Faculty Profiles - Nakai Mitsuo

Papers - Nakai Mitsuo

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Laser surface inspections: Fundamentals and applications to monitor inner surface conditions of nuclear fusion reactor chambers Reviewed

Koichi Kasuya, S. Ozawa, T. Norimatsu, H. Azechi, K. Mima, S. Nakai, S. Suzuki, B. Budner, W. Mroz, N. Kasuya, W. Kasuya, Kei Kasuya, Y. Izawa, H. Furukawa, Y. Shimada, T. Yamanaka, M. Nakai, K. Nagai, K. Yokoyama, K. Ezato, M. Enoeda, M. Akiba, A. Prokopiuk

Proceedings of SPIE - The International Society for Optical Engineering 7751 2010

The most recent fundamental research results to investigate surface erosions of nuclear fusion candidate chamber materials are described in short. We used a commercial surface profiler with a red semiconductor laser. Various material surfaces ablated and eroded by a rather short pulse electron beam and a short pulse ArF laser light were measured with this surface profiler and the associated three-dimensional analysis software. Threshold input levels for various sample surface erosions with electron and laser beams were clearly decided for the first time with our new method in this article. After the above fundamental results were gathered, the methods to inspect inner surface conditions of nuclear fusion reactor chambers were newly proposed with various kinds of laser displacement sensors. The first one is the erosion monitor with the above profiler, and the second one is the laser induced ultrasonic wave detection method to inspect deeper surface layers than the first one. © 2010 Copyright SPIE - The International Society for Optical Engineering.

Pr doped Li-6 glass scintillator for Inertial Confinement Fusion neutron diagnostics Reviewed

Yasunobu Arikawa, Kouhei Yamanoi, Tomoharu Nakazato, Elmer Surat Estacio, Toshihiko Shimizu, Nobuhiko Sarukura, Mitsuo Nakai, Takayoshi Norimatsu, Youichirou Hironaka, Hiroshi Azechi, Takahiro Murata, Shigeru Fujino, Hideki Yoshida, Kei Kamada, Yoshiyuki Usuki, Toshihisa Suyama, Akira Yoshikawa, Nakahiro Sato, Hirofumi Kan

2010 CONFERENCE ON LASERS AND ELECTRO-OPTICS (CLEO) AND QUANTUM ELECTRONICS AND LASER SCIENCE CONFERENCE (QELS) 2010

Present status and future prospect of Fast Ignition Realization Experiment (FIREX) Project at ILE, Osaka Reviewed

H. Nishimura, H. Azechi, K. Mima, Y. Fujimoto, S. Fujioka, H. Homma, T. Jitsuno, T. Johzaki, M. Koga, J. Kawanaka, T. Kawasaki, N. Miyanaga, H. Murakami, M. Murakami, H. Nagatomo, N. Morio, K. Nagai, M. Nakai, T. Nakamura, T. Nakazato, Y. Nakata, K. Nishihara, T. Norimatsu, Y. Sakawa, N. Sarukura, K. Shigemori, T. Shimizu, H. Shiraga, K. Sueda, K. Tsubakimoto, A. Iwamoto, T. Mito, H. Sakagami, M. Isobe, T. Ozaki, O. Motojima, R. Kodama, K. A. Tanaka, H. Habara, K. Kondo, Y. Nakao, Y. Sentoku, A. Sunahara, T. Taguchi, T. Kanabe

2ND INTERNATIONAL CONFERENCE ON ULTRA-INTENSE LASER INTERACTION SCIENCE 1209 83 - + 2010

Thermonuclear ignition and subsequent burn are key physics for achieving laser fusion. In fast ignition, a highly compressed fusion fuel generated with multiple ns-laser beams is rapidly heated with a large energy, ps-laser pulse in prior to core disassembly. This scheme has a high potential to achieve ignition and burn since driver energy required for high fusion gain is predicted to be about one tenth of that needed for the central ignition scheme. In Japan, Fast Ignition Realization Experiment (FIREX) project has been started to clarify the physics of energy transport and deposition in the core plasma and to demonstrate fuel temperature of above 5 keV. After the success, FIREX-I will be followed by the second phase of the project (FIREX-II) to demonstrate ignition and burn. LFEX laser, designed to deliver a laser pulse of 10 kJ in 10 ps, are operational and the first phase of FIREX experiments has been stated. A new target is proposed to attain dense compression of fuel and improve laser-core coupling efficiency by adopting double-cone structure, a low-density inner liner, low-Z outer coating, and Br-doped fuel shell. In this paper, present status and near term prospects of the FIREX-I project will be reported together with activities on target designing, laser development, and plasma diagnostics.

Study on possible fuel layering sequence for FIREX target Reviewed

A. Iwamoto, T. Fujimura, M. Nakai, K. Nagai, T. Norimatsu, H. Azechi, R. Maekawa, H. Sakagami

SIXTH INTERNATIONAL CONFERENCE ON INERTIAL FUSION SCIENCES AND APPLICATIONS, PARTS 1-4 244 2010

A new procedure of fuel layering for the Fast Ignition Realization Experiment (FIREX) target is proposed. A conical laser guide heating technique was experimentally demonstrated in principle as the followings. It employed the target consisting of a polystyrene (PS) shell, a fill tube and a conical laser guide. At first, liquid fuel was fed into the shell and existed around the conical laser guide because the surface tension of the fuel must cause it. Then, it was solidified. The laser light provided a heat source to the conical laser guide so that the solid fuel was moved to the other interior of the shell. This process resulted in missing solid fuel around the conical laser guide. To fill the vacant space, liquid fuel was added as temperature was raised to the melting point. After the liquid fuel addition, temperature was lowered to the solidification point again. During this process, most of the solid fuel could survive.

Pr3+-doped fluoro-oxide lithium glass as scintillator for nuclear fusion diagnostics Reviewed

Yasunobu Arikawa, Kohei Yamanoi, Tomoharu Nakazato, Elmer Surat Estacio, Toshihiko Shimizu, Nobuhiko Sarukura, Mitsuo Nakai, Takayoshi Norimatsu, Hiroshi Azechi, Takahiro Murata, Shigeru Fujino, Hideki Yoshida, Kei Kamada, Yoshiyuki Usuki, Toshihisa Suyama, Akira Yoshikawa, Nakahiro Sato, Hirofumi Kan

REVIEW OF SCIENTIFIC INSTRUMENTS 80 ( 11 ) 2009.11

Experimental results are presented on the neutron scintillating properties of a custom-designed Pr3+(praseodymium)-doped lithium (Li) glass. Luminescence was observed at 278 nm wavelength, originating from the 5d-4f transition. Time-resolved measurements yielded about 20 ns decay times for ultraviolet and x-ray excitation while much faster decay times of about 6 ns were observed for alpha particle and neutron excitation. Actual time-of-flight data in laser fusion experiments at the GEKKO XII facility of the Institute of Laser Engineering, Osaka University reveal that it can clearly discriminate fusion neutrons from the much stronger x-rays signals. This material can promise improved accuracy in future scattered neutron diagnostics. (C) 2009 American Institute of Physics. [doi:10.1063/1.3254444]

Plasma physics and laser development for the Fast-Ignition Realization Experiment (FIREX) Project Reviewed

H. Azechi, K. Mima, Y. Fujimoto, S. Fujioka, H. Homma, M. Isobe, A. Iwamoto, T. Jitsuno, T. Johzaki, R. Kodama, M. Koga, K. Kondo, J. Kawanaka, T. Mito, N. Miyanaga, O. Motojima, M. Murakami, H. Nagatomo, K. Nagai, M. Nakai, H. Nakamura, T. Nakamura, T. Nakazato, Y. Nakao, K. Nishihara, H. Nishimura, T. Norimatsu, T. Ozaki, H. Sakagami, Y. Sakawa, N. Sarukura, K. Shigemori, T. Shimizu, H. Shiraga, A. Sunahara, T. Taguchi, K. A. Tanaka, K. Tsubakimoto

NUCLEAR FUSION 49 ( 10 ) 2009.10

Since the approval of the first phase of the Fast-Ignition Realization Experiment (FIREX-I), we have devoted our efforts to designing advanced targets and constructing a petawatt laser, which will be the most energetic petawatt laser in the world. Scientific and technological improvements are required to efficiently heat the core plasma. There are two methods that can be used to enhance the coupling efficiency of the heating laser to the thermal energy of the compressed core plasma: adding a low-Z foam layer to the inner surface of the cone and employing a double cone. The implosion performance can be improved in three ways: adding a low-Z plastic layer to the outer surface of the cone, using a Br-doped plastic ablator and evacuating the target centre. An advanced target for FIREX-I was introduced to suit these requirements. A new heating laser (LFEX) has been constructed that is capable of delivering an energy of 10 kJ in 10 ps with a 1 ps rise time. A fully integrated fast-ignition experiment is scheduled for 2009.

Fabrication of aerogel capsule, bromine-doped capsule, and modified gold cone in modified target for the Fast Ignition Realization Experiment (FIREX) Project Reviewed

Keiji Nagai, H. Yang, T. Norimatsu, H. Azechi, F. Belkada, Y. Fujimoto, T. Fujimura, K. Fujioka, S. Fujioka, H. Homma, F. Ito, A. Iwamoto, T. Jitsuno, Y. Kaneyasu, M. Nakai, N. Nemoto, H. Saika, T. Shimoyama, Y. Suzuki, K. Yamanaka, K. Mima

NUCLEAR FUSION 49 ( 9 ) 2009.9

The development of target fabrication for the Fast Ignition Realization EXperiment (FIREX) Project is described in this paper. For the first stage of the FIREX Project (FIREX-I), the previously designed target has been modified by using a bromine-doped ablator and coating the inner gold cone with a low-density material. A high-quality bromine-doped capsule without vacuoles was fabricated from bromine-doped deuterated polystyrene. The gold surface was coated with a low-density material by electrochemical plating. For the cryogenic fuel target, a brand new type of aerogel material, phloroglucinol/formaldehyde (PF), was investigated and encapsulated to meet the specifications of 500 mu m diameter and 20 mu m thickness, with 30 nm nanopores. Polystyrene-based low-density materials were investigated and the relationship between the crosslinker content and the nanopore structure was observed.

Developments of nuclear diagnostics for fast ignition experiments in laser fusion Reviewed

H. Nakamura, Y. Arikawa, H. Habara, M. Isobe, R. Kodama, M. Koga, M. Nakai, H. Nishimura, T. Ozaki, Y. Sakawa, N. Sarukura, H. Shiraga, Ka. Tanaka, H. Azechi

ABSTRACTS OF PAPERS OF THE AMERICAN CHEMICAL SOCIETY 238 2009.8

TEMPERATURE CONTROL IN A CRYOGENIC TARGET WITH A CONICAL LASER GUIDE FOR FUEL LAYERING Reviewed

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

FUSION SCIENCE AND TECHNOLOGY 56 ( 1 ) 427 - 431 2009.7

Fuel layering of a cryogenic target with a conical laser guide such as the FIREX target is complicated because of its non-spherical symmetry appearance. To simplify the layering, a foam layer is planned to utilize as a supporting material of fuel. Ideally, the foam shell has self-fuel-layering ability at a liquid state owing to the capillarity of the foam material. For stable fuel compression in laser experiments, the fuel must be solid with a lower saturated pressure. The transition to a solid state expects to cause random fuel crystallization and voids from the density difference between liquid and solid A volumetric heat load might help to finish fuel layering even in the foam shell. Solid fuel redistribution will ignore the foam boundary. Temperature control in the target, therefore, is required during the formation of a uniform layer. For the rough estimation of the target temperature, the possibility of the ANSYS code was confirmed compared with the experiment using a dummy target. Then, steady state temperature profiles of the FIREX target were calculated using the ANSYS code. Temperature control to practically realize a uniform solid fuel layer in the FIREX target is discussed.

Experimental Evidence of Impact Ignition: 100-Fold Increase of Neutron Yield by Impactor Collision Reviewed

H. Azechi, T. Sakaiya, T. Watari, M. Karasik, H. Saito, K. Ohtani, K. Takeda, H. Hosoda, H. Shiraga, M. Nakai, K. Shigemori, S. Fujioka, M. Murakami, H. Nagatomo, T. Johzaki, J. Gardner, D. G. Colombant, J. W. Bates, A. L. Velikovich, Y. Aglitskiy, J. Weaver, S. Obenschain, S. Eliezer, R. Kodama, T. Norimatsu, H. Fujita, K. Mima, H. Kan

PHYSICAL REVIEW LETTERS 102 ( 23 ) 2009.6

We performed integrated experiments on impact ignition, in which a portion of a deuterated polystyrene (CD) shell was accelerated to about 600 km/s and was collided with precompressed CD fuel. The kinetic energy of the impactor was efficiently converted into thermal energy generating a temperature of about 1.6 keV. We achieved a two-order-of-magnitude increase in the neutron yield by optimizing the timing of the impact collision, demonstrating the high potential of impact ignition for fusion energy production.

Shock Hugoniot and temperature data for polystyrene obtained with quartz standard Reviewed

N. Ozaki, T. Sano, M. Ikoma, K. Shigemori, T. Kimura, K. Miyanishi, T. Vinci, F. H. Ree, H. Azechi, T. Endo, Y. Hironaka, Y. Hori, A. Iwamoto, T. Kadono, H. Nagatomo, M. Nakai, T. Norimatsu, T. Okuchi, K. Otani, T. Sakaiya, K. Shimizu, A. Shiroshita, A. Sunahara, H. Takahashi, R. Kodama

PHYSICS OF PLASMAS 16 ( 6 ) 2009.6

Equation-of-state data, not only pressure and density but also temperature, for polystyrene (CH) are obtained up to 510 GPa. The region investigated in this work corresponds to an intermediate region, bridging a large gap between available gas-gun data below 60 GPa and laser shock data above 500 GPa. The Hugoniot parameters and shock temperature were simultaneously determined by using optical velocimeters and pyrometers as the diagnostic tools and the alpha-quartz as a new standard material. The CH Hugoniot obtained tends to become stiffer than a semiempirical chemical theoretical model predictions at ultrahigh pressures but is consistent with other models and available experimental data.

SMOOTH MEMBRANE FORMATION ON RESORCINOL-FORMALDEHYDE AEROGEL BALLS GELATED USING A BASIC PHASE-TRANSFER CATALYST Reviewed

Fuyumi Ito, Naotake Nakamura, Keiji Nagai, Mitsuo Nakai, Takayoshi Norimatsu

FUSION SCIENCE AND TECHNOLOGY 55 ( 4 ) 465 - 471 2009.5

Low-density foam balls with a diameter of similar to 1 mm were produced from a density-matched emulsion consisting of a resorcinol-formaldehyde (RF) aqueous solution (W) and an exterior oil of carbontetrachloride/(mineral oil) (O). Phase-transfer catalysts such as an alkyl amine were dissolved in the exterior oil, following which the catalyst moved into the RF solution from the exterior oil. A gelation process was monitored by a complete gelation test. When the basic catalysts were used at room temperature as a phase-transfer catalyst, gelation occurred within 30 to 120 min, whereas when the acidic catalyst was used, gelation occurred within 20 to 30 min at room temperature. When similar to 0.39 wt% of triethylamine and tri(n-butyl)amine in the oil phase were based, complete gelation took place. A basic catalyst with a long alkyl chain such as dimethyl(n-hexyl)amine did not induce gelation. The gelated balls obtained using the basic catalyst with a short alkyl chain were dried by extraction using super-critical fluid CO2 and the solvent was replaced with 2-propanol to produce the foam structure. Except 0.39 wt% tri(n-butyl)amine, the basic catalysts yielded foam balls with higher densities of 173 to 184 mg/cm(3) as compared to those obtained from a benzoic acid catalyst, namely, 158 mg/cm(3). The density difference can be attributed to the inclusion of the basic catalyst in the RF solution. Scanning electron microscopy images revealed a surface membrane formation, which can be explained by local concentration at the W/O interface. The cell size of the bulk foam was observed to depend on the catalysts, and it was surmised that the cell sizes varied because of the different gelation rates. A smooth surface membrane tri(n-butyl)amine was used as a catalyst. The membrane obtained on using a basic phase-transfer catalyst was smoother than that obtained on using an acid catalyst. Such a smooth membrane is useful for coating the ablation layer of foam capsule targets.

Manufacturing of leak check of shell targets for FIREX-I project Reviewed

Takeshi Fujimura, Mitsuo Nakai, Akifumi Iwamoto, Keiji Nagai, Hirofumi Homma, Ken-ichi Tanabe, Takayoshi Norimatsu

Plasma and Fusion Research 4 ( S1010 ) S1010 - S1010 2009.4

This article reports the latest progress in the manufacture of shell targets used for the first stage of the Fast Ignition Realization Experiment (FIREX-I). In the project, the targets are cooled to cryogenic temperature and filled with hydrogen isotope fuel through a gas feed tube. If the target has a leak or the gas feeder is blocked, the experiments cannot be carried out successfully and waste much time. The authors have developed a system to check integrity of the targets. SF6 is used instead of H2 or D2 because of its high refractive index and low diffusivity. When SF6 is loaded into the target, the optical path length that passes through a target is longer than that of an evacuated target. The difference can be measured with an interferometer. Analyzing the interference images, it is possible to know whether the gas feeder is blocked and a leak is present. The validity of the system was experimentally confirmed.

Advanced target design for the FIREX-I project Reviewed

Hiroshi AZECHI, Mitsuo NAKAI, Hirofumi HOMMA, Tomoyuki JOHZAKI, Mayuko KOGA, Kunioki MIMA, Noriaki MIYANAGA, Masakatsu MURAKAMI, Hideo NAGATOMO, Keiji NAGAI, Tatsufumi NAKAMURA, Katsunobu NISHIHARA, Hiroaki NISHIMURA, Takayoshi NORIMATSU, Youichi SAKAWA, Keisuke SHIGEMORI, Hiroyuki SHIRAGA, Akifumi IWAMOTO, Toshiyuki MITO, Hitoshi SAKAGAMI, Osamu MOTOJIMA, Ryosuke KODAMA, Kazuo A. TANAKA, Atsushi SUNAHARA

Plasma Fusion Res. 4 ( S1001 ) S1001 - S1001 2009.4

Cryogenically cooled foam shells with deuterium and tritium fuels are expected to be utilized in the fast ignition realization experiment project of ILE, Osaka University, to demonstrate efficient heating of properly compressed fuel plasmas. These targets consist of a foam shell with solid fuel and a conical light guide for additional heating with an ultra-high intensity laser beam, in accordance with previous preliminary experiments [R. Kodama et al., Nature 412, 798 (2001).] Recent theoretical predictions and elemental experiments have suggested some advanced modifications to enhance the coupling efficiency of fast heating and improve implosion performance. The five major points of these improvements are as follows: 1) use of a low-Z foam layer on the inner surface of the cone; 2) use of a double-layered cone as a light guide; 3) use of a low-Z plastic layer on the outer surface of the cone; 4) adding a Br-doped plastic ablator to the fuel capsule; and 5) evacuation of the target center.

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

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

Plasma and Fusion Research 4 ( S1007 ) S1007 - S1007 2009.4

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 Reviewed

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

JOURNAL OF APPLIED PHYSICS 105 ( 6 ) 2009.3

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

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

REVIEW OF SCIENTIFIC INSTRUMENTS 79 ( 10 ) 2008.10

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 Reviewed

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 ) 2008.9

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 Reviewed

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

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) Reviewed

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

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Papers - Nakai Mitsuo