研究者詳細 - 中井　光男

論文 - 中井　光男

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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年11月

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 査読

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

PHYSICAL REVIEW LETTERS 80 ( 15 ) 3415 - 3415 1998年4月

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

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年2月

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年

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 査読

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年11月

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 査読

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

IEEE TRANSACTIONS ON NUCLEAR SCIENCE 44 ( 3 ) 890 - 893 1997年6月

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

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年3月

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年1月

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年1月

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 査読

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年

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 査読

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年

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 査読

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年

Experiments on indirect/direct hybrid drive scheme 査読

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年

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

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年

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 査読

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年

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 査読

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年

Laser fusion research at ILE Osaka University 査読

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年12月

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

Laser Interaction and Related Plasma Phenomena, pp.131-135 1996年7月

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

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年5月

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 査読

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年3月

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.

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