研究者詳細 - 中井　光男

論文 - 中井　光男

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Proposal on Temperature Control Procedure of the Cryogenic Target for the FIREX Project 査読

Akifumi Iwamoto, Takeshi Fujimura, Mitsuo Nakai, Takayoshi Norimatsu, Keiji Nagai, Ryuji Maekawa, Hitoshi Sakagami

Plasma and Fusion Research 4 ( S1007 ) S1007 - S1007 2009年4月

One of the techniques to produce a uniform solid fuel layer for the Fast Ignition Realization EXperiment (FIREX) target is applying a solid fuel redistribution process. During the redistribution process, temperature control is essential for the FIREX target, because a cone guide, also called a conical laser guide, causes temperature non-uniformity. To minimize its temperature distribution, one possible procedure is temperature control at the cone guide. A radiation plate for indirect temperature control, installed next to the cone guide, is proposed. As the heat input to the radiation plate was varied, the temperature profile of the target was calculated using the ANSYS code. The optimal heat input was evaluated. The feasibility of using a radiation plate is discussed.

Ultrathin amorphization of single-crystal silicon by ultraviolet femtosecond laser pulse irradiation 査読

Izawa Yusaku, Tokita Shigeki, Fujita Masayuki, Nakai Mitsuo, Norimatsu Takayoshi, Izawa Yasukazu

JOURNAL OF APPLIED PHYSICS 105 ( 6 ) 2009年3月

Streaked x-ray backlighting with twin-slit imager for study of density profile and trajectory of low-density foam target filled with deuterium liquid 査読

H. Shiraga, N. Mahigashi, T. Yamada, S. Fujioka, T. Sakaiya, K. Shigemori, M. Nakai, H. Azechi, A. Sunahara

REVIEW OF SCIENTIFIC INSTRUMENTS 79 ( 10 ) 2008年10月

Low-density plastic foam filled with liquid deuterium is one of the candidates for inertial fusion target. Density profile and trajectory of 527 nm laser-irradiated planer foam-deuterium target in the acceleration phase were observed with streaked side-on x-ray backlighting. An x-ray imager employing twin slits coupled to an x-ray streak camera was used to simultaneously observe three images of the target: self-emission from the target, x-ray backlighter profile, and the backlit target. The experimentally obtained density profile and trajectory were in good agreement with predictions by one-dimensional hydrodynamic simulation code ILESTA-1D. (C) 2008 American Institute of Physics. [DOI: 10.1063/1.2966458]

Rayleigh-Taylor instability growth on low-density foam targets 査読

T. Watari, M. Nakai, H. Azechi, T. Sakaiya, H. Shiraga, K. Shigemori, S. Fujioka, K. Otani, K. Nagai, A. Sunahara, H. Nagatomo, K. Mima

PHYSICS OF PLASMAS 15 ( 9 ) 2008年9月

In recent laser fusion programs, foam cryogenic targets have been developed as promising targets which have a great potential to realize efficient nuclear fusion. The foam is porous plastic material having a microstructure inside. We observed the growth of the Rayleigh-Taylor (RT) instability on the foam target with initial surface perturbation for the first time. The measured RT growth rate on the foam target was clearly suppressed in comparison to that of normal-density polystyrene (CH) targets. The values of the RT growth rate for the low-density foam target and the normal-density CH target were 0.84 +/- 0.15 (1/ns) and 1.33 +/- 0.1 (1/ns), respectively. (c) 2008 American Institute of Physics.

Development of TOF Neutron Spectrometer for the measurement of degenerated plasma in Fast Ignition experiment 査読

H. Hosoda, M. Nakai, H. Furukawa, T. Watari, H. Azechi, N. Izumi, Y. Arikawa, Y. Sakawa, S. Dono, T. Fujiwara, K. Mima

5TH INTERNATIONAL CONFERENCE ON INERTIAL FUSION SCIENCES AND APPLICATIONS (IFSA2007) 112 2008年

There are two essential requirements to achieve the Fast Ignition. One is high density compression of main fuel and the other one is additional heating of main fuel by ultra intense laser. Then the experimental determination of both the density of the main fuel before heating laser irradiation and ion temperature after heating laser irradiation is necessary. In the experiment of the Central Ignition, we developed both ion temperature measurement and density measurement, which is based on theoretical degenerated plasma model, by using Time-Of-Flight neutron spectrometer. The main problem in applying this measurement in Fast Ignition experiment is huge amount of high energy x ray, which is generated as a result of heating laser irradiation. Then we installed a total 15-cm thick lead shield as a measure against it. It was confirmed that the newly installed shield achieves x ray attenuation to 5.7 +/- 2.0x10(-4) of previous level by Geant4 MC simulation. And the error for ion temperature measurement was confirmed to be smaller than 0.3 keV in an experiment whose neutron yield was 1.7 +/- 0.2x10(6).

Developments of characterization of the foam shell target for Fast Ignition Realization Experiment-I (FIREX-I) 査読

Fujimura, T, Iwamoto, A, Nakai, M, Norimatsu, T, Nagai, K, Yang, H, Kimura, Y, Sakagami, H, Mito, T, Mima, K

5TH INTERNATIONAL CONFERENCE ON INERTIAL FUSION SCIENCES AND APPLICATIONS (IFSA2007) 112 32066 2008年

Experimental Investigation of Aerosol Formation in Laser Fusion Reactor Chamber by Discharge Method 査読

T. Ohshige, T. Norimatsu, H. Furukawa, M. Nakai, K. Nagai, K. Mima

5TH INTERNATIONAL CONFERENCE ON INERTIAL FUSION SCIENCES AND APPLICATIONS (IFSA2007) 112 2008年

Fast response neutron scintillation detector for FIRE-X 査読

Y. Arikawa, M. Nakai, T. Watari, H. Hosoda, K. Takeda, T. Fujiwara, Y. Furukawa, T. Norimatsu, H. Shiraga, N. Sarukura, H. Azechi

5TH INTERNATIONAL CONFERENCE ON INERTIAL FUSION SCIENCES AND APPLICATIONS (IFSA2007) 112 2008年

We have been developing fast responding neutron detectors with a view to revealing the effect of additional laser heating in FIREX-I (Fast Ignition Realization Experiment) by measuring the burn time with a time resolution under 100 ps at the relatively low neutron yield (about10(6)). The detector is constructed with a thin plastic-scintillaotor (BC-422), a micro-channel-plate photomultiplier tube (MCP-PMT) and a bundle optical fiber as a light-guide. The rise time of a neutron signal from the detector is measured to be 220 ps. The time-determination error for measuring burn time is estimated to be less the +/- 46 ps from the data of characterization experiments measuring the transit time distribution of signals, and calculated values of Doppler broadening and the uncertainty of the scintillation time due to the thickness of the scintillator. In the future with more neutron yield, we will construct a scintillatiion-fiber-streak camera to detect burn history.

Fabrication and Characterization of Planar Cryogenic Targets for GEKKO-XII 査読

T. X. Huang, M. Nakai, K. Shigemori, H. Shiraga, T. Sakaiya, T. Watari, K. Ohtani, T. Shiota, K. Takeda, O. Maegawa, H. Azechi, M. Nagata, T. Norimatsu, K. Nagai, K. Mima, Y. Izawa, T. Mito, K. Iwamoto

5TH INTERNATIONAL CONFERENCE ON INERTIAL FUSION SCIENCES AND APPLICATIONS (IFSA2007) 112 2008年

A planar cryogenic target system was built to simulate the ablator+fuel shell physics in ICF experimental studies. In the center of the target cell, a sandwich target of liquid deuterium was formed, which has open geometry for conventional side-on and face-on backlighting diagnostics. A set of double-flanges comprised a sealing flange and an extra flange, with which the target thickness could be changed using proper spacers. Furthermore, an interferometric method was used to characterize the cryogenic target before laser shot. The in situ target thickness and bulging shape could be obtained with acceptable accuracy. A typical planar cryogenic target was formed with diameter of 2 mm, which comprised three parts: a 7-m thick polyimide film, a layer of liquid deuterium with the thickness of 119 mu m at the center and 100 mu m at the edge, and another 7-mu m thick polyimide film.

Neutron generation from Impact Fast Ignition 査読

T. Watari, T. Sakaiya, H. Azechi, M. Nakai, H. Shiraga, K. Shigemori, H. Hosoda, H. Saito, Y. Arikawa, Y. Sakawa, S. Fujioka, Y. Hironaka, M. Murakami, M. Karasik, J. Gardner, J. Bates, D. Colombant, J. Weber, S. Obenschain, Y. Aglitsky, P. A. Norreys, S. Eliezer, K. Mima

5TH INTERNATIONAL CONFERENCE ON INERTIAL FUSION SCIENCES AND APPLICATIONS (IFSA2007) 112 2008年

We have proposed a new ignition scheme of Fast Ignition, called "Impact Fast Ignition [1] (IFI)", in which a compressed fuel is ignited by impact collision of a fragment of separately imploded fuel. We have started experiments that used CD colliding foils as the fundamental experiment and integrated experiment of the IFI. In the fundamental experiment, we used targets which are consists of two CD foils (thickness of 20 m) with a 600 m separation. We have irradiated one of the CD foils by laser beams of the energy of 2 kJ in total and accelerated. The accelerated CD foil collides with another foil, and neutrons were generated by the nuclear fusion reaction on the heated foil. In this experiment, we measured the neutron yield of 10(6). In the integrated experiment, we used CD shell targets with a gold cone which had a hemispherical impactor (Fig. 1). The shell was imploded using 9 beams and the impactor was accelerated using 3 beams of the GEKKO XII laser system. The laser energy was 350 J per beam. Observed maximum neutron yield was 2x10(6). This yield was 80 times as large as that without impactor. We will present the experimental details and results.

Application of bubble detector in FIREX program 査読

Osamu Maegawa, Takashi Fujiwara, Mitsuo Nakai, Hiroyuki Shiraga

5TH INTERNATIONAL CONFERENCE ON INERTIAL FUSION SCIENCES AND APPLICATIONS (IFSA2007) 112 2008年

In a Fast Ignition Realization Experiment (FIREX), measurement of the primary and the secondary neutron yield is one of the key diagnostics. However, gamma-ray background generated by an ultra-short pulse laser irradiation makes it difficult to measure the neutron yield in the fast ignition experiment. We adopted a bubble neutron detector as a promising gamma-insensitive detector to be developed and started to examine the feasibility of the detector using commercially available dosimeters provided from BTI inc. [1].

Solution viscosity adjustable phloroglucinolcarboxylic acid / formaldehyde applied in extremely thin shell fusion target fabrication 査読

H. Yang, K. Nagai, M. Nakai, T. Norimatsu

5TH INTERNATIONAL CONFERENCE ON INERTIAL FUSION SCIENCES AND APPLICATIONS (IFSA2007) 112 2008年

Capsuliform fusion target was prepared by using the O(O) / W / O(I) emulsion process. Phloroglucinolcarboxylic acid / formaldehyde (PF) is expected to be used as the water phase (W) solution which then gelates to be the shell of the capsule. The density of the shell should be low to obtain high laser gain. Phloroglucinolcarboxylic acid had addition and condensation reaction with formaldehyde under basic condition to form linear polymer first. The nano-scale linear polymers were then linked via noncovalent interactions, such as hydrogen bonding, van der Waals, to continue the gelation process. The type and amount of the base catalyst used in the reaction can affect the polymerization of PF, including the gelation rate and gelation concentration. By changing the basic condition of the reaction, the proper viscosity of 9x10(-5) for capsuliform target fabrication was reached and extremely thin gel shell thickness of 17 mu m with low polymer concentration of 26.3mg/cm(3) was obtained.

Temperature Measurement of Preheated Planar-Cryogenic Targets 査読

K. Otani, K. Shigemori, D. Ichinose, T. Sakaiya, A. Sunahara, Y. Sakawa, M. Nakai, H. Shiraga, H. Azechi, K. Mima

5TH INTERNATIONAL CONFERENCE ON INERTIAL FUSION SCIENCES AND APPLICATIONS (IFSA2007) 112 2008年

The temperature measurement of preheated target is reported. Inertial confinement fusion (ICF) targets should be imploded with a low adiabat for achievement of high density compression. The high energy photons and electrons from ablation plasma can preheat the uncompressed fuel and disturb the low adiabat compression. Preheat has to be evaluated and suppressed for ICF targets. The planar target of cryogenic deuterium was developed for measurement of the self emission from the rear surface. Experiment indicated that the x-ray preheating is more effective than that of non-local electron heat transport at the laser intensity of 10(14) W/cm(2).

Study on a fuel layering sequence of the foam target for the FIREX project 査読

Iwamoto, A, Fujimura, T, Nakai, M, Nagai, K, Norimatsu, T, Maekawa, R, Mito, T, Sakagami, H, Motojima, O, Azechi, H, Mima, K

5TH INTERNATIONAL CONFERENCE ON INERTIAL FUSION SCIENCES AND APPLICATIONS (IFSA2007) 112 32067 2008年

Reduction of the Rayleigh-Taylor instability growth with cocktail color irradiation 査読

K. Otani, K. Shigemori, T. Sakaiya, S. Fujioka, A. Sunahara, M. Nakai, H. Shiraga, H. Azechi, K. Mima

PHYSICS OF PLASMAS 14 ( 12 ) 2007年12月

A novel method for reducing the Rayleigh-Taylor instability (RTI) growth in inertial confinement fusion (ICF) targets is reported. It is well known that high-density compression of ICF targets is potentially prevented by the RTI. Previous studies [K. Shigemori , Phys. Rev. Lett. 78, 250 (1997), S. G. Glendinning , Phys. Rev. Lett. 78, 3318 (1997), and H. Azechi , Phys. Plasmas 4, 4079 (1997)] have indicated that nonlocal electron heat transport enhances the effect on the ablative stabilization of the RTI growth with long wavelength laser irradiation. Planar target experiments, using a small fraction of a long wavelength laser (lambda=0.53 or 1.05 mu m) in addition to the main drive laser (lambda=0.35 mu m), were conducted to verify the RTI reduction by inducing the effect of the nonlocal electron heat transport. The measured RTI growth rate for this "cocktail-color" laser irradiation was clearly reduced from that for the "single-color" short-wavelength laser irradiation. The experimental growth factors are in good agreement with the ablative RTI formula coupled with a one-dimensional Fokker-Planck simulation code. (c) 2007 American Institute of Physics.

Recent results and future prospects of laser fusion research at ILE, Osaka 査読

K. Mima, K. A. Tanaka, R. Kodama, T. Johzaki, H. Nagatomo, H. Shiraga, N. Miyanaga, M. Murakami, H. Azechi, M. Nakai, T. Norimatu, K. Nagai, T. Taguchi, H. Sakagami

EUROPEAN PHYSICAL JOURNAL D 44 ( 2 ) 259 - 264 2007年8月

Reviewed are the present status of the fast ignition researches. Since 1997, the fast ignition experiment and theory researches have been extensively continued at the Institute of Laser Engineering of Osaka University. In particular, the cone-shell target experiments and simulation research have been progressing. In order to demonstrate heating of imploded high density plasma to the ignition temperature, in the April of 2003, the construction of heating laser of 10 kJ/10 ps/1.06 mu m (Laser for Fusion Experiment; LFEX), for FIREX-I (Fast Ignition Realization Experiment) has started. The fabrication of DT foam cryogenic cone target is also under development as a collaboration program between Osaka University and NIFS (National Institute for Fusion Science). The LFEX will be completed in 2008. After the completion of LFEX, the foam cryogenic cone shell target experiment will start in 2008. As a new approach toward a compact ignition, an impact fusion has been proposed, where the ablative acceleration to the order of 10(8) cm/s is the key issue. The ablation acceleration related to the impact fusion has been explored by experiments.

Foam structure of xerogel prepared via ring-opening reaction between epoxy groups attached on the side chain of polystyrene 査読

Kentaro Yamanaka, Keiji Nagai, Nobukatsu Nemoto, Kaori Nomura, Tomonori Shimoyama, Kei Tanji, Tomoya Tanji, Mitsuo Nakai, Takayoshi Norimatsu

FUSION SCIENCE AND TECHNOLOGY 51 ( 4 ) 665 - 672 2007年5月

This paper deals with a new foam material containig polysytrene and its oxirane derivative. A monomer, 4-vinylphenyloxirane (MI), was prepared from 4-chlorostyrene. Polystyrene-based copolymers using styrene and M1 were prepared by free radical copolymerization using azo-bis(isobutyronitrile) (AIBN) as an initiator. The solutions of the obtainedpolystyrene-based copolymers in 4-chlorotoluene were gelated by the addition of a cationic initiator, which caused crosslinking via ring-opening polymerization of the pendant cyclic moieties. SEM images of the dried gel show various foam structures. The formation mechanism of the micro- and nano-structure was explained from the view point of the affinity of the monomer unit and the solvent. The homopolymer of 4-vinyphenylolxirane showed the finest and most uniform structure.

Laser machining of RF foam by second harmonics of Nd : Yag laser 査読

Takeshi Fujimura, Takayoshi Norimatsu, Mitsuo Nakai, Keiji Nagai, Akifumi Iwamoto, Kunioki Mima

FUSION SCIENCE AND TECHNOLOGY 51 ( 4 ) 677 - 681 2007年5月

A way to make a hole in a resorcinol-formaldehyde (RF) foam shell target is described. A target used in fast ignition (FI) experiments consists of an RF foam shell and a guide cone. The fragile RF foam cannot accept conventional mechanical drilling or laser machining. We used the second harmonics of a Nd:YAG laser (532nm) to bore a hole for the cone by utilizing thermal decomposition of the RF foam.
To optimize the cutting condition, the thermal characteristic and absorption spectrum of the RF foam were measured with a thermo-gravimetric meter and a spectrometer respectively. Then, using these results, relationships between the laser power and cutting speed were optimized for RF foams with several densities.

Preliminary results of fuel layering on the cryogenic target for the firex project 査読

Iwamoto, A, Maekawa, R, Mito, T, Sakagami, H, Motojima, O, Nakai, M, Nagai, K, Fujimura, T, Norimatsu, T, Azechi, H, Mitna, K

FUSION SCIENCE AND TECHNOLOGY 51 ( 4 ) 753 - 757 2007年5月

Comprehensive diagnosis of growth rates of the ablative Rayleigh-Taylor instability 査読

H. Azechi, T. Sakaiya, S. Fujioka, Y. Tamari, K. Otani, K. Shigemori, M. Nakai, H. Shiraga, N. Miyanaga, K. Mima

PHYSICAL REVIEW LETTERS 98 ( 4 ) 2007年1月

The growth rate of the ablative Rayleigh-Taylor instability is approximated by gamma=root kg/(1+kL)-beta km/rho(a), where k is the perturbation wave number, g the gravity, L the density scale length, m the mass ablation rate, and rho(a) the peak target density. The coefficient beta was evaluated for the first time by measuring all quantities of this formula except for L, which was taken from the simulation. Although the experimental value of beta=1.2 +/- 0.7 at short perturbation wavelengths is in reasonably good agreement with the theoretical prediction of beta=1.7, it is found to be larger than the prediction at long wavelengths.

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