論文 - 中井　光男

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

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年5月

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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 査読

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年4月

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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 査読

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

PHYSICAL REVIEW E   65 ( 4 )   2002年4月

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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 査読

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年4月

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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 査読

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年4月

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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 査読

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年

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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 査読

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年

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年1月

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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年1月

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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年11月

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年6月

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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 査読

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年3月

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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.

C. レーザーエネルギー応用

山神 晋, 中山 斌義, Yu W., 佐々木 明, 内海 隆行, 森林 健悟, 河内 哲哉, 加道 雅孝, 長谷川 登, 上島 豊, 田島 俊樹, 大道 博行, 南雲 雄三, 林 茂樹, 八木 隆志, 松村 健, 山崎 将, 小島 勇夫, 本田 一匡, 下浦 厚志, 望月 孝晏, 宮本 修治, 長友 英夫, 天野 壮, 唐 華興, 吉住 泰明, 畦地 博, 中井 光男, Joyeux Denis, Phalippou Daniel, Jamelot Gerard, 高橋 栄一, 奥田 功, 鈴木 将之, 松本 裕治, 松嶋 功, 加藤 進, 桑原 研爾, 大和田野 芳郎, 岩崎 優, 実野 孝久, 本越 伸二, 西 紀昭, 中塚 正大, 村上 陽一, 森 浩一, 小紫 公也, 荒川 義博, 石本 雅嗣, 内田 成明, 今崎 一夫, 周 香林, 阪部 周二, 河島 信樹, 沖原 伸一朗, 崔日 祐, 佐藤 文信, 島田 岳洋, 高橋 浩司, 坂部 祐介, 乗松 孝好, 井澤 靖和, 飯田 敏行, 中島 一久, 金沢 修平, 神門 正城, Fiedorowicz H., 近藤 修司, 小瀧 秀行, 出羽 英紀, 細貝 知直, 依田 正樹, 馬場 洋介, 向井 成彦, 佐野 雄二, 荻須 達樹, 山浦 道照, Bartnik A., 猪原 哲, 佐藤 三郎, 山部 長兵衛, 野澤 俊一, 島田 義則, 緒方 淳寿, 山中 龍彦, 山中 千代衛, 石窪 雄二, 川端 欣哉, Rakowski R.

レーザー研究   28 ( 0 )   69 - 71,74   2000年

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

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年

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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 査読

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年

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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 査読

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年2月

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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 査読

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

FUSION ENGINEERING AND DESIGN   44   205 - 208   1999年2月

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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 査読

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

FUSION ENGINEERING AND DESIGN   44   199 - 203   1999年2月

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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 査読

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年1月

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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 査読

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年

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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.