Faculty Profiles - Nakai Mitsuo

Papers - Nakai Mitsuo

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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.

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Papers - Nakai Mitsuo