Aota, Hiroaki Nishimura, Katsunobu Nishihara, Noriaki Miyanaga, Yasukazu Izawa, Kunioki Mima

JAPANESE JOURNAL OF APPLIED PHYSICS PART 2-LETTERS & EXPRESS LETTERS 45 ( 33-36 ) L884 - L886 2006.9

A low-density solid xenon (Xe) target has been developed as laser-produced plasma (LPP) extreme ultraviolet (EUV) source. Xe gas was cooled to below the condensation temperature, and liquid Xe was sprayed from a swirl atomizer into a low-pressure atmosphere. Microparticles of liquid Xe were rapidly cooled by their own latent heat of evaporation, and became a solid micrometer-sized powder. The most frequent particle diameter under an atomizing pressure of 0.3 MPa was 114 mu m, and the apparent density was 0.2 g/cm(3) 1/13 of the density of conventional solid Xe. The apparent production rate of the powder was 2.2 cm(3)/s.

Extreme ultraviolet emission from laser-irradiated low-density Xe targets Reviewed

Nobuyoshi Ueda, Mizuho Nagata, Hiroaki Nishimura, Shinsuke Fujioka, Tatsuya Aota, Yuzuri Yasuda, Yuichi Inubushi, Tsuyoshi Ando, Takayoshi Norimatsu, Mitsuo Nakai, Keiji Nagai, Katsunobu Nishihara, Atsushi Sunahara, Noriaki Miyanaga, Yasukazu Izawa, Kunioki Mima

JAPANESE JOURNAL OF APPLIED PHYSICS PART 1-REGULAR PAPERS BRIEF COMMUNICATIONS & REVIEW PAPERS 45 ( 7 ) 5951 - 5953 2006.7

The effect of the initial density of xenon (Xe) targets on extreme ultraviolet (EUV) emission has been investigated. With decreasing initial density, it was found that the spectral width around 11 nm becomes broad, and the intensity of 13.5 nm emission increases. The maximum conversion efficiency (CE) for solid Xe targets is approximately 0.6% at a 2 x 10(11) W/cm(2) of laser intensity, whereas that for the low-density targets is approximately 0.7% at a 4 x 10(11) W/cm(2). The spectral broadening with decreasing initial density can be attributed to the change in optical thickness of laser-produced plasmas. The enhancement of CE is attributed to optically thick plasma formation.

Conceptual design of laser fusion reactor KOYO-fast - Target design and the fueling system Reviewed

T. Norimatsu, T. Johzaki, H. Azechi, K. Mima, Y. Nakao, H. Sakagami, H. Shiraga, R. Kodama, H. Nagatomo, T. Endo, A. Iwamoto, H. Yoshida, M. Nakai

JOURNAL DE PHYSIQUE IV 133 841 - 843 2006.6

Preliminary results on the cryogenic target for FIREX project Reviewed

A. Iwamoto, R. Maekawa, T. Mito, M. Okamoto, O. Motojima, M. Nakai, T. Norimatsu, K. Nagai

JOURNAL DE PHYSIQUE IV 133 899 - 901 2006.6

Preliminary tests on the cryogenic target for the fast ignition realization experiment (FIREX) project has been conducted. A foam shell method is proposed to realize its target design. A foam target consists of three parts: a foam shell, a conical laser guide and a liquid or gas feeder made of glass. The shell is a hollow sphere (500 pm in diameter) with a uniform and thin foam layer (similar to 20 mu m in thickness). Epoxy resin is utilized to assemble the parts into the target. Regarding target fabrication, one of the concerns is the influence on various thermal contractions from the different materials when it is cooled down to cryogenic environment. This paper describes the result on the validity check at cryogenic environment and the demonstration of H-2 liquefaction using a dummy target instead of the foam target.

Recent results and future prospects of laser fusion research at ILE, Osaka Reviewed

K. Mima, K. A. Tanaka, R. Kodama, T. Johzaki, H. Nagatomo, H. Shiraga, N. Miyanaga, M. Murakami, H. Azechi, M. Nakai, T. Norimatsu, K. Nagai, T. Taguchi, H. Sakagami

JOURNAL DE PHYSIQUE IV 133 27 - 28 2006.6

Electrochemical fabrication of low density metal foam with mono-dispersed-sized micro- and submicro-meter pore Reviewed

K Nagai, D Wada, M Nakai, T Norimatsu

FUSION SCIENCE AND TECHNOLOGY 49 ( 4 ) 686 - 690 2006.5

This paper deals with the fabrication of low-density metal using micro-template and electrochemical plating techniques. Tin and gold foam films were demonstrated For both cases, porous foam plating required 0.5 V negatively higher bias potential than that for conventional metal plating. The electric current density values for them are smaller than those for bulk metal plating. In spite of these differences, the coulomb efficiency was almost the same as those for bulk metal plating. The density was almost close to the rest of closed packing density; 23 % of bulk metal for gold and 20 % of bulk metal for tin. These low-density foams will be applied for extreme ultraviolet (EUV) generation or other application through laser produced plasma.

Hugoniot measurement of diamond under laser shock compression up to 2 TPa Reviewed

H Nagao, KG Nakamura, K Kondo, N Ozaki, K Takamatsu, T Ono, T Shiota, D Ichinose, KA Tanaka, K Wakabayashi, K Okada, M Yoshida, M Nakai, K Nagai, K Shigemori, T Sakaiya, K Otani

PHYSICS OF PLASMAS 13 ( 5 ) 2006.5

Hugoniot data of diamond was obtained using laser-driven shock waves in the terapascal range of 0.5-2 TPa. Strong shock waves were generated by direct irradiation of a 2.5 ns laser pulse on an Al driver plate. The shock wave velocities in diamond and Al were determined from optical measurements. Particle velocities and pressures were obtained using an impedance matching method and known Al Hugoniot. The obtained Hugoniot data of diamond does not show a marked difference from the extrapolations of the Pavlovskii Hugoniot data in the TPa range within experimental errors. (c) 2006 American Institute of Physics.

Optimization of gelation to prepare hollow foam shell of resorcinol-formalin using a prase-transfer catalyst Reviewed

F Ito, K Nagai, M Nakai, T Norimatsu

FUSION SCIENCE AND TECHNOLOGY 49 ( 4 ) 663 - 668 2006.5

We studied the gelation of an RF foam shell using a phase-transfer catalyst and density-match non-volatile silicon oil. A phase-transfe catalyst circumvent the problem of density-mismatch and achieve gelation at room temperature, by which the catalyst is contained in the outer oil (O-o,) phase, and is then gradually transferred into the RF droplets. For the O-o phase, we used non-volatile silicon oil as a non-hazardous material instead of a toxic (mineral oil)/carbontetrachloride.
Vigorous agitation conditions were optimized based on three experiments. An emulsion was produced using a droplet generator, and was injected into a drum containg a mixture of 0.39% acetic acid and silicon oil. The drum was rotated and its speed were increased to 95 rpm within 15 minutes. Five minutes later, the rotation speed was increased to 120 rpm (maximum rotation speed), which was maintained for 1 minute, there after reduced to 95 rpm for 39 minutes.

Polystyrene based foam materials for cryogenic targets of fast ignition realization experiment (FIREX) Reviewed

N Nemoto, K Nagai, Y Ono, K Tanji, T Tanji, M Nakai, T Norimatsu

FUSION SCIENCE AND TECHNOLOGY 49 ( 4 ) 695 - 700 2006.5

This paper deals with the development of materials without volume change in the formation of uniform low density foam capsules with fine structures. Two monomers, i.e., 5-(4-vinylbenzyl)oxymethyl-5-methyl-1,3dioxane-2-thione (M1) and 4-vinylphenyloxirane (M2), were prepared as the comonomers polymerized with styrene. Polystyrene-based copolymers using styrene and M1 or M2 were prepared by free radical copolymerization using azobis(isoburyronitrile) (AIBN) as an initiator. The solutions of the obtained polystyrene-based copolymers in benzenel/dichloromethane mixture or 4-chlorotoluene were gelated by the addition of a cationic initiator, which caused cross-linking via ring-opening polymerization of the pendant cyclic moieties. The gel was transformed into an aerogel by exchanging solvent to 2-propanol, and removal of 2-propanol using supercritical CO2. SEM images of a cross sectional view of the aerogel indicated that sub-micrometer voids were distributed randomly, and most of parts look filled bulk morphology. The density of the gel obtained from the present polystyrene-based copolymers was estimated to be 200 mg/cm(3), which implies existence of vacancies without observation in the SEM image, suggesting the extremely fine cell structure.

Tin-polymer composite on a rotating drum as a high repetition rate laser target for extreme ultraviolet generation Reviewed

Y Yasuda, QC Gu, K Nagai, M Nakai, T Norimatsu, S Fujioka, H Nishimura, M Nakatsuka

FUSION SCIENCE AND TECHNOLOGY 49 ( 4 ) 691 - 694 2006.5

High repetition rate irradiation of a laser on target is necessary for practical operation of an extreme ultraviolet (EUV) light source. A rotating drum with a tin composite film was fabricated for this purpose. Uniformly tin-dispersed plastic film was prepared from hydroxypropyl cellulose (HPC) and tin source solution of SnCl4/ethanol/H2O. It was transparent in the visible to near infrared region. The film was coated on an aluminum rotating drum from HPC-Sn solution. When this solution was coated on aluminum rotating target drum directly, the drum was corroded. Therefore an alternative method was developed starting with tin(tertbutoxide) instead of SnCl4. The later solution was used for coating on aluminum rotating target drum directly.

Low-density-plastic-foam capsule of resorcinol/formalin and (phloroglucinolcarboxylic acid)/formalin resins for fast-ignition realization experiment (FIREX) in laser fusion research Reviewed

F Ito, K Nagai, M Nakai, T Norimatsu, A Nikitenko, S Tolokonnikov, E Koresheva, T Fujimura, H Azechi, K Mima

JAPANESE JOURNAL OF APPLIED PHYSICS PART 2-LETTERS & EXPRESS LETTERS 45 ( 8-11 ) L335 - L338 2006.3

In this report, we describe fuel (deuterium and tritium) Capsule preparation for the fast-ignition realization experiment (FIREX) in laser fusion research. The required diameter and thickness of the capsule are 500 and 20 pill, respectively. The material Should be plastics with low-density foam. We have prepared such a capsule using (1) a new material of (phloroglucinolcarboxylic acid)/formalin resin to control the kinematic viscosity of the precursor, (2) the phase-transfer-catalyzed gelation process to maintain the density matching of the emulsion. The obtained foam capsule had a fine structure of 180 run (outer surface) to 220 run (inner surface) size and a uniform thickness reaching the resolution limit of optical analysis (similar to 0.5 mu m).

Cool-down performance of the apparatus for the cryogenic target of the FIREX project Reviewed

A. Iwamoto, R. Maekawa, T. Mito, M. Okamoto, O. Motojima, S. Sugito, K. Okada, M. Nakai, T. Norimatsu, K. Nagai

Fusion Engineering and Design 81 ( 8-14 PART B ) 1647 - 1652 2006.2

The apparatus for cryogenic target experiments of the Fast Ignition Realization EXperiment (FIREX) project has been developed at the National Institute for Fusion Science (NIFS). To achieve the target specifications for the project, the foam shell method has been proposed. The Institute of Laser Engineering (ILE), Osaka University and NIFS have started a cooperative study of the method. NIFS is responsible for the demonstration of the fuel layering process. The first cool-down test of the apparatus was conducted. Its cool-down performance is described in this paper. © 2005 Elsevier B.V. All rights reserved.

Angular distribution control of extreme ultraviolet radiation from laser-produced plasma by manipulating the nanostructure of low-density SnO2 targets Reviewed

K Nagai, QC Gu, ZZ Gu, T Okuno, S Fujioka, H Nishimura, YZ Tao, Y Yasuda, M Nakai, T Norimatsu, Y Shimada, M Yamaura, H Yoshida, M Nakatsuka, N Miyanaga, K Nishihara, Y Izawa

APPLIED PHYSICS LETTERS 88 ( 9 ) 2006.2

We have found that the divergence of a relatively monochromatic extreme ultraviolet (EUV) emission from a laser-produced plasma can be manipulated by changing the target morphology which is a porous low-density tin oxide (SnO2) structure. The fundamental light of a Nd-YAG laser was irradiated on the target with laser intensity of similar to 10(11) W/cm(2) and pulse duration of 10 ns. The nanostructure and density of the targets were tuned by a combination of colloidal polymer template and sol-gel processes [Gu, Nagai, Norimatsu, Fujioka, Nishimura, Nishihara, Miyanaga, and Izawa, Chem. Mater. 17, 1115 (2005)], which has a merit in large-scale preparation. When the target has an open cell nanostructure, the EUV emission directed predominantly along target normal, while a closed cell target exhibited divergent emission. The angular distribution may be affected by the orientation of the microstructured initial target, and this phenomenon can be applied to wavefront control of EUV emission.

Ultrafast x-ray imaging with sliced sampling streak cameras Reviewed

TX Huang, M Nakai, H Shiraga, H Azechi, TX Huang, YK Ding, ZJ Zheng

REVIEW OF SCIENTIFIC INSTRUMENTS 77 ( 2 ) 2006.2

Polymorphic tin dioxide synthesis via sol-gel mineralization of ethyl-cyanoethyl cellulose lyotropic liquid crystals Reviewed

Qincui Gu, Keiji Nagai, Mitsuo Nakai, Takayoshi Norimatsu

Colloid and Polymer Science 284 ( 4 ) 429 - 434 2006.1

The polymorphic tin dioxide (SnO2) was synthesized by calcinating the sol-gel mineralized hybrid of the tin source solution (SnC14/ethanol/H2O) and the lyotropic liquid crystal of ethyl-cyanoethyl cellulose((E-CE)C)/acrylic acid (AA). The sub-micrometer SnO2 spheres with bimodal distribution at 370 and 860 nm were obtained after calcinating the hybrid at 400 °C for 5 h. When the hybrid was exposed to ultraviolet first and then calcinated the flying-saucer-like SnO2 was formed. The exposure time was found to influence the morphology of the as-prepared SnO2. Except for the spherical and the flying-saucer-like SnO2, a small amount of well-developed polyhedral SnO2 was also observed in the as-prepared samples. On this basis, the lyotropic liquid crystal of (E-CE)C/AA afforded a novel route to obtain polymorphic SnO2. © Springer-Verlag 2005.

Equation of state of diamond under shock compression up to 2 TPa Reviewed

H. Nagao, K. G. Nakamura, K. Kondo, N. Ozaki, T. Ono, K. Takamatsu, K. A. Tanaka, K. Nagai, M. Nakai, K. Wakabayashi, K. Okada, M. Yoshida

Shock Compression of Condensed Matter - 2005, Pts 1 and 2 845 111 - 114 2006

The equation of state of diamond was studied using laser-driven shock waves in a terapascal region between 0.5 and 2 TPa. Strong shock waves were generated by direct irradiation of a 2.5 ns laser pulse on an Al driver plate. The shock wave velocities in the diamond and Al were measured optically. Particle velocities and pressures were obtained using impedance matching and the known Al Hugoniot. The dependence of U-s(Dia)(u(p)(Dia)) obtained for single crystalline diamond is well-approximated by U-s(Dia)=11.2+1.2u(p)(Dia) for the obtained Hugoniot data, all previous experimental data, and the bulk sound velocity.

Observation of Xenon EUV Spectra in Compact Helical System Reviewed

SUZUKI Chihiro, NISHIMURA Hiroaki, SONG Mi-Young, KATO Takako, OKAMURA Shoichi, MORE Richard, NISHIHARA Katsunobu, NAKAI Mitsuo, SHIGEMORI Keisuke, FUJIOKA Shinsuke, OGAWA Hiroaki, SASAKI Akira

Journal of Plasma and Fusion Research SERIES 7 73 - 76 2006

Towards realization of hyper-velocities for impact fast ignition Reviewed

M. Murakami, H. Nagatomo, T. Sakaiya, H. Azechi, S. Fujioka, H. Shiraga, M. Nakai, K. Shigemori, H. Saito, S. Obenschain, M. Karasik, J. Gardner, J. Bates, D. Colombant, J. Weaver, Y. Aglitskiy

Plasma Physics and Controlled Fusion 47 ( 12 B ) B815 - B822 2005.12

A new ignition scheme, impact fast ignition (IFI), is studied, in which the compressed DT main fuel is to be ignited by impact with another fraction of separately imploded DT fuel, which is accelerated in the hollow conical target. The first and distinct milestone in the IFI scenario is the demonstration of such a hyper-velocity, of the order of 108 cm s-1. Two-dimensional hydrodynamic simulation results obtained in full geometry using plastic instead of DT fuel are presented, in which some key physical parameters for the impact shell dynamics, such as an implosion velocity of 108 cm s-1, a compressed density of 300-400 g cm-3 and a converted temperature greater than 5 keV, are demonstrated. A preliminary experimental result with a planar target is presented to show the highest velocity, 6 × 107 cm s-1, ever achieved. © 2005 IOP Publishing Ltd.

Dynamic imaging of 13.5 nm extreme ultraviolet emission from laser-produced Sn plasmas Reviewed

Y Tao, H Nishimura, T Okuno, S Fujioka, N Ueda, M Nakai, K Nagai, T Norimatsu, N Miyanaga, K Nishihara, Y Izawa

APPLIED PHYSICS LETTERS 87 ( 24 ) 2005.12

Temporally resolved imaging of 13.5 nm extreme ultraviolet (EUV) emission from laser-produced Sn plasmas was experimentally investigated with a monochromatic EUV imager. Absorption caused by the surrounding plasma was eliminated by adopting a stripe Sn target laminated on a plastic film so that the CH plasma tamped lateral expansion of the Sn plasma. The experimental results revealed that reabsorption induced by plasma, both in EUV emission-dominant and long scale coronal regions, plays an key role in extracting the EUV light from the plasma efficiently. (c) 2005 American Institute of Physics.

Opacity effect on extreme ultraviolet radiation from laser-produced tin plasmas Reviewed

S Fujioka, H Nishimura, K Nishihara, A Sasaki, A Sunahara, T Okuno, N Ueda, T Ando, YZ Tao, Y Shimada, K Hashimoto, M Yamaura, K Shigemori, M Nakai, K Nagai, T Norimatsu, T Nishikawa, N Miyanaga, Y Izawa, K Mima

PHYSICAL REVIEW LETTERS 95 ( 23 ) 2005.12

Opacity effects on extreme ultraviolet (EUV) emission from laser-produced tin (Sn) plasma have been experimentally investigated. An absorption spectrum of a uniform Sn plasma generated by thermal x rays has been measured in the EUV range (9-19 nm wavelength) for the first time. Experimental results indicate that control of the optical depth of the laser-produced Sn plasma is essential for obtaining high conversion to 13.5 nm-wavelength EUV radiation; 1.8% of the conversion efficiency was attained with the use of 2.2 ns laser pulses.

Resorcinol-formalin foam balls via gelation of emulsion using phase-transfer catalysts Reviewed

Fuyumi Ito, Keiji Nagai, Mitsuo Nakai, Takayoshi Norimatsu

Macromolecular Chemistry and Physics 206 ( 21 ) 2171 - 2176 2005.11

Highly spherical (98.5%) low-density foam balls with 1-mm diameters were fabricated from a density-matched emulsion consisting of a resorcinol/formalin aqueous solution and a (mineral oil and carbon tetrachloride) mixture. Phase-transfer catalysts of carboxylic acid were utilized to induce gelation of the emulsion. The gelation process was monitored by a mechanical test. Gelation forming ball shapes happened within 20-30 min, depending on the catalysts, at room temperature. The gelation time decreased with high-catalyst concentration. Acids with long alkyl chains did not induce gelation and no balls were obtained. The gelated balls were dried to obtain foam via an exchange of the solvent with 2-propanol and extraction using the supercritical fluid CO2. The density obtained from the catalyst was 0.15-0.16 g · cm-3. SEM images revealed surface membrane formation, which can be explained by local concentration at the interface of W/O. We observed different bulk foam cell sizes, which may depend on the catalysts and, therefore, on the different gelation rates. © 2005 WILEY-VCH Verlag GmbH &amp
Co. KGaA, Weinheim.

Foam materials for cryogenic targets of fast ignition realization experiment (FIREX) Reviewed

K Nagai, H Azechi, F Ito, A Iwamoto, Y Izawa, T Johzaki, R Kodama, K Mima, T Mito, M Nakai, N Nemoto, T Norimatsu, Y Ono, K Shigemori, H Shiraga, KA Tanaka

NUCLEAR FUSION 45 ( 11 ) 1277 - 1283 2005.11

Development of foam materials for cryogenically cooled fuel targets is described in this paper. The fabrication development was initiated as a part of the fast ignition realization experiment (FIREX) project at the ILE, Osaka University under a bilateral collaboration between OsakaUniversity and National Institute for Fusion Science (NIFS). For the first stage of FIREX (FIREX-1), a foam cryogenic target was designed in which low-density foam shells with a conical light guide will be fuelled through a narrow pipe and will be cooled down to the cryogenic temperature. Acrylic polymer, resorcinol-formaldehyde (RF) resin, poly(4-methyl-1-pentene) (PMP), and polystyrene-based crosslinking polymer have been investigated as supporting materials for cryogenic fuel. The properties of the material and the present status of the material development are summarized.

Characterization of density profile of laser-produced Sn plasma for 13.5 nm extreme ultraviolet source Reviewed

Y Tao, H Nishimura, S Fujioka, A Sunahara, M Nakai, T Okuno, N Ueda, K Nishihara, N Miyanaga, Y Izawa

APPLIED PHYSICS LETTERS 86 ( 20 ) 2005.5

We investigated the electron density profile corresponding to the dominant extreme ultraviolet (EUV) emission from a laser-produced Sn plasma using a combination of a green and an UV interferometer. A comparison between experimental results and a one-dimensional radiation hydrodynamic simulation shows reasonable agreement, and the discrepancy could be attributed to three-dimensional plasma expansion. It was found that, due to opacity effects, most of the EUV light comes from an under-dense plasma region. (c) 2005 American Institute of Physics.

Present status of fast ignition research and prospects of FIREX project Reviewed

K Mima, H Azechi, Y Johzaki, Y Kitagawa, R Kodama, Y Kozaki, N Miyanaga, K Nagai, H Nagatomo, M Nakai, H Nishimura, T Norimatsu, H Shiraga, KA Tanaka, Y Izawa, Y Nakao, H Sakagami

FUSION SCIENCE AND TECHNOLOGY 47 ( 3 ) 662 - 666 2005.4

This is the review on the laser fusion research at Institute of Laser Engineering of Osaka University. Since 1996, we have concentrated our efforts on fast ignition laser fusion research. By constructing 100 TW and 1 Peta watt lasers, experiments on relativistic laser plasma interactions related to fast ignition and pellet implosion and heating have been carried out. The results indicate that imploded core plasma is heated with relatively high coupling efficiency. According to the above results, we started the FIREX (Fast Ignition Realization Experiment) project for demonstrating ignition and burn with a multi 10kJ short pulse laser. The future prospects of the project are presented in this paper.

Characterization of extreme ultraviolet emission from laser-produced spherical tin plasma generated with multiple laser beams Reviewed

Y Shimada, H Nishimura, M Nakai, K Hashimoto, M Yamaura, Y Tao, K Shigemori, T Okuno, K Nishihara, T Kawamura, A Sunahara, T Nishikawa, A Sasaki, K Nagai, T Norimatsu, S Fujioka, S Uchida, N Miyanaga, Y Izawa, C Yamanaka

APPLIED PHYSICS LETTERS 86 ( 5 ) 2005.1

Spherical solid tin targets were illuminated uniformly with twelve beams from the Gekko XII laser system to create spherical plasmas, and the extreme ultraviolet (EUV) emission spectra from the plasmas were measured. The highest conversion efficiency of 3% to 13.5 nm EUV light in 2% bandwidth was attained for an irradiance of around 5 x 10(10) W/cm(2). The experimental results were reproduced fairly well using a theoretical model taking the power balance in the plasma into consideration. (C) 2005 American Institute of Physics.

Petawatt-laser direct heating of uniformly imploded deuterated-polystyrene shell target

Yoneyoshi Kitagawa, Yasuhiko Sentoku, Shin Akamatsu, Wataru Sakamoto, Kazuo A. Tanaka, Ryosuke Kodama, Hiroaki Nishimura, Yuichi Inubushi, Mitsuo Nakai, Takeshi Watari, Takayoshi Norimatsu, Atsushi Sunahara

Physical Review E - Statistical, Nonlinear, and Soft Matter Physics 71 ( 1 ) 2005.1

A uniformly imploded deuterated polystyrene (CD) shell target is fast-heated by a Petawatt (PW) laser without cone guide. The best illumination timing is found to be in a narrow region around 80±20 picoseconds from the onset of the stagnation phase, where thermal neutrons are enhanced four to five times by the PW laser of energy less than 10% of the implosion laser. The timing agrees with the timings of enhancement of the x-ray emission from the core and reduction of the bremsstrahlung radiation from scattered hot electrons. The PW laser, focused to the critical density point, generates the energetic electrons within as narrow an angle as 30°, which then heats the imploded CD shell to enhance thermal neutrons. These results first demonstrate that the PW laser directly heats the imploded core without any conelike laser guide. © 2005 The American Physical Society.

Petawatt-laser direct heating of uniformly imploded deuterated-polystyrene shell target Reviewed

Y Kitagawa, Y Sentoku, S Akamatsu, W Sakamoto, KA Tanaka, R Kodama, H Nishimura, Y Inubushi, M Nakai, T Watari, T Norimatsu, A Sunahara

PHYSICAL REVIEW E 71 ( 1 ) 2005.1

A uniformly imploded deuterated polystyrene (CD) shell target is fast-heated by a Petawatt (PW) laser without cone guide. The best illumination timing is found to be in a narrow region around 80 20 picoseconds from the onset of the stagnation phase, where thermal neutrons are enhanced four to five times by the PW laser of energy less than 10% of the implosion laser. The timing agrees with the timings of enhancement of the x-ray emission from the coreand reduction of the bremsstrahlung radiation from scattered hot electrons. The PW laser, focused to the critical density point, generates the energetic electrons within as narrow an angle as 30degrees, which then heats the imploded CD shell to enhance thermal neutrons. These results first demonstrate that the PW laser directly heats the imploded core without any conelike laser guide.

Equation-of-state measurements for polystyrene at multi-TPa pressures in laser direct-drive experiments Reviewed

N. Ozaki, T. Ono, K. Takamatsu, K. A. Tanaka, M. Nakano, T. Kataoka, M. Yoshida, K. Wakabayashi, M. Nakai, K. Nagai, K. Shigemori, T. Yamanaka, K. Kondo

Physics of Plasmas 12 ( 12 ) 1 - 4 2005

Equation-of-state (EOS) measurements for polystyrene in TPa (10 Mbar) pressure regions are presented. Polystyrene Hugoniot data were obtained up to 2.7 TPa using impedance matching techniques with laser direct drive at the GEKKO/HIPER laser facility [N. Miyanaga, in Proceedings of the 18th International Conference on Fusion Energy (IAEA, Sorrento, Italy, 2001), IAEA-CN-77] The results were compared with theoretical models and previous experimental data and found to be in good agreement with the previous data obtained by different drive and diagnostic techniques. © 2005 American Institute of Physics.

Petawatt laser direct heating of imploded plasmas and thermal neutron enhancement

Yoneyoshi Kitagawa, Shin Akamatsu, Wataru Sakamoto, Kazuo A. Tanaka, Ryosuke Kodama, Hiroaki Nishimura, Yuichi Inubushi, Mitsuo Nakai, Takeshi Watari, Takayoshi Norimatsu, Atsushi Sunahara, Yasuhiko Sentoku

Inertial Fusion Sciences and Applications 2003 387 - 393 2004.12

To heat an uniformly imploded deuterated polystyrene shell target, Petawatt laser illumination timing is scanned from the implosion, through stagnation to expansion or disruption phases. After 80 ± 20 picosecond from the onset of the stagnation phase but yet within it, thermal neutrons are four times enhanced from l × 106. The timing exactly agrees with that of X-ray emission from the core. In the stagnation phase, beam fusion neutrons reduced to 1.5 times the thermal one. Temporal behaviours of Bremsstrahlung due to hot electrons and laser backscatterings support the the timing.

Two-dimensional ablation density measurement relevant to Rayleigh-Taylor instability with fresnel phase zone plate

Yohei Tamari, Hiroshi Azechi, Shinsuke Fujioka, Tatsuhiro Sakaiya, Hiroyuki Shiraga, Mitsuo Nakai, Keisuke Sigemori

Inertial Fusion Sciences and Applications 2003 182 - 185 2004.12

Fresnel phase zone plate (FPZP) can image hard x rays (>5 keV) with high spatial resolution of a few μm. In FPZP image, a structured background overlaps on an image. The image intensity profile cannot be obtained accurately. We have resolved this problem of structured background, and obtained plasma intensity profile within 10% error. Using FPZP, the plasma density measurement experiment has been demonstrated. The density profile of in-flight polystyrene plasma has been measured at several different times. The experimental density profiles have been compared with the calculated results by 1-D simulation code. The experiment data agreed with the simulation results.

Fast plasma heating in a cone-attached geometry - towards fusion ignition Reviewed

R Kodama, H Azechi, H Fujita, H Habara, Y Izawa, T Jitsuno, T Jozaki, Y Kitagawa, K Krushelnick, T Matsuoka, K Mima, N Miyanaga, K Nagai, H Nagatomo, M Nakai, H Nishimura, T Norimatsu, P Norreys, K Shigemori, H Shiraga, A Sunahara, KA Tanaka, M Tanpo, Y Toyama, K Tsubakimoto, T Yamanaka, M Zepf

NUCLEAR FUSION 44 ( 12 ) S276 - S283 2004.12

We have developed a PW (0.5 ps/500J) laser system to demonstrate fast heating of imploded core plasmas using a hollow cone shell target. Significant enhancement of thermal neutron yield has been realized with PW-laser heating, confirming that the high heating efficiency is maintained as the short-pulse laser power is substantially increased to a value nearly equivalent to the ignition condition. It appears that the efficient heating is realized by the guiding of the PW laser pulse energy within the hollow cone and by self-organized relativistic electron transport. Based on the experimental results, we are developing a 10kJ-PW laser system to study the fast heating physics of high-density plasmas at an ignition-equivalent temperature.

Suppression of the Rayleigh-Taylor instability and its implication for the impact ignition Reviewed

H Azechi, H Shiraga, M Nakai, K Shigemori, S Fujioka, T Sakaiya, Y Tamari, K Ohtani, M Murakami, A Sunahara, H Nagatomo, K Nishihara, N Miyanaga, Y Izawa

PLASMA PHYSICS AND CONTROLLED FUSION 46 B245 - B254 2004.12

The Rayleigh-Taylor (RT) instability with material ablation through an unstable interface is the key physics that determines the success or failure of inertial fusion energy (IFE) generation, as the RT instability potentially quenches ignition and burn by disintegrating the IFE target. We present two suppression schemes of the RT growth without significant degradation of the target density. The first scheme is to generate a double ablation structure in high-Z doped plastic targets. In addition to the electron ablation surface, a new ablation surface is created by x-ray radiation from the high-Z ions. Contrary to the previous thought, the electron ablation surface is almost completely stabilized by extremely high flow velocity. On the other hand, the RT instability on the radiative ablation surface is significantly moderated. The second is to enhance the nonlocal nature of the electron heat transport by illuminating the target with long wavelength laser light, whereas the high ablation pressure is generated by irradiating with short wavelength laser light. The significant suppression of the RT instability may increase the possibility of impact ignition which uses a high-velocity fuel colliding with a preformed main fuel.

Temporally resolved Schwarzschild microscope for the characterization of extreme ultraviolet emission in laser-produced plasmas

Y Tao, M Nakai, H Nishimura, S Fujioka, T Okuno, T Fujiwara, N Ueda, N Miyanaga, Y Izawa

REVIEW OF SCIENTIFIC INSTRUMENTS 75 ( 12 ) 5173 - 5176 2004.12

A temporally resolved monochromatic extreme ultraviolet (EUV) imager has been developed for use in EUV radiation source research. The imager consists of a Schwarzschild microscope, with near-normal-incident Mo/Si multilayer mirrors adjusted for 13.5 nm and 4% bandwidth, and an x-ray streak camera (XSC). The spatial resolution of the microscope was limited by the image detector's resolution to 3.5 mum for the CCD camera and 15 mum for the XSC, respectively, for a field of view of 1.2 mm. With the high photon collection efficiency, clear streak images could be obtained on a single-shot basis with laser pulse energy as low as 50 mJ at an intensity of 1x10(10) W/cm(2). Expansion behavior of the EUV emission region was successfully observed for laser-produced Sn plasmas. (C) 2004 American Institute of Physics.

Suppression of the Rayleigh-Taylor instability due to self-radiation in a multiablation target

Shinsuke Fujioka, Atsushi Sunahara, Katsunobu Nishihara, Naofumi Ohnishi, Tomoyuki Johzaki, Hiroyuki Shiraga, Keisuke Shigemori, Mitsuo Nakai, Tadashi Ikegawa, Masakatsu Murakami, Keiji Nagai, Takayoshi Norimatsu, Hiroshi Azechi, Tatsuhiko Yamanaka

Physical Review Letters 92 ( 19 ) 1 - 195001 2004.5

The suppression of the Rayleigh-Taylor instability that occurs due to self-Radiation in a multiablation target was investigated. It was demonstrated that in a high-Z doped plastic target, two ablation surfaces were formed separately, one driven by thermal radiation and the other driven by electron conduction. It was found that the growth of the Rayleigh-Taylor instability was significantly suppressed on the radiation-driven ablation surface inside the target becasue of a large ablation velocity and long density scale length. Using a brominated plastic target, a significant reduction in growth rate was observed.

Suppression of Rayleigh-Taylor instability due to radiative ablation in brominated plastic targets

S Fujioka, A Sunahara, N Ohnishi, Y Tamari, K Nishihara, H Azechi, H Shiraga, M Nakai, K Shigemori, T Sakaiya, M Tanaka, K Otani, K Okuno, T Watari, T Yamada, M Murakami, K Nagai, T Norimatsu, Y Izawa, S Nozaki, YW Chen

PHYSICS OF PLASMAS 11 ( 5 ) 2814 - 2822 2004.5

Suppression of hydrodynamic instabilities is very crucial for the ultimate goal of inertial fusion energy (IFE). A high-Z doped plastic of CHBr (brominated polystyrene) ablator is a very promising candidate to suppress the ablative Rayleigh-Taylor (RT) instability in a directly laser-driven IFE target. When a CHBr target is irradiated by intense laser beams, bromine atoms in the corona plasma emit strong radiation. The strong radiation drives the radiative ablation front inside the CHBr targets. This radiative ablation in the high-Z doped plastic target has many advantages for the suppression of the growth of the RT instability in analogy to the indirect-drive approach, i.e., large mass ablation rate, long density scale length and low peak density. Two-dimensional (2D) hydrodynamic simulation shows significant suppression of the RT instability in a CHBr target compared to an undoped polystyrene (CH) target. RT growth rate, calculated theoretically using the Betti-Goncharov procedure with a one-dimensional radiation-hydrodynamic simulation code, is in good agreement with the 2D calculations. Experiments were performed at the GEKKO XII- [C. Yamanaka , IEEE J. Quantum Electron. QE-17, 1639 (1981)] HIPER (High Intensity Plasma Experimental Research) laser facility. The trajectory of a laser-driven CHBr target observed in the experiment was reproduced fairly well by the simulation. The radiative ablation front formed inside a directly laser-driven CHBr target was clearly observed for the first time. The strong suppression of the RT instability in the CHBr target was confirmed using the face-on and side-on x-ray backlighting technique. The high-Z doped ablator can be applied to high density cryogenic deuterium-deuterium and deuterium-tritium compression, because the hydrogen-isotopes are nearly transparent to x rays, which are transmitted through the ablator from the laser-irradiation side. (C) 2004 American Institute of Physics.

GEKKO/HIPER-driven shock waves and equation-of-state measurements at ultrahigh pressures

N Ozaki, KA Tanaka, T Ono, K Shigemori, M Nakai, H Azechi, T Yamanaka, K Wakabayashi, M Yoshida, H Nagao, K Kondo

PHYSICS OF PLASMAS 11 ( 4 ) 1600 - 1608 2004.4

The GEKKO/HIPER-laser [N. Miyanaga et al., in Proceedings of the 18th International Conference on Fusion Energy (IAEA, Sorrento, Italy, 2001), IAEA-CN-77] driven shock experiments were characterized in detail for studies on equation-of-state (EOS) at ultrahigh pressures. High-quality shock waves were produced with the bundled 9 laser beams optically smoothed by spectral dispersion technique and Kinoform phase plates. The laser beams were directly focused on targets at up to an intensity of 10(14) W/cm(2) or higher with a wavelength of 351 nm and a duration of 2.5 us. Key issues on dynamic EOS research; the spatial uniformity and temporal steadiness of shock wave were estimated, and the preheating problem was also investigated by measurements of the self-emission and reflectivity from target rear surface. The experimental and analytical methods were validated by using double-step targets consisting of two Hugoniot standard metals. Extreme pressures only accessed in nuclear explosion experiments were generated with reproducibility and good accuracy using the laser direct-drive experimental system, for Al, Cu, polystyrene, and Ta. It was indicated that new and reliable EOS data at the ultrahigh pressures could be provided for materials ranging from low to high initial density by the laser direct-drive experimental technique. (C) 2004 American Institute of Physics.

Present status and future prospects of laser fusion research at ILE Osaka university Reviewed

K Mima, KA Tanaka, R Kodama, T Johzaki, H Nagatomo, H Shiraga, Y Sentoku, N Miyanaga, H Azechi, M Nakai, T Norimatu, K Nagai, J Sunahara, K Nishihara, T Taguchi, H Sakagami

PLASMA SCIENCE & TECHNOLOGY 6 ( 1 ) 2179 - 2184 2004.2

Reviewed are the present status and future prospects of the laser fusion research at the ILE Osaka. The Gekko XII and Peta Watt laser system have been operated for investigating the implosion hydrodynamics, fast ignition, and the relativistic laser plasma interactions and so on. In particular, the fast ignition experiments with cone shell target have been in progress as the UK and US-Japan collaboration programs. In the experiments, the imploded high density plasmas are heated by irradiating 500 J level peta-watt laser pulse. The thermal neutron yield is found to increase by three orders of magnitude by injecting the peta-watt laser into the cone shell target. The Rayleigh-Taylor instability experiment results are also reviewed is this paper.

Characterization of extreme UV radiation in laser produced plasma for use in lithography Reviewed

Nishimura H, Shigemori K, Nakai M, Fujioka S, Shimada Y, Hashimoto K, Yamaura M, Uchida S, Matsui R, Hibino T, Okuno T, Tao Y, Nagai K, Norimatsu T, Nagatomo H, Zhakhovckii V, Furukawa H, Sunahara A, Kawamura T, Murakami M, Nishihra K, Miyanaga N, Nakatsuka M, Izawa Y

Inertial Fusion Sciences and Applications 2003 1077 - 1080 2004

A new research project on extreme ultraviolet (EUV) source development has been started utilizing resources of laser fusion research. The main task is to provide a scientific basis for generating efficient, debris-free, high power EUV plasma source for production of semiconductor devices. Experimental data sets are obtained not only with Joule-class laser but also with GEKKO-XII to improve detailed atomic model included in a radiation hydrodynamic code and to find an optimum condition for source plasma generation. Spherical solid-tin and tin-oxide targets were illuminated uniformly with twelve beams from GEKKO XII to create one-dimensional (1-D) spherical plasmas. The highest conversion efficiency of a few % to 13.5 nm EUV light in 2% bandwidth was attained at irradiance of 1-2×1011 W/cm2. No significant difference was found between laser wavelengths of one μm and a half μm.

Estimation of emission efficiency for laser-produced EUV-plasmas Reviewed

T Kawamura, A Sunahara, K Gamada, K Fujima, F Koike, H Furukawa, T Nishikawa, A Sasaki, T Kagawa, R More, T Kato, M Murakami, Zhakhovskii, V, H Tanuma, T Fujimoto, Y Shimada, M Yamaura, K Hashimoto, S Uchida, C Yamanaka, T Okuno, T Hibino, N Ueda, R Matsui, YZ Tao, M Nakai, K Shigemori, S Fujioka, K Nagai, T Norimatsu, H Nishimura, K Nishihara, N Miyanaga, Y Izawa

EMERGING LITHOGRAPHIC TECHNOLOGIES VIII 5374 918 - 925 2004

Extreme Ultra Violet (EUV) light source produced by laser irradiation emits not only the desired EUV light of 13 similar to 14 nm (about 90 eV) but also shorter x-rays. For example, emissions around. 4 similar to 8 nm (about 150 similar to 300 eV) and 1 similar to 2.5 nm (about 0.5 similar to 1.2 keV) are experimentally observed from Sn and/or SnO2 plasmas. These emissions are correspond to the N-shell and M-shell transitions, respectively. From the view point of energy balance and efficiency, these transitions should be suppressed. However, they may, to some extent, contribute to provide the 5p and 4f levels with electrons which eventually emit the EUV light and enhance the intensity. To know well about radiative properties and kinematic of the whole plasma, atomic population kinetics and spectral synthesis codes have been developed. These codes can estimate the atomic population with nl-scheme and spectral shapes of the EUV light. Radiation hydrodynamic simulation have been proceeding in this analysis. Finally, the laser intensity dependence of the conversion efficiency calculated by these codes agrees with that of the corresponding experimental results.

Characterization of GEKKO/HIPER-Driven Shock Waves for Equation-of-State Experiments in Ultra-High-Pressure Regime

Takamatsu Kikuo, Yamanaka Tatsuhiko, Azechi Hiroshi, Miyanaga Noriaki, Nakai Mitsuo, Ono Takatoshi, Nagai Keiji, Shigemori Keisuke, Ozaki Norimasa, Tanaka Kazuo A.

Journal of Plasma and Fusion Research vol. 80, pp. 486-491 ( 6 ) 486 - 491 2004

Experimental study on ablative stabilization of Rayleigh-Taylor instability of laser-irradiated targets Reviewed

K Shigemori, T Sakaiya, K Otani, S Fujioka, M Nakai, H Azechi, H Shiraga, Y Tamari, K Okuno, A Sunahara, H Nagatomo, M Murakami, K Nishihara, Y Izawa

HIGH-POWER LASER ABLATION V, PTS 1 AND 2 5448 634 - 641 2004

Hydrodynamic instabilities are key issues of the physics of inertial confinement fusion (ICF) targets. Among the instabilities, Rayleigh-Taylor (RT) instability is the most important because it gives the largest growth factor in the ICF targets. Perturbations on the laser irradiated surface grow exponentially, but the growth rate is reduced by ablation flow. The growth rate gamma is written as Takabe-Betti formula: gamma = (kg/(1+kL))(1/2). -betakm/rho(a), where k is wave number of the perturbation, g is acceleration, L is density scale-length, beta is a coefficient, m is mass ablation rate per unit surface, and rho(a), is density at the ablation front. We experimentally measured all the parameters in the formula for polystyrene (CH) targets. Experiments were done on the RIPER laser facility at Institute of Laser Engineering, Osaka University. We found that the beta value in the formula is similar to 1.7, which is in good agreements with the theoretical prediction, whereas the beta for certain perturbation wavelengths are larger than the prediction. This disagreement between the experiment and the theory is mainly due to the deformation of the cutoff surface, which is created by non-uniform ablation flow from the ablation surface. We also found that high-Z doped plastic targets have multiablation structure, which can reduce the RT growth rate. When a low-Z target with high-Z dopant is irradiated by laser, radiation due to the high-Z dopant creates secondary ablation front deep inside the target. Since, the secondary ablation front is ablated by x-rays, the mass ablation rate is larger than the laser-irradiated ablation surface, that is, further reduction of the RT growth is expected. We measured the RT growth rate of Br-doped polystyrene targets. The experimental results indicate that of the CHBr targets show significantly small growth rate, which is very good news for the design of the ICF targets.

Experimental study on basic properties of laser-produced EUV plasmas on GEKKO-XII laser facility Reviewed

K Shigemori, M Nakai, Y Shimada, M Yamaura, K Hashimoto, S Fujioka, H Nishimura, S Uchida, A Sunahara, K Nishihara, N Miyanaga, Y Izawa

EMERGING LITHOGRAPHIC TECHNOLOGIES VIII 5374 971 - 978 2004

Extremely ultraviolet (EUV) light at around 13.5 nm of wavelength is the most probable candidate of the light source for lithography for semiconductors of next generation. We have been studying about the EUV light source from laser-produced plasma. Detailed understanding of the EUV plasma is required for developments of modeling with simulation codes. Several parameters should be experimentally measured to develop the important issues in the simulation codes. We focused on density profile, properties of EUV emission, and opacity of the laser-produced plasmas. We present recent experimental results on these basic properties of the laser-produced EUV plasmas.

Rayleigh-taylor instability and its reduction in laser-accelerated targets Reviewed

Shiraga H, Shigemori K, Nakai M, Sakaiya T, Fujioka S, Tamari Y, Azechi H, Nishihara K, Sunahara A, Nagatomo H, Ikegawa T, Ohnishi N, Nagai K, Norimats T, Yamanaka T

Inertial Fusion Sciences and Applications 2003 115 - 120 2004

Rayleigh-Taylor (RT) instability is of great importance in laser fusion because its growth degrades integrity of the imploding shell and may lower the density of the imploded core plasma. The dispersion relation of RT growth rate described by the modified Bodner-Takabe formula have been intensively investigated with Gekko-XII-HIPER laser at ILE, Osaka University. The growth rate is strongly dependent on the density structure of the accelerated target, and hence, there is a possibility to reduce RT growth by controlling the energy transport in the laser-driven target. We recently demonstrated two types of technique to reduce RT growth: one is double ablation in which radiation transport is utilized, and the other is two-color laser irradiation in which induced nonlocal electron transport is enhanced. Both of them will be effective in reducing the RT instability growth in inertial fusion targets.

Reduction of the Rayleigh-Taylor instability growth with multi-color laser irradiation Reviewed

Shigemori K, Otani K, Sakaiya T, Sunahara A, Fujioka S, Nakai M, Shiraga H, Azechi H, Nishihara K

Inertial Fusion Sciences and Applications 2003 186 - 189 2004

Theoretical modeling of laser-produced plasmas for development of extreme UV radiation source for lithography Reviewed

Nishihara K, Nishikawa T, Sasaki A, Kawamura T, Sunahara A, Furukawa H, Murakami M, Nishimura H, Shimada Y, Nakai M, Fujioka S, Shigemori K, Uchida S, Fujima K, More R, Koike F, Kagawa T, Zhakhovskii V, Hashimoto K, Yamaura M, Matsui R, Hibino T, Okuno T, Tao Y, Sohnatzadeh F.L, Nagai K, Norimatsu T, Tanuma H, Miyanaga N, Izawa Y

Inertial Fusion Sciences and Applications 2003 1069 - 1073 2004

A design window of laser and plasma parameters required for an extreme ultraviolet (EUV) radiation source for practical application for the next generation of lithography has been introduced. We present a simple analytical model of conversion efficiency from laser energy to radiation energy with a wavelength of 13.5 nm with 2 % bandwidth, by considering power balance of laser produced high-z plasma. We also investigate dependence of the EUV emission from tin and tin-oxide plasmas on laser intensity and wavelength in spherical geometry using the GEKKO XII laser system. It is found that the conversion efficiency into a 2% bandwidth about 13.5 nm has a maximum of a few percent near the laser intensity 10 11 W/cm 2. The efficiency is about the same for 1.053 μm and 0.527 μm laser wavelengths. A scaling law of the conversion efficiency on the laser intensity obtained agrees fairly well with the experimental results. The model also explains many features of the spectrum observed in the experiments.

First observation of density profile in directly laser-driven polystyrene targets for ablative Rayleigh-Taylor instability research Reviewed

S Fujioka, H Shiraga, M Nishikino, K Shigemori, A Sunahara, M Nakai, H Azechi, K Nishihara, T Yamanaka

PHYSICS OF PLASMAS 10 ( 12 ) 4784 - 4789 2003.12

The temporal evolution of the density profile of a directly laser-driven polystyrene target was observed for the first time using an x-ray penumbral imaging technique coupled with side-on x-ray backlighting at the GEKKO XII [C. Yamanaka , IEEE J. Quantum Electron. QE-17, 1639 (1981)]-High Intensity Plasma Experimental Research laser facility (I-L=0.7x10(14) W/cm(2), lambda(L)=0.35 mum). This density measurement makes it possible to experimentally confirm all physical parameters [gamma(k),k,g,m,rho(a),L-m] appearing in the modified Takabe formula for the growth rate of the ablative Rayleigh-Taylor instability. The measured density profiles were well reproduced by a one-dimensional hydrodynamic simulation code. The density measurement contributes toward fully understanding the ablative Rayleigh-Taylor instability. (C) 2003 American Institute of Physics.

Equation-of-state measurements of polyimide at pressures up to 5.8 TPa using low-density foam with laser-driven shock waves Reviewed

K Takamatsu, N Ozaki, KA Tanaka, T Ono, K Nagai, M Nakai, T Watari, A Sunahara, M Nakano, T Kataoka, H Takenaka, M Yoshida, K Kondo, T Yamanaka

PHYSICAL REVIEW E 67 ( 5 ) 2003.5

The laser-driven equation-of-state (EOS) experiments for polyimide are presented. The experiments were performed with emission measurements from the rear sides of shocked targets at up to a laser intensity of 10(14) W/cm(2) or higher with 351 nm wavelength and 2.5 ns duration. Polyimide Hugoniot data were obtained up to 0.6 TPa with good accuracy. Applying low-density foam ablator to the EOS unknown material, we also obtained the data at a highest pressure of 5.8 TPa in the nonmetal materials. Those data were in agreement with the theoretical curves.

Side-on measurement of hydrodynamics of laser-driven plasmas with high space- and time-resolution x-ray imaging technique Reviewed

S Fujioka, H Shiraga, M Nishikino, Y Tamari, K Shigemori, M Nakai, H Azechi

REVIEW OF SCIENTIFIC INSTRUMENTS 74 ( 3 ) 2198 - 2201 2003.3

We developed and improved high space- and time-resolution x-ray imaging techniques (3-6 mum, 100-200 ps). These techniques were coupled with side-on x-ray backlighting for observing hydrodynamics of directly laser-driven polystyrene plasmas. As a high sensitive x-ray image detector, Imaging Plate was introduced to penumbral imaging technique [S. Fujioka et al, Rev. Sci. Instrum. 73, 2588 (2002)]. Noise in penumbral images was reduced by this improvement, and high quality density profiles of plasmas were obtained. A large-magnification slit camera, whose-slit width and magnification were 4 mum and 82.8, was coupled with an x-ray streak camera (XSC). Due to the advantage of the large-magnification, high spatial resolution of 5.8 mum was found even with an XSC, the photocathode of which usually has low spatial resolution. These techniques are useful in understanding of hydrodynamic instability in inertial confinement fusion. (C) 2003 American Institute of Physics.

Temporal evolution of temperature and density profiles of a laser compressed core (invited) Reviewed

Y Ochi, Golovkin, I, R Mancini, Uschmann, I, A Sunahara, H Nishimura, K Fujita, S Louis, M Nakai, H Shiraga, N Miyanaga, H Azechi, R Butzbach, E Forster, J Delettrez, J Koch, RW Lee, L Klein

REVIEW OF SCIENTIFIC INSTRUMENTS 74 ( 3 ) 1683 - 1687 2003.3

Temporal evolutions of the electron temperature and density profiles in the inertial confinement fusion core plasma were obtained through a combination of experimental technology to create a uniform core, diagnostics developments,,and a data analysis technique to obtain an optimal solution. In the experiment, time- and space-resolved x-ray spectroscopic measurements were carried out; an x-ray streak spectrograph and a monochromatic x-ray framing camera provided temporal evolution of x-ray spectrum and monochromatic emissivities, respectively. The spectrum and emissivity profile were iteratively fitted as a function of electron temperature, density, and space. Then, optimal solutions were successfully extracted with the help of Niched-Pareto genetic algorithm. Temporal behavior between those data is well corrected by comparing spatially and spectrally integrated intensities. The resultant profiles were compared with hydrocode simulations, showing that spatially averaged electron temperature and density evolutions are well replicated by the simulations, but their detail spatial profiles do not agree with them. (C) 2003 American Institute of Physics.

X-ray imaging diagnostics for laser-driven hydrodynamic instability experiments Reviewed

H Shiraga, H Azechi, M Nakai, K Shigemori, M Nishikino, T Sakaiya, S Fujioka, Y Tamari, T Yamanaka

REVIEW OF SCIENTIFIC INSTRUMENTS 74 ( 3 ) 2194 - 2197 2003.3

Rayleigh-Taylor (RT) instability is one of the most important physical issues in the inertial confinement fusion research. The reduction of its growth rate due to laser-driven ablation, which is described by the modified Takabe formula, is of great importance for-a precise understanding of the target physics. We have developed various diagnostic techniques for the measurement of the parameters appearing in the Takabe formula, such as the growth rate, the acceleration, the mass ablation rate, and the density structure including ablation density and density scalelength. Face-on and side-on x-ray backlighting were coupled with moire interferometry imaging, penumbral imaging, and Fresnel zoneplate imaging. All the physical parameters related to RT instability were measured experimentally, and compared with simulation results. (C) 2003 American Institute Of Physics.

Equation-of-state measurements of polyimide at pressures up to 5.8 TPa using low-density foam with laser-driven shock waves Reviewed

K. Takamatsu, N. Ozaki, K. A. Tanaka, T. Ono, K. Nagai, M. Nakai, T. Watari, A. Sunahara, M. Nakano, T. Kataoka, H. Takenaka, M. Yoshida, K. Kondo, T. Yamanaka

Physical Review E - Statistical Physics, Plasmas, Fluids, and Related Interdisciplinary Topics 67 ( 5 ) 5 2003

The laser-driven equation-of-state (EOS) experiments for polyimide are presented. The experiments were performed with emission measurements from the rear sides of shocked targets at up to a laser intensity of [Formula presented] or higher with 351 nm wavelength and 2.5 ns duration. Polyimide Hugoniot data were obtained up to 0.6 TPa with good accuracy. Applying low-density foam ablator to the EOS unknown material, we also obtained the data at a highest pressure of 5.8 TPa in the nonmetal materials. Those data were in agreement with the theoretical curves. © 2003 The American Physical Society.

High-speed x-ray radiographic measurement of laser-driven hydrodynamic instability Reviewed

H Shiraga, H Azechi, M Nakai, K Shigemori, M Nishikino, T Sakaiya, S Fujioka, Y Tamari, T Yamanaka

25TH INTERNATIONAL CONGRESS ON HIGH-SPEED PHOTOGRAPHY AND PHOTONICS 4948 425 - 430 2003

Hydrodynamic instability in laser-irradiated targets have been investigated in detail by using ultra high-speed x-ray radiographic technique. Recently developed high-resolution x-ray imaging for laser-driven Rayleigh-Taylor (RT) instability experiments as well as data including RT growth rate, ablation density and plasma density profile are described. Results are of great importance for comprehensive understanding of the dispersion relation of the laser-driven RT instability. Especially, direct observation of the ablation density was first achieved with temporal and spatial resolutions of 100 ps and 3 mum, respectively. Imaging technique includes x-ray Moire imaging, x-ray penumbral imaging and Fresnel phase zone plate imaging coupled with x-ray streak cameras or x-ray CCD cameras. Experiments were performed by using Gekko-XII/HIPER laser system at the Institute of Laser Engineering, Osaka University.

Hydrodynamic instability experiments on the HIPER laser Reviewed

K Shigemori, H Azechi, S Fujioka, Y Kanai, N Miyanaga, A Murakami, T Muranaka, H Nagatomo, M Nakai, M Nishikino, K Nishihara, H Nishimura, T Sakaiya, H Shiraga, A Sunahara, H Takabe, T Takayama, Y Tamari, A Tanaka, T Yamanaka

PLASMA PHYSICS 669 269 - 272 2003

We present recent results on the hydrodynamic instability experiments on the HIPER (High Intensity Plasma Experimental Research) laser facility at Institute of Laser Engineering, Osaka University. We measured the Rayleigh-Taylor growth rate on the HIPER laser. Also measured were all parameters that determine the RT growth rate. We focused on the measurements of the ablation density of laser-irradiated targets, which had not been experimentally measured. The experimental results were compared with calculations with one dimensional simulation coupled with and without Fokker-Planck equation for electron heat transport.

Progress in understanding of laser-produced plasmas for EUV source Reviewed

N Miyanaga, K Fujima, S Fujioka, Y Fujimoto, H Fujita, H Furukawa, K Hashimoto, T Hibino, T Kagawa, T Kato, T Kawamura, F Koike, R Matsui, R More, M Murakami, K Nagai, M Nakai, M Nakatsuka, T Nishikawa, K Nishihara, H Nishimura, T Norimatsu, T Okuno, A Sasaki, K Shigemori, Y Shimada, FL Sohnatzadeh, A Sunahara, H Tanuma, Y Tao, K Tsubakimoto, S Uchida, M Yamaura, H Yoshida, Zhakhovskii, V, Y Izawa

2003 IEEE LEOS ANNUAL MEETING CONFERENCE PROCEEDINGS, VOLS 1 AND 2 297 - 298 2003

Study on EUV emission properties of laser-produced plasma at ILE, Osaka Reviewed

M Nakai, H Nishimura, K Shigemori, N Miyanaga, T Norimatsu, K Nagai, R Matsui, T Hibino, T Okuno, FS Sohbatzadeh, Y Tao, K Hashimoto, M Yamaura, S Fujioka, H Nagatomo, Zhakhovckii, V, K Nishihra, S Uchida, Y Shimada, H Furukawa, M Nakatsuka, Y Izawa

LASER-GENERATED AND OTHER LABORATORY X-RAY AND EUV SOURCES, OPTICS, AND APPLICATIONS 5196 289 - 297 2003

A new research project on extreme ultraviolet (EUV) source development has just been started at the Institute of Laser Engineering, Osaka University. The main task of this project is to find a scientific basis for generating efficient, high-quality, high power EUV plasma source for semiconductor industry. A set of experimental data is to be provided to develop a detailed atomic model included in computer code through experiments using GEKKO-XII high power laser and smaller but high-repetitive lasers. Optimum conditions for efficient EUV generation will be investigated by changing properties of lasers and targets. As the,first step of the experiments, spherical solid tin and tin-oxide. targets were illuminated uniformly with twelve beams from the GEKKO XII. It has been confirmed that maximum conversion efficiency into 13.5 nm EUV light is achieved at illumination intensity less than 2 x 10(11) W/cm(2). No significant difference is found between laser wavelengths of one pm and a half mum. Density structure of the laser-irradiated surface of a planar tin target has been measured experimentally at 10(12) W/cm(2) to show formation of double ablation structure with density plateau by thermal radiation transport. An opacity experiment has just been initiated.

Nuclear fusion - Fast heating scalable to laser fusion ignition Reviewed

R Kodama, H Shiraga, K Shigemori, Y Toyama, S Fujioka, H Azechi, H Fujita, H Habara, T Hall, Y Izawa, T Jitsuno, Y Kitagawa, KM Krushelnick, KL Lancaster, K Mima, K Nagai, M Nakai, H Nishimura, T Norimatsu, PA Norreys, S Sakabe, KA Tanaka, A Youssef, M Zepf

NATURE 418 ( 6901 ) 933 - 934 2002.8

Penumbral imaging for measurement of the ablation density in laser-driven targets Reviewed

S Fujioka, H Shiraga, M Nishikino, M Heya, K Shigemori, M Nakai, H Azechi, S Nakai, T Yamanaka

REVIEW OF SCIENTIFIC INSTRUMENTS 73 ( 7 ) 2588 - 2596 2002.7

One-dimensional (1D) penumbral imaging technique with high spatial resolution has been developed, and applied to density profile measurements in laser-driven Rayleigh-Taylor instability experiments at a GEKKO XII-HIPER laser system. A laser-irradiated planar target was observed with side-on x-ray backlighting. A penumbral image of an x-ray radiograph was made by using a knife-edge imager. The x-ray radiograph was, then, reconstructed by differentiating the penumbral image with a proper Wiener filtering. A density profile was deduced from the reconstructed x-ray radiograph. In a proof-of-principle experiment, the density profile of a polystyrene (PS) target before laser irradiation was measured by using this method, and high spatial resolution of 3-4 mum was demonstrated. A laser-irradiated PS target in the acceleration phase was observed. The experimentally observed density profile was found to be consistent with the prediction by a 1D hydrodynamic simulation code. The x-ray penumbral imaging is a very simple and useful technique with high spatial resolution for research in hydrodynamics relevant to inertial fusion energy. (C) 2002 American Institute of Physics.

Single spatial mode experiments on initial laser imprint on direct-driven planar targets Reviewed

M Nakai, H Azechi, N Miyanaga, K Shigemori, T Kawasaki, T Nagaya, M Nishikino, Y Kanai, D Ohnuki, H Nishimura, H Shiraga, O Maegawa, R Ishizaki, K Nishihara, H Takabe, T Yamanaka

PHYSICS OF PLASMAS 9 ( 5 ) 1734 - 1744 2002.5

Flat plastic targets were directly irradiated and accelerated by partially coherent light from the GEKKO XII laser [Yamanaka , IEEE J. Quantum Electron. QE-17, 1639 (1981)] with the wavelength of 0.53 mum in order to investigate initial laser imprinting. The growth of the perturbation imprinted on the target by an initial foot pulse modulated with a single spatial frequency was observed by the face-on x-ray backlight technique. Imprint levels produced by the foot beam with a stationary intensity modulation of the illumination profile and with a dynamically changing modulation were successfully obtained by an image relay technique and the improved two-wavelength Young's interference method. Simple analytic models are proposed and compared with the experimental results. Stationary imprinting with perturbation wavelength longer than the target thickness is found to be well described by a simple incompressible model. The dynamic dependence of the imprint on the time scale of the temporal illumination profile is found to be qualitatively explained by linear perturbation analysis. (C) 2002 American Institute of Physics.

Imprint reduction in a plasma layer preformed with x-ray irradiation Reviewed

M Nishikino, H Shiraga, N Miyanaga, N Ohnishi, K Shigemori, S Fujioka, M Nakai, H Nishimura, H Azechi, K Mima, H Takabe, S Nakai, T Yamanaka

PHYSICS OF PLASMAS 9 ( 4 ) 1381 - 1391 2002.4

Indirect-direct-hybrid irradiation scheme has been proposed for suppressing the initial imprint of the laser irradiation nonuniformities. The target is irradiated by a low intensity x-ray radiation prior to the direct-drive laser pulse. The x-ray irradiation generates a plasma expansion layer on the target surface. The thermal smoothing effect is expected to take place in the preformed plasma when the direct-drive laser pulse comes onto the target, and then, the initial imprint can be significantly reduced. Planar target experiments on the indirect-direct-hybrid irradiation scheme were performed. The preformed plasma profile was measured by using x-ray side-on backlighting method. The reduction of the initial imprint was demonstrated by the indirect-direct-hybrid irradiation scheme on planar target experiments. The imprint is suppressed by a factor of 1.5-7 depending on x-ray preirradiation conditions. Results are in good agreement with the cloudy-day model with parameters derived from one-dimensional simulation. (C) 2002 American Institute of Physics.

Perturbation transfer from the front to rear surface of laser-irradiated targets Reviewed

K Shigemori, H Azechi, M Nakai, T Endo, T Nagaya, T Yamanaka

PHYSICAL REVIEW E 65 ( 4 ) 2002.4

We present experimental results on the perturbation transfer of laser irradiated planar foils. Perturbed polystyrene foils were irradiated directly by laser at intensity of 6x10(13) W/cm(2). We measured perturbations on the foils by side-on x-ray backlighting technique. Perturbations on the rear surface due to the rippled shock front were observed just after the shock breakout. We also observed feedthrough of perturbations on the laser-irradiated surface that grows due to the Rayleigh-Taylor instability.

Ablative Rayleigh-Taylor instability at short wavelengths observed with moire interferometry Reviewed

T Sakaiya, H Azechi, M Matsuoka, N Izumi, M Nakai, K Shigemori, H Shiraga, A Sunahara, H Takabe, T Yamanaka

PHYSICAL REVIEW LETTERS 88 ( 14 ) 2002.4

One of the most important quantities to be measured for better understanding of the ablative Rayleigh-Taylor (RT) instability is the growth rate in the short wavelength region at which the RT instability is significantly reduced. The short wavelength (4.7-12 mum) RT growth rates for direct-drive targets were measured for the first time by utilizing the innovated moire interferometry [M. Matsuoka et al., Rev. Sci. Instrum. 70, 637 (1999)]. These growth rates were reasonably well reproduced by the simulation that solves the Fokker-Planck equation for nonlocal heat transport.

Perturbation transfer from the front to rear surface of laser-irradiated targets Reviewed

K. Shigemori, H. Azechi, M. Nakai, T. Endo, T. Nagaya, T. Yamanaka

Physical Review E - Statistical, Nonlinear, and Soft Matter Physics 65 ( 4 ) 045401/4 2002.4

We present experimental results on the perturbation transfer of laser irradiated planar foils. Perturbed polystyrene foils were irradiated directly by laser at intensity of 6 × 1013 W/cm2. We measured perturbations on the foils by side-on x-ray backlighting technique. Perturbations on the rear surface due to the rippled shock front were observed just after the shock breakout. We also observed feedthrough of perturbations on the laser-irradiated surface that grows due to the Rayleigh-Taylor instability. © 2002 The American Physical Society.

Perturbation transfer from the front to rear surface of laser-irradiated targets Reviewed

K. Shigemori, H. Azechi, M. Nakai, T. Endo, T. Nagaya, T. Yamanaka

Physical Review E - Statistical Physics, Plasmas, Fluids, and Related Interdisciplinary Topics 65 ( 4 ) 4 2002

We present experimental results on the perturbation transfer of laser irradiated planar foils. Perturbed polystyrene foils were irradiated directly by laser at intensity of [formula presented] We measured perturbations on the foils by side-on x-ray backlighting technique. Perturbations on the rear surface due to the rippled shock front were observed just after the shock breakout. We also observed feedthrough of perturbations on the laser-irradiated surface that grows due to the Rayleigh-Taylor instability. © 2002 The American Physical Society.

Rayleigh Taylor and laser imprinting diagnostics Reviewed

H Azechi, M Nakai, K Shigemori, N Izumi, H Shiraga, M Nishikino, T Sakaiya, S Fujioka, Y Tamari, N Miyanaga, H Nishimura

ADVANCED DIAGNOSTICS FOR MAGNETIC AND INERTIAL FUSION 169 - 176 2002

Density profile of the ablating plasma produced by soft x-ray irradiation

M Nishikino, H Shiraga, M Matsuoka, S Fujioka, K Shigemori, M Nakai, H Azechi, N Miyanaga, T Yamanaka, S Nakai

REVIEW OF SCIENTIFIC INSTRUMENTS 72 ( 1 ) 653 - 656 2001.1

Indirect/direct-hybrid irradiation has been proposed for suppressing the initial imprint of laser-irradiation nonuniformities. Indirect soft x-ray preirradiation of the target generates a plasma expansion layer on the target surface. When the drive laser beam comes later, the target has a substantial stand-off distance between the ablation front and the beam absorption region, in which the thermal smoothing effect is expected to take place, and then, the initial imprint of the laser irradiation nonuniformities can be significantly reduced. Stand-off distance is of great importance in the imprint mitigation. We measured the preformed plasma profile by using the x-ray side-on backlighting method. The preformed plasma was backlit by x rays and imaged onto an x-ray streak camera. The scale length of the preformed plasma was found to increase with duration of the soft x-ray irradiation. The expansion velocity was found to be 6 x 10(5) cm/s at an x-ray irradiation of 1 x 10(11) W/cm(2). (C) 2001 American Institute of Physics.

Monochromatic x-ray imaging with bent crystals for laser fusion research

K Fujita, H Nishimura, Niki, I, J Funakura, Uschmann, I, R Butzbach, E Forster, M Nakai, M Fukao, A Sunahara, H Takabe, T Yamanaka

REVIEW OF SCIENTIFIC INSTRUMENTS 72 ( 1 ) 744 - 747 2001.1

Monochromatic x-ray imaging with toroidally bent crystals has been applied to investigate critical issues in laser fusion research in collaboration with Jena University [for example, I. Uschmann , Rev. Sci. Instrum. 66, 734 (1995)]. Described in this article is the study on x-ray diagnostics to provide simultaneously time, space, and spectral resolutions for the laser fusion experiments by the use of toroidally bent crystals. A monochromatic x-ray imager was developed, which consists of two sets of identical five bent crystals and a fast x-ray framing camera. The attained spatial resolution of 6 mum, time resolution of 34 ps, and spectral resolution of 10 eV are high enough to observe temporal evaluation and temperature distribution of the laser fusion hot core. In addition, a new x-ray imager with bent crystal was developed to investigate hydrodynamic instabilities occurring in laser-driven planer targets as one of the most critical issues in laser fusion research. The imager was so designed as to match the experiments using rather thick, massive targets irradiated under the same condition as in the high-gain experiments. Configuration and specifications of the imager are presented. (C) 2001 American Institute of Physics.

Time-resolved ten-channel monochromatic imaging of inertial confinement fusion plasmas

Ingo Uschmann, Kazuhiza Fujita, Izam Niki, Randolf Butzbach, Hiroaki Nishimura, Jiro Funakura, Mitsuo Nakai, Eckhart Förster, Kunioki Mima

Applied Optics 39 ( 31 ) 5865 - 5865 2000.11

Feed-out of rear surface perturbation due to rarefaction wave in laser-irradiated targets

K Shigemori, M Nakai, H Azechi, K Nishihara, R Ishizaki, T Nagaya, H Nagatomo, K Mima

PHYSICAL REVIEW LETTERS 84 ( 23 ) 5331 - 5334 2000.6

We report experimental results on hydrodynamic perturbation transfer from the rear to the front of laser-irradiated targets. Flat polystyrene foils with rear-surface perturbations were irradiated by partially coherent light. We observed phase inversion of the rear surface after the shock breakout at the rear surface. Perturbations on the laser-irradiated surface arose due to the rippled rarefaction wave. Experimental results were well reproduced by a simple model with unperturbed hydrodynamic quantities calculated From the one-dimensional simulation.

Indirect-direct hybrid target experiments with the GEKKO XII laser Reviewed

H Nishimura, H Shiraga, H Azechi, N Miyanaga, M Nakai, N Izumi, M Nishikino, M Heya, K Fujita, Y Ochi, K Shigemori, N Ohnishi, M Murakami, K Nishihara, R Ishizaki, H Takabe, K Nagai, T Norimatsu, M Nakatsuka, T Yamanaka, S Nakai, C Yamanaka, K Mima

NUCLEAR FUSION 40 ( 3Y ) 547 - 556 2000.3

A new fusion capsule drive scheme was investigated. The capsule is illuminated by a low intensity thermal X ray pulse prior to the main drive pulse. This leads to a noticeable suppression of initial imprinting by the drive beam because of thermal smoothing in the preformed plasma. Of the several types of indirect-direct hybrid target, the authors investigated the hybrid effect for two types. One is a foam hybrid, in which the fuel capsule has a low density foam layer attached directly on its surface and where pulsed radiation generated from a thin high Z layer on the foam propagates through the foam, creating a preformed plasma. The other is an external hybrid, in which the capsule is illuminated by external X ray radiation generated using different beams from the capsule drive beams. The hybrid effect was demonstrated for both types by imposing an initial imprint on a planar target with an intensity modulated beam, and subsequent non-uniformity growth due to Rayleigh-Taylor instability was observed by means of face-on backlighting. The observed suppression due to the presence of the preformed plasma is interpreted by a cloudy day model for both hybrids. Capsule implosion experiments have also been started. The overall implosion dynamics observed is replicated by 1-D hydrocode simulations. Preliminary results from the implosion experiments are presented.

Hydrodynamic model experiment of the collision of supernova 1987A with its circumstellar ring using high power laser Reviewed

YG Kang, H Nishimura, H Takabe, H Azechi, T Norimatsu, M Nakai, H Nagatomo, A Sunahara, K Fujita, M Nakatsuka, K Mima, HG Kim, HJ Kong

HIGH-POWER LASERS IN ENERGY ENGINEERING 3886 489 - 495 2000

Laboratory simulation of the ejecta-ring collision of Supernova 1987A has been performed by using a high power laser system. Pure hydrodynamic modeling was applied using the invariance of the Euler equations and the experiment was designed with one-dimensional hydrodynamic simulations. Three laser beams of lambda = 0.53 mu m, at the intensity I = 2 x 10(14) W/cm(2) irradiated a CH foil to generate a strong shock wave and subsequent dense plasma flow in a low density CHO foam including a solid sphere at its center. Shock wave propagation and plasma flow with vortex ring - like structures were observed with gated x-ray radiography. Overall hydrodynamic behaviors are consistent with one- and two-dimensional hydrodynamic simulations. The collision dynamics is dominated by a complicated interplay of reflected shock, diffracted shock, transmitted shock waves, and plasma flow behind the main shock passage.

Indirect/direct-hybrid drive implosion experiments with x-ray pre-irradiation Reviewed

M Nishikino, H Shiraga, N Miyanaga, H Nishimura, K Shigemori, M Heya, H Azechi, M Nakai, K Mima, H Takabe, S Nakai, T Yamanaka

HIGH-POWER LASERS IN ENERGY ENGINEERING 3886 465 - 472 2000

Indirect/direct-hybrid drive scheme to suppress the initial imprint of the laser irradiation nonuniformities has been proposed and investigated as a new drive scheme for inertial fusion. In direct drive inertial confinement fusion, initial imprinting of laser irradiation nonunifornity is considered to cause seeding of the perturbation on target surface in the very beginning of the irradiation which may be amplified by Rayleigh-Taylor instability in the acceleration phase of the implosion and be deleterious to efficient heating of the hot spark at the center of the compressed fuel core plasma. In indirect/direct-hybrid drive scheme, the target is first irradiated very uniformly with low-intensity soft x-ray prepulse(indirect drive) from external sources apart from the target. Indirect x-ray pre-irradiation of the surface causes a pre-expansion layer of the plasma before the irradiation of the direct drive laser beam. When the drive beam(direct drive) comes later, the target has a substantial stand-off distance between the ablation front and the beam absorption region. Thus the thermal smoothing effect is expected to occur in this transport layer, and then, the initial imprint can be significantly reduced. We have demonstrated planar target experiments on the indirect/direct hybrid scheme and observed reduction of the initial imprint. Implosion experiments the indirect/direct hybrid drive spherical capsules with external x-ray sources has been started. Overall implosion was performed successfully.

Direct measurement of laser irradiation uniformity of fusion pellets by the use of X-ray frame images Reviewed

H Honda, H Nishimura, M Nakai, N Miyanaga, K Tsubakimoto, H Shiraga, H Azechi, H Takabe, K Nishihara, S Nakai, K Mima

FUSION ENGINEERING AND DESIGN 44 137 - 140 1999.2

Time-resolved 2-dimensional (2D) X-ray images were taken to evaluate laser irradiation non-uniformity of fusion pellets. X-ray distributions corresponding to the drive laser geometry were obtained on the circumference of the image of a gold-coated surrogate target. The experimental results were analyzed to derive the irradiances by using an experimentally-determine d relation between the laser irradiation intensity and the X-ray intensity. The analyzed results were compared with a laser illumination calculation in which temporally varying laser beams were projected onto a target sphere. A reasonable agreement between the measurement and calculation has been obtained. (C) 1999 Elsevier Science S.A. All rights reserved.

Effects of non-local electron thermal transport on ablative Rayleigh-Taylor instability Reviewed

M Honda, K Mima, K Shigemori, M Nakai, H Azechi, A Nishiguchi

FUSION ENGINEERING AND DESIGN 44 205 - 208 1999.2

A two-dimensional full Fokker-Planck (FP) simulation code coupled with an ideal fluid equation has been constructed. This code was applied for the numerical simulation of the Rayleigh-Taylor (RT) instability on the directly driven ablation front. The simulation results show that an accelerated thin foil is preheated by the non-local electron heat transport, the ablation front density is depleted, and the linear growth rate of the RT instability is suppressed strongly. By investigating the mode structure in the simulation, it is found that the peak of the eigen mode shifts toward the corona region by the non-local heat conduction effects. This is the reason why the growth rate is reduced. (C) 1999 Elsevier Science S.A. All rights reserved.

Hydrodynamic perturbation growth in the start-up phase Reviewed

R Ishizaki, K Nishihara, JG Wouchuk, K Shigemori, M Nakai, H Azechi, K Mima

FUSION ENGINEERING AND DESIGN 44 199 - 203 1999.2

A simple analytical model is presented to study hydrodynamic perturbation growth in the start-up phase in laser fusion, namely propagation of a rippled shock driven by non-uniform laser ablation induced by initial target roughness or non-uniform laser irradiation. These perturbation growths are very important because they seed the Rayleigh-Taylor (RF) instability in the subsequent acceleration and stagnation phases. We investigate temporal evolutions of the shock front and the ablation surface. In the result, we have found that the shock front ripples oscillate and decay in both cases of uniform laser irradiation on a target with a rippled surface and non-uniform laser irradiation on a smooth target surface. On the other hand, we obtain that there is the asymptotic value of the ablation surface deformation in the former case and the asymptotic growth rate of the ablation surface ripple in the latter case. Approximate formulas expressing both temporal evolutions of the shock front and the ablation surface are obtained in the weak shock limit. These formulas are also applicable in a relatively strong shock. We also investigate the case of oscillating non-uniform laser irradiation with time. The oscillation frequency dependences of the shock front ripple and the growth rate of the ablation surface ripple are discussed. (C) 1999 Elsevier Science S.A. All rights reserved.

Rippled shock propagation and hydrodynamic perturbation growth in laser implosion Reviewed

R Ishizaki, K Nishihara, JG Wouchuk, K Shigemori, M Nakai, N Miyanaga, H Azechi, K Mima

JOURNAL OF MATERIALS PROCESSING TECHNOLOGY 85 ( 1-3 ) 34 - 38 1999.1

A simple analytical model is presented to study hydrodynamic perturbation growth in the start-up phase in laser fusion, namely propagation of a rippled shock driven by nonuniform laser ablation induced by initial target roughness or nonuniform laser irradiation. These perturbation growths are very important, because they seed the Rayleigh-Taylor instability in the subsequent acceleration and stagnation phases. We investigate temporal evolutions of the shock front and the ablation surface. As a result, we have found that the shock front ripples oscillate and decay in both the case of uniform laser irradiation on a target with a rippled surface and that of nonuniform laser irradiation on a smooth target. It was also found that there is an asymptotic value of the ablation surface deformation in the former case and an asymptotic growth rate of the ablation surface ripple in the latter case. Approximate formulae expressing both temporal evolutions of the shock front and the ablation surface are obtained in the weak shock limit. These formulae are also applicable in a relatively strong shock. We also investigate the case of oscillating nonuniform laser irradiation with time. The oscillation frequency dependences of the shock front ripple and the growth rate of the ablation surface ripple are discussed. (C) 1999 Elsevier Science S.A. All rights reserved.

Progress of direct drive laser fusion research at ILE, Osaka Reviewed

K Mima, H Azechi, H Fujita, N Izumi, T Jitsuno, Y Kato, T Kanabe, Y Kitagawa, R Kodama, N Miyanaga, M Nakai, M Nakatsuka, S Nakai, H Nagatomo, T Norimatsu, K Nishihara, H Nishimura, H Shiraga, H Takabe, T Yamanaka

THIRD INTERNATIONAL CONFERENCE ON SOLID STATE LASERS FOR APPLICATION TO INERTIAL CONFINEMENT FUSION, PTS 1 AND 2 3492 34 - 41 1999

Reviewed are the progress in direct drive implosion researches with Gekko XII laser system. Precise observation of the growth rate of Rayleigh-Taylor instability and the suppression of imprints using indirect-direct hybrid implosion have been investigated. Theoretical and experimental researches on the fast ignition scheme are also studied. Relativistic laser plasma interaction experiments with Peta-Watt Module and Gekko XII are also described. Finally, the future direction of the research including the development of solid state laser for fusion reactor is discussed.

Measurements of mass ablation rate of laser-irradiated target by the face-on x-ray backlighting technique

K Shigemori, H Azechi, M Nakai, K Mima

REVIEW OF SCIENTIFIC INSTRUMENTS 69 ( 11 ) 3942 - 3944 1998.11

We report a novel method to measure the value of mass ablation rate per unit surface (m(over dot))in laser-irradiated targets. The face-on x-ray backlighting technique was utilized for the measurement. Flat polystyrene foils were irradiated by the partially coherent light at the intensity of 0.7 or 1.4 x 10(14) W/cm(2). We observed the residual areal mass of the planar targets to deduce temporally resolved mass ablation rate. Observed mass ablation rates are well reproduced both by the steady-state ablation model and by one-dimensional simulation. (C) 1998 American Institute of Physics. [S0034-6748(98)02111-X].

Comment on "Measurements of Rayleigh-Taylor growth rate of planar targets irradiated directly by partially coherent light" - Reply Reviewed

K Shigemori, H Azechi, M Nakai, H Takabe, K Mima

PHYSICAL REVIEW LETTERS 80 ( 15 ) 3415 - 3415 1998.4

Recent progress on diagnostic developments for ICF research at IEE Osaka Reviewed

H Nishimura, H Azechi, M Nakai, N Miyanaga, H Shiraga, R Kodama, N Izumi, M Heya, H Honda, K Fujita, Y Ochi, H Takabe, T Yamanaka, Y Kato, K Mima

PLASMA PHYSICS REPORTS 24 ( 2 ) 114 - 122 1998.2

A variety of novel diagnostic instruments and methods have been developed for use in laser fusion research at the Institute of Laser Engineering (ILE), Osaka University. Our efforts are particularly concentrated on development of a diagnostic method capable of high spatial, temporal, and energy resolutions, which, at the same time, makes it possible to observe precisely implosion stability and hot spark formation at the center of compressed plasma. Present status of the X-ray and particle diagnostics development is overviewed.

Rippled Shock Propagation and Hydrodynamic Perturbation Growth in Laser Implosion

R. Ishizaki, K. Nishihara, J. G. Wouchuk, K. Shigemori, M. Nakai, N. Miyanaga, H. Azechi, K. Mima

Review of High Pressure Science and Technology/Koatsuryoku No Kagaku To Gijutsu 7 930 - 932 1998

A simple analytical model is presented to study hydrodynamic perturbation growths induced by nonuniform laser ablation in the start-up phase in laser fusion. Namely, propagation of a rippled shock and deformation of an ablation surface caused by nonuniform laser ablation are studied for cases of initial target roughness and nonuniform laser irradiation. The perturbation growth is very important because it seeds the Rayleigh-Taylor instability in the subsequent acceleration and stagnation phases. In result, it can be shown that high intensity of laser irradiation promotes the ablation surface to distort and short wavelength of laser inhibits its deformation. Those behaviors are also investigated in the case that nonuniformity of laser irradiation oscillates with time. © 1998, The Japan Society of High Pressure Science and Technology. All rights reserved.

Direct-drive hydrodynamic instability experiments on the GEKKO XII laser Reviewed

H Azechi, M Nakai, K Shigemori, N Miyanaga, H Shiraga, H Nishimura, M Honda, R Ishizaki, JG Wouchuk, H Takabe, K Nishihara, K Mima, A Nishiguchi, T Endo

PHYSICS OF PLASMAS 4 ( 11 ) 4079 - 4089 1997.11

Hydrodynamic instabilities, such as the Rayleigh-Taylor (R-T) instability, play a critical role in inertial confinement fusion as they finally cause fuel-pusher mixing that potentially quenches thermonuclear ignition. Good understanding of the instabilities is necessary to limit the mixing within a tolerable level. A series of experiments has been conducted on the GEKKO XII laser facility [C. Yamanaka et al., IEEE J. Quantum Electron. QE-17, 1639 (1981)] to measure hydrodynamic instabilities in planar foils directly irradiated by 0.53 mu m laser light. It has been found that (1) the imprint is reasonably explained by an imprint model based on the equation of motion with the pressure perturbation smoothed by the cloudy-day effect, and (2) the experimental R-T growth rate is significantly reduced from the classical growth rate due probably to ablative stabilization enhanced by nonlocal heat transport. (C) 1997 American Institute of Physics. [S1070-664X(97)0-2811-5].

Three-dimensional imaging of laser-imploded targets using X-ray computed tomography technique Reviewed

YW Chen, N Miyanaga, M Yamanaka, M Nakai, T Yamanaka, S Nakai

IEEE TRANSACTIONS ON NUCLEAR SCIENCE 44 ( 3 ) 890 - 893 1997.6

Irradiation uniformity measurement of laser fusion pellets by an X-ray imaging method Reviewed

H Honda, H Nishimura, S Miyamoto, M Nakai, K Kondo, N Miyanaga, K Tsubakimoto, H Azechi, S Nakai, K Mima

FUSION ENGINEERING AND DESIGN 34-35 197 - 200 1997.3

Time integrated X-ray emission images at an energy range of 1.8-3.6 keV were obtained to evaluate laser irradiation nonuniformity on fusion pellets. The experimental results were analyzed with a simple illumination calculation. A positive correlation was found between the nonuniformity obtained from the measured X-ray emission intensity and that from the calculated laser irradiation intensity, although the absolute values of the nonuniformities are discrepant. (C) 1997 Elsevier Science S.A.

Measurements of Rayleigh-Taylor growth rate of planar targets irradiated directly by partially coherent light

K Shigemori, H Azechi, M Nakai, M Honda, K Meguro, N Miyanaga, H Takabe, K Mima

PHYSICAL REVIEW LETTERS 78 ( 2 ) 250 - 253 1997.1

We report the first measurements of laser-driven Rayleigh-Taylor instability at the linear growth regime in an imprint-free condition. Initially rippled polystyrene foils were irradiated by the partially coherent light. We measured temporal evolution of areal-density perturbation by the face-on x-ray backlighting technique. The observed maximum growth factor was nearly 50. We also measured the acceleration of the irradiated foil. The growth rate was approximately 50% of the classical growth rate. These experimental results were well reproduced by a two-dimensional simulation coupled with the Fokker-Planck treatment of electron heat transport.

Study of laser-imploded core plasmas with an advanced Kirkpatrick-Baez x-ray microscope

R Kodama, H Shiraga, M Miyanaga, T Matsushita, M Nakai, H Azechi, K Mima, Y Kato

REVIEW OF SCIENTIFIC INSTRUMENTS 68 ( 1 ) 824 - 827 1997.1

We developed an advanced Kirkpatrick-Baez (AKB) x-ray microscope which consisted of two hyperbolic mirrors and two elliptic mirrors. The spatial resolution of less than or similar to 3 mu m was realized over similar to 1 mm diam. This AKB microscope was used for x-ray imaging in laser fusion experiments. Laser absorption nonuniformity with a large wave number on a spherical solid target or a plane slab target was estimated by measurements of x-ray emission from the target surface with the microscope. The x-ray images of the imploded core plasmas were also obtained with the AKB microscope, changing the laser focus condition and the laser energy balance. (C) 1997 American Institute of Physics.

Experimental study on laser irradiation nonuniformity caused by beam power imbalance Reviewed

H Honda, H Nishimura, S Miyamoto, M Nakai, K Kondo, N Miyanaga, K Tsubakimoto, H Shiraga, H Azechi, K Nishihara, K Mima

ICPP 96 CONTRIBUTED PAPERS - PROCEEDINGS OF THE 1996 INTERNATIONAL CONFERENCE ON PLASMA PHYSICS, VOLS 1 AND 2 1782 - 1785 1997

Time-resolved 2-dimensional (2D) x-ray images were obtained to evaluate laser irradiation nonuniformity on fusion pellets caused by laser beam power imbalance. Intensity modulation was observed on the circumference of the detected image corresponding to laser beam geometry. The experimental results were analyzed with an illumination calculation in which twelve laser beams are simply projected onto a solid sphere and the emitted x-ray flux is assumed to be proportional to the incident laser flux. At early time of laser irradiation, a good agreement between the measured x-ray emission intensity and the model prediction was obtained whereas small discrepancy was found in later time probably due to the omission of plasma expansion.

Hydrodynamic instability experiments at GEKKO XII Reviewed

H Azechi, M Nakai, K Shigemori, A Nishiguchi, N Miyanaga, M Honda, H Shiraga, R Kodama, O Maekawa, R Ishizaki, H Takabe, K Nishihara, Y Kato, T Yamanaka, S Nakai, K Mima, T Endo, C Yamanaka

FUSION ENERGY 1996, VOL 3 223 - 231 1997

Hydrodynamic instabilities play an important role in inertial confinement fusion implosions. Target surface perturbations will grow, primarily owing to the Rayleigh-Taylor (R-T) instability and finally resulting in fuel-pusher mixing that degrades the implosion performance. Good understanding of the instabilities is necessary to limit the mixing to a tolerable level. At the GEKKO XII laser facility, an extensive series of direct drive experiments has been conducted on the effect of rippled shock propagation, initial imprinting and its suppression by X ray pre-irradiation, and the R-T instability in the linear regime. As to the drive laser, partially coherent light achieves the state-of-the-art uniformity by which spurious imprints are minimized. For the initial imprinting experiments, a single mode perturbation was introduced on the foot pulse for imprint, followed by a uniform main pulse for R-T amplification. The experimental R-T growth rate was significantly reduced in comparison to the classical growth rare.

High-convergence uniform implosion of fusion pellets with the new GEKKO laser Reviewed

Nishimura H, Azechi H, Shiraga H, Nakai M, Miyanaga N, Takabe H, Norimastu T, Fujita H, Shigemori K, Heya M, Izumi S, Honda H, Fujita K, Sunahara A, Honda M, Kanabe T, Jitsuno T, Takagi M, Kodama R, Tanaka K.A, Nakatsuka M, Nishihara K, Kato Y, Yamanaka T, Nakai S, Mima K

Plasma Physics and Controlled Fusion 39 ( 5A ) 1997

Experiments on indirect/direct hybrid drive scheme Reviewed

H Shiraga, H Azechi, Y Kato, K Mima, N Miyanaga, M Murakami, M Nakai, S Nakai, K Nishihara, H Nishimura, T Norimatsu, K Shigemori, H Takabe, M Takagi, T Yamanaka, T Endo, C Yamanaka

FUSION ENERGY 1996, VOL 3 79 - 84 1997

Recent progress of laser fusion research with the GEKKO lasers at Ile, Osaka Reviewed

K Mima, M Nakatsuka, H Azechi, H Fujita, H Honda, M Honda, R Ishizaki, Y Izawa, N Izumi, T Jitsuno, T Kanabe, Y Kato, Y Kitagawa, R Kodama, S Matsuoka, N Miyanaga, M Murakami, M Nakai, S Nakai, K Nishihara, H Nishimura, T Norimatsu, S Sakabe, K Shigemori, H Shiraga, H Takabe, M Takagi, KA Tanaka, M Yamanaka, T Yamanaka, GY Yoon, A Nishiguchi, S Miyamoto, K Tsubakimoto, C Yamanaka

FUSION ENERGY 1996, VOL 3 13 - 30 1997

The irradiation symmetry of GEKKO XII has recently been improved. It is crucial for laser implosion to form a hot spark in a highly compressed cold fuel. Uniform laser irradiation was achieved by introducing Partially coherent light with angular spectral dispersion and by improving the power balance among the 12 beams. Implosion experiments with the improved GEKKO XII have been carried out to increase the neutron yield normalized by the 1-D simulation result. The normalized neutron yield is of order unity for a convergence ratio of less than 8. The improved uniformity also makes it possible to obtain experimental data which are necessary for the ignition target design. Namely, the Rayleigh-Taylor instability growth rate, the bandwidth dependence of the initial imprint, the effects of an X ray prepulse in reducing the initial imprint and so on have been investigated. As a new project directed towards ignition and burn, an ultra-intense short pulse laser beam is to be added to the GEKKO XII system. This short pulse laser is capable of delivering 100 J/l ps into the compressed core plasma for investigating the feasibility of the fast ignition concept. In future, it will be upgraded to 1 kJ/1 ps to heat plasmas imploded by GEKKO XII.

Theoretical studies on uniformity and stability in direct drive laser fusion Reviewed

K Nishihara, H Takabe, M Murakami, R Ishizaki, JG Wouchuk, M Honda, A Sunahara, S Hasegawa, Y Shimuta, Y Ueshima, H Azechi, H Shiraga, H Nishimura, N Miyanaga, M Nakai, K Shigemori, Y Fukuda, K Mima, A Nishiguchi, H Sakagami

FUSION ENERGY 1996, VOL 3 161 - 170 1997

Uniformity and stability issues are investigated for three phases of a laser implosion process: startup, acceleration and stagnation. Hydrodynamic perturbation growth in the startup phase seeds the Rayleigh-Taylor (RT) instability in the subsequent phases. An analytical model is developed to study the propagation of a rippled shock and the deformation of an ablation surface driven by non-uniform laser ablation. Agreement between theory and experiment is found in the propagation of the shock front ripple and also in areal mass density perturbation. A new instability of the uniform contact surface is found to be driven by the rippled shock. For both linear and non-linear cases, the growth rate depends on the phase of the oscillating shock wave at the time when the shock hits the contact surface. Exact analytical solutions of the linear growth rates for the Richtrryer-Meshkov instability are found for both reflected shock and reflected rare action cases. They agree well with recent experiments. Two dimensional (2-D) Fokker-Planck heat transport is introduced in a 2-D hydrodynamic code to study the RT instability at the ablation surface. Non-local heat transport is shown to play an important role in reducing the growth rate. 2-D simulations are also carried out to study the neutron yield reduction observed in the GEKKO XII laser implosion experiments. It is found that odd number non-uniformity is dominant in repelling the fuel from the centre and in reducing the neutron yield. A new type of self-similar solution, which determines the stagnation dynamics, is obtained, and the density gradient generated by the conduction is shown to reduce the RT growth.

Three-dimensional imaging of laser-imploded targets using x-ray computed tomography technique Reviewed

YW Chen, N Miyanaga, M Yamanaka, M Nakai, T Yamanaka, S Nakai

1996 IEEE NUCLEAR SCIENCE SYMPOSIUM - CONFERENCE RECORD, VOLS 1-3 283 - 286 1997

Laser fusion research at ILE Osaka University Reviewed

S Nakai, M Nakatsuka, H Fujita, N Miyanaga, T Jitsuno, T Kanabe, Y Izawa, T Norimatsu, M Takagi, T Yamanaka, Y Kato, H Azechi, H Nishimura, H Shiraga, M Nakai, KA Tanaka, R Kodama, H Takabe, K Nishihara, K Mima, Y Kitagawa, S Sakabe, M Yamanaka, Y Kosaki, C Yamanaka, T Sasaki, Y Mori, K Miyazaki, M Nishikawa, H Kan, T Hiruma, Y Soman, H Ito, JM Perlado, E Alonso, E Munoz, J Sanz

FUSION TECHNOLOGY 30 ( 3 ) 625 - 633 1996.12

Measurements of Absorption Distribution by Second Harmonic and X-Ray Images

Kazuo A. Tanaka, Tomoki Ohnishi, Atsunori Ozaki, Tomohiro Matsushita, Mikio Nakasuji, Hiroyuki Hashimoto, Ryosuke Kodama, Yasushi Oshikane, Mitsuo Nakai, Masahiro Tsukamoto, Shinji Matsuioka, Kouji Tubakimoto, Masakatsu Murakami, Yoshinori Simada, Hiroshi Azechi, Hiroyuki Nishimura, Noriaki Miyanaga, Hiroyuki Shiraga, Yoshiaki Kato, Kunioki Mima, Sadao Nakai

1996.7

Recent progress of implosion experiments with uniformity-improved GEKKO XII laser facility at the Institute of Laser Engineering, Osaka University Reviewed

K Mima, Y Kato, H Azechi, K Shigemori, H Takabe, N Miyanaga, T Kanabe, T Norimatsu, H Nishimura, H Shiraga, M Nakai, R Kodama, KA Tanaka, M Takagi, M Natatsuka, K Nishihara, T Yamanaka, S Nakai

PHYSICS OF PLASMAS 3 ( 5 ) 2077 - 2083 1996.5

The irradiation uniformity of the GEKKO XII laser [C. Yamanaka et al., IEEE J. Quantum Electron. QE-17 1639 (1981)] has been improved by using partially coherent light with angular spectral dispersion and by improving power balance among the beams. Implosion experiments with the uniformity-improved GEKKO XII have been carried out in order to demonstrate stable formation of the hot spark. The isentrope of the compressed pellet shell is controlled by adding a prepulse to enhance the ablative stabilization of the Rayleigh-Taylor instability. The implosion dynamics has been investigated by x-ray imaging and neutron diagnostics. The experimental results are compared with the mix model prediction based on the one-dimensional hydrodynamic simulation. The degradation of neutron yield is attributed to the low-mode asymmetry. Finally, recent results of planer target experiments on the ablative stabilization of the Rayleigh-Taylor instability are also presented. The observed linear growth rate was about 50% of the classical growth rate and was lower than that of the theoretical prediction, based on the Takabe formula combined with the one-dimensional simulation. (C) 1996 American Institute of Physics.

Development of XUV lasers at the RAL central laser facility Reviewed

MH Key, WJ Blyth, AE Dangor, P Dhez, A Djoui, L Dwivedi, M Holden, PB Holden, P Jaegle, CLS Lewis, AG McPhee, A Modena, M Nakai, D Neely, PA Norreys, AA Offenberger, GJ Pert, JA Ploues, SG Preston, SA Ramsden, SJ Rose, B Russ, CG Smith, A Sureau, GJ Tallents, F Walsh, JS Wark, YL You, J Zhang

OPTICAL AND QUANTUM ELECTRONICS 28 ( 3 ) 201 - 208 1996.3

Recent progress in the development of XUV lasers by research teams using high-power and ultrashort-pulse Nd:glass and KrF laser facilities at the Rutherford Appleton Laboratory is reviewed. Injector-amplifier operation and prepulse enhanced output of the Ge XXIII collisional laser driven by a kilojoule glass laser, enhanced gain in CVI recombination with picosecond CPA drive pulses from a glass laser, and optical field ionization and XUV harmonic generation with a KrF CPA laser are described.

High-order harmonics of 248.6-nm KrF laser from helium and neon ions

SG Preston, A Sanpera, M Zepf, WJ Blyth, CG Smith, JS Wark, MH Key, K Burnett, M Nakai, D Neely, AA Offenberger

PHYSICAL REVIEW A 53 ( 1 ) R31 - R34 1996.1

Development and application of ultra-bright laser and harmonic XUV sources Reviewed

MH Key, TW Barbee, JW Blyth, K Burnett, GF Cairns, AE Dangor, T Ditmire, A Djaoui, LB DaSilva, A Demir, A Dyson, AP Fews, EE Fill, P Gibbon, P Lee, S Healy, M Holden, DH Kalantar, NS Kim, CLS Lewis, Y Li, J Lin, P Loukakos, AG McPhee, Mercer, I, S Moustaizis, M Nakai, D Neely, P Norreys, AA Offenberger, GJ Pert, SG Preston, BA Remmington, A Sanpera, D Schlogl, CG Smith, R Smith, J Steingruber, GJ Tallents, F Walsh, JS Wark, J Warwick, E Wolfrum, M Zepf, J Zhang

X-RAY LASERS 1996 ( 151 ) 9 - 16 1996

Experimental work with high intensity lasers at the Rutherford Appleton Laboratory has led to the production of both XUV laser and XUV harmonic sources with extreme brightness. In particular an efficient XUV laser source has been developed based on collisionally excited neon -like Ge XXIII(J=0-1) at 19.6 nm using the high power glass laser Vulcan generating 75 ps pulses. With Vulcan operating in sub -ps CPA mode, extremely powerful and short wavelength XUV high harmonic sources have been obtained by irradiation of solid targets and recombinant laser action with high gain has been demonstrated with fibre targets. An ultra-bright Krypton-fluoride laser system, Sprite(recently upgraded to a new configuration Titania) has produced the shortest harmonic wavelength (6.7 nm) and has been used to assess the possibilities of optical field ionised recombinant laser action with gas jet targets. The Ge XUV laser has been successfully applied in fusion research for radiographic measurements of the effect of laser speckle on the hydrodynamic stability of laser accelerated thin foils. The present status of the work, the comparative performance of the XUV laser and harmonic sources and near-term future directions are reviewed.

Implosion experiments with uniformity-improved GEKKO XII: Overview

Y Kato, H Azechi, H Takabe, N Miyanaga, T Kanabe, T Norimatu, H Nishimura, H Shiraga, M Nakai, R Kodama, KA Tanaka, M Takagi, M Nakatsuka, K Nishihara, K Mima, T Yamanaka, S Nakai

LASER INTERACTION AND RELATED PLASMA PHENOMENA pp101-107 ( 369 ) 101 - 107 1996

rho Delta R measurement of imploded cryogenic foam target by DD-protons

Y Kitagawa, KA Tanaka, M Nakai, T Yamanaka, K Nishihara, H Azechi, N Miyanaga, T Norimatsu, T Kanabe, C Chen, A Richard, M Sato, H Furukawa, S Nakai

LASER INTERACTION AND RELATED PLASMA PHENOMENA pp.136-142 ( 369 ) 136 - 141 1996

Stimulated Raman scattering from two overlapped 527 nm laser beams Reviewed

M Tsukamoto, KA Tanaka, K Mima, R Kodama, M Kado, S Nakaji, A Nishiguchi, M Nakai, T Norimatsu, K Nishihara, T Yamanaka, S Nakai

LASER INTERACTION AND RELATED PLASMA PHENOMENA ( 369 ) 459 - 464 1996

DYNAMIC BEHAVIOR OF RIPPLED SHOCK-WAVES AND SUBSEQUENTLY INDUCED AREAL-DENSITY-PERTURBATION GROWTH IN LASER-IRRADIATED FOILS (VOL 74, PG 3608, 1995) Reviewed

T ENDO, K SHIGEMORI, H AZECHI, A NISHIGUCHI, K MIMA, M SATO, M NAKAI, S NAKAJI, N MIYANAGA, S MATSUOKA, A ANDO, KA TANAKA, S NAKAI

PHYSICAL REVIEW LETTERS 75 ( 15 ) 2908 - 2908 1995.10

Observation of Plasma Density Profile in Cylinder-Type X-Ray-Driven Fusion Target by GIR Method

Yasushi Oshikane, Masahiro Tsukamoto, Kazuo A. Tanaka, Shin-ichi Nakaji, Tomoki Ohnishi, Hiroyuki Hashimoto, Mitsuo Nakai, Hideaki Takabe, Kunioki Mima, Yoshiaki Kato, Sadao Nakai, Akio Nishiguchi, Osaka Institute of Technology

1995.10

AREAL DENSITY-MEASUREMENT OF IMPLODED CRYOGENIC TARGET BY ENERGY PEAK SHIFT OF DD-PRODUCED PROTONS

Y KITAGAWA, KA TANAKA, M NAKAI, T YAMANAKA, K NISHIHARA, H AZECHI, N MIYANAGA, T NORIMATSU, T KANABE, C CHEN, A RICHARD, M SATO, H FURUKAWA, S NAKAI

PHYSICAL REVIEW LETTERS 75 ( 17 ) 3130 - 3133 1995.10

DD-produced protons are used to measure the imploded fuel-shell areal density rho Delta R. Twelve green beams of the GEKKO XII laser directly imploded a cryogenic foam-shell target containing a liquid or solid D-2 fuel. The proton emission is detected through a dipole magnet on a CR-39 plate, whose energy shift from 3.02 MeV yielded the maximum rho Delta R of 10 mg/cm(2) or the density of 6 g/cm(3), in agreement with that from the secondary neutron method within a factor of 2. The proton energy spread is sensitive to the laser energy imbalance.

CRYOGENIC DEUTERIUM TARGET EXPERIMENTS WITH THE GEKKO-XII, GREEN LASER SYSTEM

KA TANAKA, T YAMANAKA, K NISHIHARA, T NORIMATSU, N MIYANAGA, H SHIRAGA, M NAKAI, Y KITAGAWA, R KODAMA, T KANABE, H AZECHI, M HEYA, T JITSUNO, M KADO, K MIMA, M NAKATSUKA, A NISHIGUCHI, H TAKABE, M TAKAGI, K TSUBAKIMOTO, M TSUKAMOTO, Y KATO, Y IZAWA, S NAKAI

PHYSICS OF PLASMAS 2 ( 6 ) 2495 - 2503 1995.6

DYNAMIC BEHAVIOR OF RIPPLED SHOCK-WAVES AND SUBSEQUENTLY INDUCED AREAL-DENSITY-PERTURBATION GROWTH IN LASER-IRRADIATED FOILS

T ENDO, K SHIGEMORI, H AZECHI, A NISHIGUCHI, K MIMA, M SATO, M NAKAI, S NAKAJI, N MIYANAGA, S MATSUOKA, A ANDO, KA TANAKA, S NAKAI

PHYSICAL REVIEW LETTERS 74 ( 18 ) 3608 - 3611 1995.5

STIMULATED RAMAN-SCATTERING FROM SYMMETRICALLY ILLUMINATED 2-LAYERED SPHERICAL TARGETS WITH 527-NM LASER LIGHT Reviewed

M TSUKAMOTO, KA TANAKA, K MIMA, M KADO, S MIYAMOTO, M NAKAI, T NORIMATSU, M TAKAGI, K NISHIHARA, T YAMANAKA, S NAKAI, A NISHIGUCHI

PHYSICS OF PLASMAS 2 ( 2 ) 486 - 492 1995.2

Erratum: Dynamic behavior of rippled shock waves and subsequently induced areal-density-perturbation growth in laser-irradiated foils (Physical Review Letters (1995) 75, 15) Reviewed

Endo T, Shigemori K, Azechi H, Nishiguchi A, Mima K, Sato M, Nakai M, Nakaji S, Miyanaga N, Matsuoka S, Ando A, Tanaka K.A, Nakai S

Physical Review Letters 75 ( 15 ) 1995

HIGH HARMONIC-GENERATION WITH A CPA KRF LASER Reviewed

M ZEPF, W BLYTH, MH KEY, M NAKAI, SG PRESTON, JS WARK

LASER INTERACTION WITH MATTER ( 140 ) 467 - 470 1995

High harmonics have been observed from a 0.8 TW, 350-fs KrF CPA laser focused to 8 x 10(17) W cm(-2) in gas jet targets. Estimates of the absolute conversion efficiencies have been made. The efficiency and relative strength of the harmonics was found to be largely independent of the position of the laser focus within the gas jet, and of the density, suggesting a coherence length limited by dephasing effects due to plasma electrons. The highest harmonics are attributed to ions rather than neutrals.

IMPLOSION EXPERIMENTS OF CRYOGENICALLY COOLED TARGETS Reviewed

T YAMANAKA, KA TANAKA, K NISHIHARA, T NORIMATSU, H SHIRAGA, Y KITAGAWA, N MIYANAGA, H AZECHI, H NISHIMURA, M NAKAI, R KODAMA, M HEYA, M TAKAGI, Y IZAWA, T KANABE, T JITSUNO, M NAKATSUKA, K MIMA, M MURAKAMI, S NAKAI, T ENDO, C YAMANAKA

LASER INTERACTION WITH MATTER ( 140 ) 25 - 28 1995

Cryogenically cooled deuterium targets with plastic ablator are imploded as well as plastic targets with deuterium gas at laser intensities of 4-5x10(14) W/cm(2) and 1-2x10(14) W/cm(2). The low intensity shots showed neutron yields normalized by 1-D simulation to be one tenth up to convergence ratio of 30, while those at the high intensity are one hundredth. The observed neutron yields and density radius product rho Rs are respectively 10(8) and 8 mg/cm(2) for cryogenic liquid targets. 2-D x-ray images obtained with a 10 ps temporal resolution camera reveal previously undiscovered information of imploding core plasmas.

Observation of Raman light in expanding plasmas from two-layered spherical targets irradiated with 527 nm laser

M. Tsukamoto, K. A. Tanaka, K. Mima, M. Kado, S. Miyamoto, M. Nakai, T. Norimatsu, M. Takagi, K. Nishihara, T. Yamanaka, S. Nakai

1994.10

RECENT PROGRESS IN LASER FUSION-RESEARCH AT OSAKA-UNIVERSITY - UNIFORMITY AND STABILITY ISSUES

K NISHIHARA, M MURAKAMI, H AZECHI, T JITSUNO, T KANABE, M KATAYAMA, N MIYANAGA, M NAKAI, M NAKATSUKA, K TSUBAKIMOTO, S NAKAI

PHYSICS OF PLASMAS 1 ( 5 ) 1653 - 1661 1994.5

Improvement of laser irradiation uniformity in the Gekko XII system [IEEE J. Quantum Electron. QE-17, 1639 (1981)], both single beam pattern and power balance, is discussed. Substantial reduction of laser absorption nonuniformity is obtained for spherical harmonic modes greater than 15 by introducing spectrally dispersed amplified spontaneous emission. No perturbation growth is observed in flat foils accelerated by spectrally dispersed amplified spontaneous emission. Dependences of laser absorption uniformity on beam pattern and power imbalance are investigated in detail. The design goal of the power imbalance in the precision Gekko XII system is 3% in peak to valley, and laser absorption nonuniformity is estimated to be a few percent. Growth of hydrodynamic instabilities is analyzed for high convergence ratio implosions in the precision Gekko XII system.

IMPLOSION OF D-2 TEMPERATURE-CONTROLLED CRYOGENIC FOAM TARGETS WITH PLASTIC ABLATORS

A RICHARD, KA TANAKA, K NISHIHARA, M NAKAI, M KATAYAMA, YO FUKUDA, T KANABE, Y KITAGAWA, T NORIMATSU, M NAKATSUKA, T YAMANAKA, M KADO, T KAWASHIMA, C CHEN, M TSUKAMOTO, S NAKAI

PHYSICAL REVIEW E 49 ( 2 ) 1520 - 1526 1994.2

The implosion hydrodynamics of temperature-controlled cryogenic deuterium foam targets with plastic ablators is investigated. The experimental data recorded with x-ray imaging systems are compared to a one-dimensional (1D) simulation. The ablation front trajectories derived from x-ray streak-camera data agree with 1D simulation. However, an x-ray core emission is observed at an earlier time, and for a longer duration than that predicted. For the three liquid-fuel shots, the convergence ratios are, respectively, 0.4, 0.9, and 0.7 times that predicted by the ID simulation.

4.8-KEV X-RAY BACKLIGHT FRAMING METHOD FOR OBSERVING IMAGES OF SOFT-X-RAY-DRIVEN FUSION CAPSULES

M KATAYAMA, H SHIRAGA, M NAKAI, T KOBAYASHI, Y KATO

REVIEW OF SCIENTIFIC INSTRUMENTS 64 ( 3 ) 706 - 710 1993.3

We report on a diagnostic method for observing the implosion asymmetry of soft-x-ray-driven fusion capsules. The method consists of an x-ray backlight source using a 4.8-keV quasi-monochromatic titanium x-ray source and a fast multiframe x-ray imaging system. With the proper combination of spectral filters and photocathode to reduce intense background x rays from a gold cavity plasma, x-ray backlighting images of the fusion capsules have been successively obtained with spatial and temporal resolutions of 20 mum and 80 ps, respectively. These images are used to study the implosion velocity and the lower-mode distortion caused by x-ray irradiation nonuniformity on the imploding fusion capsule.

IMPLOSION EXPERIMENTS INVOLVING CRYOGENIC FOAM TARGETS WITH PLASTIC ABLATOR

T YAMANAKA, K NISHIHARA, KA TANAKA, T NORIMATSU, Y KITAGAWA, M NAKAI, M TAKAGI, A RICHARD, M KATAYAMA, C CHEN, M KADO, M TSUKAMOTO, T JITSUNO, R KODAMA, H AZECHI, N MIYANAGA, K MIMA, M NAKATSUKA, S NAKAI, T KANABE, M MURAKAMI, A NISHIGUCHI, C YAMANAKA

PLASMA PHYSICS AND CONTROLLED NUCLEAR FUSION RESEARCH 1992, VOL 3 pp 151-158 151 - 158 1993

PHYSICS HIGHLIGHTS OF THE GEKKO12-PROGRAM Reviewed

K MIMA, S NAKAI, H AZECHI, A NISHIGUCHI, H TAKABE, N MIYANAGA, H NAKANO, M NAKAI, M KATAYAMA, K NISHIHARA, N NAKATSUKA, T JITSUNO, K TANAKA, H NISHIMURA, H SHIRAGA, T ENDO, T YAMANAKA, Y KATO, C YAMANAKA

PLASMA PHYSICS AND CONTROLLED FUSION 34 ( 13 ) 1775 - 1783 1992.12

Recently, hollow shell pellets have been imploded uniformly by the Gekko 1 2 laser system to be compressed to several hundreds g/cm3. The compressed density has been measured both by the neutron activation methods and the electron degeneracy measurement. The densities given by the above two methods are consistent.
The target parameter dependences of the density are analyzed with die one climensional implosion simulation code. Except the case of high convergence ratio implosion, the compressed plasma density obtained by the simulation code with nonlocal heat transport and/or high energy electron preheating agrees with the experimental results. As for the high convergence implosion, the one dimensional simulation does not give good prediction of the implosion, in particular for the neutron yield. Actually, the experimental neutron yield for the convergence ratio higher than 20 is lower by more than two orders of magnitude than the simulation value.
The preheating and stability are the key physics for die high density compression. As for the preheating, it turns out that the two plasmon decay plays an important role in the accelerated shell preheating. As for the stability, the initial target surface roughness and the laser irradiation non-uniformity are carefully checked. By the theoretical stability analysis, the stability of the high density compression is found to be marginal. Therefore, we are afraid that the neutron yield may degradate by the hot-cold plasma mixing. The details of the Rayleigh-Taylor instability analysis and experiments are discussed in the text.

Generation of Stimulated Raman Scattering from Two-layerd Spherical Target Excited by 527nm-laser

TSUKAMOTO Masahiro

68 91 - 101 1992.11

COMPRESSION EXPERIMENTS AND PROSPECTS OF THERMONUCLEAR REACTION IGNITION ON GEKKO-XII INSTALLATION UNDER LTF PROGRAM Reviewed

S NAKAI, K MIMA, K AZECHI, N MIYANAGA, A NISHIGUCHI, T YAMANAKA, K NISHIKHARA, KA TANAKA, M NAKAI, R KODAMA, M KATAYAMA, M KADO, M TSUKOMOTO, KATO, I, K NISHIMURA, K SHIRAGA, T ENDO, M NAKATSUKA, T SASAKI, T YUTSUNO, K IOSHIDA, T KANABE, K NAKANO, M YAMANAKA, K NAITO, T NORIMATSU, M TAKAGI, T CHEN, Y IZAVA, S YAMANAKA

KVANTOVAYA ELEKTRONIKA 19 ( 10 ) 947 - 974 1992.10

Experimental results on high density compression of thermonuclear fuel on Gekko-XII installation are reported. The density of the compressed matter is up to 600 times high than the solid state density, rhoR parameter being 0.51 +/- 0.14 g/cm2. Prospects of going from the compression experiments to thermonuclear reaction ignition and high gain are studied numerically. A deeper insight into the processes occurring in the target cavity with indirect compression has been gained.

LASER FUSION - HIGH-DENSITY COMPRESSION EXPERIMENT AND IGNITION PROGRAM WITH GEKKO-XII Reviewed

S NAKAI, K MIMA, H AZECHI, N MIYANAGA, A NISHIGUCHI, T YAMANAKA, K NISHIHARA, KA TANAKA, M NAKAI, R KODAMA, M KATAYAMA, M KADO, M TSUKAMOTO, Y KATO, H TAKABE, H NISHIMURA, H SHIRAGA, T ENDO, M NAKATSUKA, T SASAKI, T JITSUNO, K YOSHIDA, T KANABE, H NAKANO, K TSUBAKIMOTO, M YAMANAKA, K NAITO, T NORIMATSU, M TAKAGI, T CHEN, Y IZAWA, C YAMANAKA

LASER INTERACTION AND RELATED PLASMA PHENOMENA, VOL 10 10 443 - 502 1992

TIME-RESOLVED MEASUREMENTS OF LASER-INDUCED SHOCK-WAVES IN DEUTERATED POLYSTYRENE POROUS TARGETS BY X-RAY BACKLIGHTING

R KODAMA, KA TANAKA, M NAKAI, K NISHIHARA, T NORIMATSU, T YAMANAKA, S NAKAI

PHYSICS OF FLUIDS B-PLASMA PHYSICS 3 ( 3 ) 735 - 744 1991.3

Experimental studies are presented of laser-driven shock waves in deuterated polystyrene porous targets observed with x-ray streak shadowgraphy. Using two different target-mass densities of 0.1 g/cm3 and 0.2 g/cm3, the density dependence of the shock velocity was obtained as upsilon-s proportional-rho-0.45 +/- 0.02 and agreed well with a simple scaling obtained from the Hugoniot relation. X-ray shadowgraphy has shown a shock formation in porous targets and analysis suggests that there are two parts to compression waves: a shock front and a following pileup zone of multiple shock waves. Temporal histories of the pressure, the temperature, and the compression were estimated from the measured shock velocities and the opacities. It was found that the pressure peak due to the shock front was retarded to that by the pileup zone. The pileup zone had a higher compression and followed a thermodynamic condition closer to an adiabat than the shock front.

MULTIFRAME X-RAY-IMAGING SYSTEM FOR TEMPORALLY AND SPATIALLY RESOLVED MEASUREMENTS OF IMPLODING INERTIAL CONFINEMENT FUSION-TARGETS

M KATAYAMA, M NAKAI, T YAMANAKA, Y IZAWA, S NAKAI

REVIEW OF SCIENTIFIC INSTRUMENTS 62 ( 1 ) 124 - 129 1991.1

A compact and simple multiframe x-ray imaging system was developed in order to monitor the implosion of spherical targets in inertial confinement fusion research. Time intervals between consecutive frames can be adjusted flexibly, and the maximum number of adjacent frames is 20 for an overall duration of 1.4 ns. Each frame is recorded with a temporal resolution of 83 +/- 20 ps, a spatial resolution of 10 lp/mm at a modulation transfer function of 20%, and an intensity dynamic range of 10(3). A proximity focused image intensifier with two microchannel plates allows to obtain a gain of 10(5). Measured temporal response and gain characteristics could be reproduced by a simple Monte Carlo calculation.

ANNEALING OF POLYSTYRENE MICROCAPSULES FOR INERTIAL CONFINEMENT FUSION EXPERIMENTS Reviewed

S KOBAYASHI, T NORIMATSU, M NAKAI, KA TANAKA, T YAMANAKA, S NAKAI, K ITO

JOURNAL OF VACUUM SCIENCE & TECHNOLOGY A-VACUUM SURFACES AND FILMS 9 ( 1 ) 150 - 153 1991.1

HIGH-DENSITY COMPRESSION EXPERIMENTS AT ILE, OSAKA Reviewed

H AZECHI, T JITSUNO, T KANABE, M KATAYAMA, K MIMA, N MIYANAGA, M NAKAI, S NAKAI, H NAKAISHI, M NAKATSUKA, A NISHIGUCHI, PA NORRAYS, Y SETSUHARA, M TAKAGI, M YAMANAKA

LASER AND PARTICLE BEAMS 9 ( 2 ) 193 - 207 1991

Direct-drive implosion experiments on the GEKKO XII laser (9 kJ, 0.5-mu-m, 2 ns) with deuterium and tritium (DT) exchanged plastic hollow shell targets demonstrated fuel areal densities (rho-R) of approximately 0.1 g/cm2 and fuel densities of approximately 600 times liquid density at fuel temperatures of approximately 0.3 keV. (The density and rho-R values refer only to DT and do not include carbons in the plastic targets.) These values are to be compared with thermonuclear ignition conditions, i.e. fuel densities of 500-1000 times liquid density, fuel areal densities greater than 0.3 g/cm2, and fuel temperatures greater than 5 keV. The irradiation nonuniformity in these experiments was significantly reduced to a level of < 5% in root mean square by introducing random-phase plates. The target irregularity was controlled to a 1% level. The fuel rho-R was directly measured with the neutron activation of Si, which was originally compounded in the plastic targets. The fuel densities were estimated from the rho-R values using the mass conservation relation, where the ablated mass was separately measured using the time-dependent X-ray emission from multilayer targets. Although the observed densities were in agreement with one-dimensional calculation results with convergence ratios of 25-30, the observed neutron yields were significantly lower than those of the calculations. This suggests the implosion uniformity is not sufficient to create a hot spark in which most neutrons should be generated.

HIGH-DENSITY COMPRESSION OF HOLLOW-SHELL TARGET BY GEKKO XII AND LASER FUSION-RESEARCH AT ILE, OSAKA-UNIVERSITY Reviewed

S NAKAI, K MIMA, M YAMANAKA, H AZECHI, N MIYANAGA, A NISHIGUCHI, H NAKAISHI, YW CHEN, Y SETSUHARA, PA NORREYS, T YAMANAKA, K NISHIHARA, KA TANAKA, M NAKAI, R KODAMA, M KATAYAMA, Y KATO, H TAKABE, H NISHIMURA, H SHIRAGA, T ENDO, K KONDO, M NAKATSUKA, T SASAKI, T JITSUNO, K YOSHIDA, T KANABE, A YOKOTANI, T NORIMATSU, M TAKAGI, H KATAYAMA, Y IZAWA, C YAMANAKA

LASER INTERACTION AND RELATED PLASMA PHENOMENA, VOL 9 9 25 - 67 1991

DEVELOPMENT OF X-RAY-EMISSION COMPUTED-TOMOGRAPHY FOR ICF RESEARCH

M NAKAI, S SHINOHARA, M KATAYAMA, YW CHEN, S KOBAYASHI, N MIYANAGA, KA TANAKA, K NISHIHARA, M YAMANAKA, T YAMANAKA, S NAKAI

REVIEW OF SCIENTIFIC INSTRUMENTS 61 ( 10 ) 2783 - 2785 1990.10

X-RAY AND PARTICLE DIAGNOSTICS OF A HIGH-DENSITY PLASMA BY LASER IMPLOSION

M NAKAI, M YAMANAKA, H AZECHI, YW CHEN, T JITSUNO, M KATAYAMA, M MIMA, N MIYANAGA, H NAKAISHI, M NAKATSUKA, A NISHIGUCHI, PA NORREYS, Y SETSUHARA, M TAKAGI, T NORIMATSU, T YAMANAKA, C YAMANAKA, S NAKAI

REVIEW OF SCIENTIFIC INSTRUMENTS 61 ( 10 ) 3235 - 3240 1990.10

3-DIMENSIONAL IMAGING OF LASER IMPLODED TARGETS Reviewed

YW CHEN, N MIYANAGA, M YAMANAKA, M NAKAI, K TANAKA, K NISHIHARA, T YAMANAKA, S NAKAI

JOURNAL OF APPLIED PHYSICS 68 ( 4 ) 1483 - 1488 1990.8

Three-dimensional imaging of laser imploded targets

Y.-W.Chen, N.Miyanaga, M.Yamanaka, M.Nakai, K.A.Tanaka, K.Nishihara, T.Yamanaka, S.Nakai

J. Appl. Phys. Vol.68 pp.1483-1488[SCI] 1990.8

3a-T-7 X-Ray Driven Fusion-III : Core Parameters

Endo T., Shiraga H., Nishimura H., Takabe H., Sakabe S., Kato Y., Nakai S., GOD-group, M-group, T-group, OT-group

Meeting Abstracts of the Physical Society of Japan 1990.4 190 1990

Three-Dimensional Temperature Distribution Measurement of Laser Imploded Core Plasma by use of X-Ray Emission Computed Tomography

NAKAI Mitsuo, SHINOHARA Seiichi, KATAYAMA Makoto, CHIN Yen-Uei, MIYANAGA Noriaki, TANAKA Kazuo, YAMANAKA Nasanobu, NISHIHARA Katsunobu, YAMANAKA Tasuhiko, NAKAI Sadao

ITE Technical Report 14 ( 31 ) 53 - 57 1990

A monitoring system for the real-time characterization of cryogenic fuel layer in laser-fusion targets.

TSUKAMOTO Masahiro, NAKAI Sadao, KODAMA Ryosuke, KADO Masataka, ITO Hajime, YASUMOTO Masaki, NORIMATSU Takayoshi, NAKAI Mitsuo, TANAKA Kazuo A, YAMANAKA Tatsuhiko

The Review of Laser Engineering 18 ( 9 ) 724 - 731 1990

We have developed a monitoring system for the real-time characterization of cryogenic fuel layer in laser-fusion targets. This system is composed of an imaging interferometer, in addition to a normal target postion monitor with a single optical path. The fabrication process of a solid fuel layer in a plastic spherical shell is observed with this system. Solid fuel layer uniformity is displayed as concentric interference patterns. The distortions of the interference patterns can be interpreted as fuel layer nonuniformities.

X-ray Pinhole Camera with Fluorescent Screen Coupled with CCD

Tanaka Kazuo, Shinohara Seiichi, Nakai Mitsuo, Yamanaka Tatsuhiko, Nakai Sadao

ITE Technical Report 13 ( 29 ) 1 - 4 1989

X-RAY FRAMING CAMERA IMAGES OF IMPLODING TARGETS Reviewed

M KATAYAMA, KA TANAKA, T YAMANAKA, Y IZAWA, S NAKAI, M NAKAI, C YAMANAKA

X-RAY INSTRUMENTATION IN MEDICINE AND BIOLOGY, PLASMA PHYSICS, ASTROPHYSICS, AND SYNCHROTRON RADIATION 1140 406 - 410 1989

FABRICATION OF A CRYOGENIC FOAM TARGET FOR INERTIAL CONFINEMENT FUSION EXPERIMENTS

T NORIMATSU, H KATAYAMA, T MANO, M TAKAGI, R KODAMA, KA TANAKA, Y KATO, T YAMANAKA, S NAKAI, Y NISHINO, M NAKAI, C YAMANAKA

JOURNAL OF VACUUM SCIENCE & TECHNOLOGY A-VACUUM SURFACES AND FILMS 6 ( 6 ) 3144 - 3147 1988.11

HYDRODYNAMIC INSTABILITY IN AN ABLATIVELY IMPLODED TARGET IRRADIATED BY HIGH-POWER GREEN LASERS Reviewed

H NISHIMURA, H TAKABE, K MIMA, F HATTORI, H HASEGAWA, H AZECHI, M NAKAI, K KONDO, T NORIMATSU, Y IZAWA, C YAMANAKA, S NAKAI

PHYSICS OF FLUIDS 31 ( 10 ) 2875 - 2883 1988.10

SCALINGS OF IMPLOSION EXPERIMENTS FOR HIGH NEUTRON YIELD Reviewed

TAKABE H, YAMANAKA M, MIMA K, YAMANAKA C, AZECHI H, MIYANAGA N, NAKATSUKA M, JITSUNO T, NORIMATSU T, TAKAGI M, NISHIMURA H, NAKAI M, YABE T, SASAKI T, YOSHIDA K, NISHIHARA K, KATO Y, IZAWA Y, YAMANAKA T, NAKAI S

Physics of Fluids 31 ( 10 ) 2884 - 2893 1988

DEVELOPMENT OF SUPRA-HIGHT SPEED X-RAY FRAMING CAMERA

KATAYAMA Makoto, NAKAI Mitsuo, NISHIMURA Hiroaki, YAMANAKA Tatsuhiko, IZAWA Yasukazu, NAKAI Sadao, YAMANAKA Chiyoe

ITE Technical Report 12 ( 22 ) 27 - 34 1988

We report on the construction and testing of a supra-high speed xray framing camera based on a gated microchannel plate. An infinite ground plane microstrip transmission-line configration is used. We used an InP optoelectric switch built into the microstrip transmission-line to generate the fast gating pulse. We have measured time and space resolution of the framing camera to. be better than 180psec and 15LP/mm. And coupling the camera with wolter type xray microscope, the xray images of a laser heated Au plasma were observed with 250psec intereframe time.

X-Ray Emission Computed Tomography of Laser-Produced Plasma

CHEN Ven-Wei, NISHIHARA Katsunobu, SHIMA Kyoko, MIYANAGA Noriaki, AZECHI Hiroshi, NAKAI Mitsuo, TANAKA Kazuo, YAMANAKA Masanobu, YAMANAKA Tatsuhiko, NAKAI Sadao, TAMURA Shinichi

ITE Technical Report 12 ( 22 ) 15 - 20 1988

STIMULATED RAMAN-SCATTERING IN CANNONBALL TARGETS Reviewed

Y SAKAWA, KA TANAKA, H NISHIMURA, M NAKAI, T YABE, H SAKURAI, Y IZAWA, Y KATO, T MOCHIZUKI, M NAKATSUKA, C YAMANAKA

PHYSICS OF FLUIDS 30 ( 10 ) 3276 - 3282 1987.10

OBSERVATION OF HYDRODYNAMIC INSTABILITY IN SPHERICAL TARGET IMPLOSION WITH A GEKKO-XII GREEN LASER Reviewed

NISHIMURA, H, IZAWA, Y, TAKABE, H, MIMA, K, NAKAI, M, UCHIDA, S, HASEGAWA, H, NORIMATSU, T, NAKAI, S, NAKATSUKA, H, JITSUNO, T, SAKABE, S, YAMANAKA, C

JOURNAL OF THE OPTICAL SOCIETY OF AMERICA B-OPTICAL PHYSICS 3 ( 8 ) P166-P167 1986.8

SUPRATHERMAL ELECTRON GENERATION IN CANNONBALL TARGETS Reviewed

H NISHIMURA, H AZECHI, M NAKAI, S UCHIDA, Y SAKAWA, T WADA, H HASEGAWA, H SAKURAI, T YAMANAKA, C YAMANAKA

OPTICS COMMUNICATIONS 56 ( 6 ) 409 - 414 1986.1

LASER IMPLOSION OF HIGH ASPECT-RATIO TARGETS PRODUCES THERMONUCLEAR NEUTRON YIELDS EXCEEDING 10(12) BY USE OF SHOCK MULTIPLEXING Reviewed

YAMANAKA C, NAKAI S, YABE T, NISHIMURA H, UCHIDA S, IZAWA Y, NORIMATSU T, MIYANAGA N, AZECHI H, NAKAI M, TAKABE H, JITSUNO J, MIMA K, NAKATSUKA M, SASAKI T, YAMANAKA M, KATO Y, MOCHIZUKI T, KITAGAWA Y, YAMANAKA T, YOSHIDA K

Physical Review Letters 56 ( 15 ) 1575 - 1578 1986

Laser Fusion Implosion Experiments

IZAWA Yasukazu, MIYANAGA Noriaki, NIKI Hideaki, TANAKA Kazuo A, MOCHIZUKI Takayasu, KITAGAWA Yoneyoshi, NAKAI Mitsuo, SHIRAGA Hiroyuki, YAMANAKA Masanobu, YAMANAKA Tatsuhiko, AZECH Hiroshi

The Review of Laser Engineering 14 ( 12 ) 1090 - 1132 1986

MEASUREMENTS OF INTENSITY SCALING OF ABLATION PRESSURE AT 10.6 MU-M AND 1.05 MU-M LASER WAVELENGTHS Reviewed

H DAIDO, R TATEYAMA, K OGURA, H AZECHI, M NAKAI, T YAMANAKA, K MIMA, S NAKAI, C YAMANAKA

JAPANESE JOURNAL OF APPLIED PHYSICS PART 1-REGULAR PAPERS SHORT NOTES & REVIEW PAPERS 23 ( 10 ) 1353 - 1356 1984

LASER WAVELENGTH AND INTENSITY SCALING OF ABLATION PRESSURE FOR LASER FUSION TARGETS. Reviewed

Hiroyuki Daido, Ryuji Tateyama, Kazuki Ogura, Hiroshi Azechi, Mitsuo Nakai, Tatsuhiko Yamanaka, Kunioki Mima, Sadao Nakai, Chiyoe Yamanaka

Technology Reports of the Osaka University 33 ( 1684-1702 ) 89 - 95 1983.3

Laser fusion Reviewed

J. H. Nuckolls, A. M. Prokhorov, S. Singer, R. L. McCrory, C. Yamanaka, S. Nakai, T. Yamanaka, Y. Kato, T. Mochizuki, A. F. Gibson, H. Azechi, M. Nakai, T. Yabe, H. Shiraga, F. Mizutani

Applied Physics B Photophysics and Laser Chemistry 28 ( 2-3 ) 269 - 273 1982.6

INTENSITY DEPENDENCE OF CLASSICAL AND COLLECTIVE ABSORPTION PROCESSES IN LASER-PRODUCED PLASMAS AT 1.053-MU-M AND 0.527-MU-M Reviewed

HAMA H, MIMA K, KATO Y, UENOYAMA T, MIYANAGA N, NAKAI M, YAMANAKA C

Ieee Transactions on Plasma Science 10 ( 1 ) 55 - 58 1982

A COMPARISON OF ABLATIVE ACCELERATION MEASUREMENTS Reviewed

A RAVEN, H AZECHI, M NAKAI, T MATSUO, T YAMANAKA, C YAMANAKA

APPLIED PHYSICS LETTERS 40 ( 9 ) 776 - 778 1982

　 PREV - NEXT 　

<Nakai Mitsuo>

Papers - Nakai Mitsuo