研究者詳細 - 中井　光男

論文 - 中井　光男

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Towards realization of hyper-velocities for impact fast ignition 査読

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年12月

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 査読

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年12月

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 査読

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年12月

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 査読

Fuyumi Ito, Keiji Nagai, Mitsuo Nakai, Takayoshi Norimatsu

Macromolecular Chemistry and Physics 206 ( 21 ) 2171 - 2176 2005年11月

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) 査読

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年11月

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 査読

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年5月

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 査読

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年4月

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 査読

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年1月

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年1月

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 査読

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年1月

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 査読

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年

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年12月

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年12月

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 査読

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年12月

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 査読

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年12月

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年12月

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年5月

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年5月

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年4月

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 査読

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年2月

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.

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