Faculty Profiles - Nakai Mitsuo

Papers - Nakai Mitsuo

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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 × 10<sup>8</sup> 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.

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Papers - Nakai Mitsuo