Faculty Profiles - Nakai Mitsuo

Papers - Nakai Mitsuo

Division display 161 - 180 of about 304 ／ All the affair displays >>

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

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

JOURNAL DE PHYSIQUE IV 133 27 - 28 2006.6

Electrochemical fabrication of low density metal foam with mono-dispersed-sized micro- and submicro-meter pore Reviewed

K Nagai, D Wada, M Nakai, T Norimatsu

FUSION SCIENCE AND TECHNOLOGY 49 ( 4 ) 686 - 690 2006.5

This paper deals with the fabrication of low-density metal using micro-template and electrochemical plating techniques. Tin and gold foam films were demonstrated For both cases, porous foam plating required 0.5 V negatively higher bias potential than that for conventional metal plating. The electric current density values for them are smaller than those for bulk metal plating. In spite of these differences, the coulomb efficiency was almost the same as those for bulk metal plating. The density was almost close to the rest of closed packing density; 23 % of bulk metal for gold and 20 % of bulk metal for tin. These low-density foams will be applied for extreme ultraviolet (EUV) generation or other application through laser produced plasma.

Hugoniot measurement of diamond under laser shock compression up to 2 TPa Reviewed

H Nagao, KG Nakamura, K Kondo, N Ozaki, K Takamatsu, T Ono, T Shiota, D Ichinose, KA Tanaka, K Wakabayashi, K Okada, M Yoshida, M Nakai, K Nagai, K Shigemori, T Sakaiya, K Otani

PHYSICS OF PLASMAS 13 ( 5 ) 2006.5

Hugoniot data of diamond was obtained using laser-driven shock waves in the terapascal range of 0.5-2 TPa. Strong shock waves were generated by direct irradiation of a 2.5 ns laser pulse on an Al driver plate. The shock wave velocities in diamond and Al were determined from optical measurements. Particle velocities and pressures were obtained using an impedance matching method and known Al Hugoniot. The obtained Hugoniot data of diamond does not show a marked difference from the extrapolations of the Pavlovskii Hugoniot data in the TPa range within experimental errors. (c) 2006 American Institute of Physics.

Optimization of gelation to prepare hollow foam shell of resorcinol-formalin using a prase-transfer catalyst Reviewed

F Ito, K Nagai, M Nakai, T Norimatsu

FUSION SCIENCE AND TECHNOLOGY 49 ( 4 ) 663 - 668 2006.5

We studied the gelation of an RF foam shell using a phase-transfer catalyst and density-match non-volatile silicon oil. A phase-transfe catalyst circumvent the problem of density-mismatch and achieve gelation at room temperature, by which the catalyst is contained in the outer oil (O-o,) phase, and is then gradually transferred into the RF droplets. For the O-o phase, we used non-volatile silicon oil as a non-hazardous material instead of a toxic (mineral oil)/carbontetrachloride.
Vigorous agitation conditions were optimized based on three experiments. An emulsion was produced using a droplet generator, and was injected into a drum containg a mixture of 0.39% acetic acid and silicon oil. The drum was rotated and its speed were increased to 95 rpm within 15 minutes. Five minutes later, the rotation speed was increased to 120 rpm (maximum rotation speed), which was maintained for 1 minute, there after reduced to 95 rpm for 39 minutes.

Polystyrene based foam materials for cryogenic targets of fast ignition realization experiment (FIREX) Reviewed

N Nemoto, K Nagai, Y Ono, K Tanji, T Tanji, M Nakai, T Norimatsu

FUSION SCIENCE AND TECHNOLOGY 49 ( 4 ) 695 - 700 2006.5

This paper deals with the development of materials without volume change in the formation of uniform low density foam capsules with fine structures. Two monomers, i.e., 5-(4-vinylbenzyl)oxymethyl-5-methyl-1,3dioxane-2-thione (M1) and 4-vinylphenyloxirane (M2), were prepared as the comonomers polymerized with styrene. Polystyrene-based copolymers using styrene and M1 or M2 were prepared by free radical copolymerization using azobis(isoburyronitrile) (AIBN) as an initiator. The solutions of the obtained polystyrene-based copolymers in benzenel/dichloromethane mixture or 4-chlorotoluene were gelated by the addition of a cationic initiator, which caused cross-linking via ring-opening polymerization of the pendant cyclic moieties. The gel was transformed into an aerogel by exchanging solvent to 2-propanol, and removal of 2-propanol using supercritical CO2. SEM images of a cross sectional view of the aerogel indicated that sub-micrometer voids were distributed randomly, and most of parts look filled bulk morphology. The density of the gel obtained from the present polystyrene-based copolymers was estimated to be 200 mg/cm(3), which implies existence of vacancies without observation in the SEM image, suggesting the extremely fine cell structure.

Tin-polymer composite on a rotating drum as a high repetition rate laser target for extreme ultraviolet generation Reviewed

Y Yasuda, QC Gu, K Nagai, M Nakai, T Norimatsu, S Fujioka, H Nishimura, M Nakatsuka

FUSION SCIENCE AND TECHNOLOGY 49 ( 4 ) 691 - 694 2006.5

High repetition rate irradiation of a laser on target is necessary for practical operation of an extreme ultraviolet (EUV) light source. A rotating drum with a tin composite film was fabricated for this purpose. Uniformly tin-dispersed plastic film was prepared from hydroxypropyl cellulose (HPC) and tin source solution of SnCl4/ethanol/H2O. It was transparent in the visible to near infrared region. The film was coated on an aluminum rotating drum from HPC-Sn solution. When this solution was coated on aluminum rotating target drum directly, the drum was corroded. Therefore an alternative method was developed starting with tin(tertbutoxide) instead of SnCl4. The later solution was used for coating on aluminum rotating target drum directly.

Low-density-plastic-foam capsule of resorcinol/formalin and (phloroglucinolcarboxylic acid)/formalin resins for fast-ignition realization experiment (FIREX) in laser fusion research Reviewed

F Ito, K Nagai, M Nakai, T Norimatsu, A Nikitenko, S Tolokonnikov, E Koresheva, T Fujimura, H Azechi, K Mima

JAPANESE JOURNAL OF APPLIED PHYSICS PART 2-LETTERS & EXPRESS LETTERS 45 ( 8-11 ) L335 - L338 2006.3

In this report, we describe fuel (deuterium and tritium) Capsule preparation for the fast-ignition realization experiment (FIREX) in laser fusion research. The required diameter and thickness of the capsule are 500 and 20 pill, respectively. The material Should be plastics with low-density foam. We have prepared such a capsule using (1) a new material of (phloroglucinolcarboxylic acid)/formalin resin to control the kinematic viscosity of the precursor, (2) the phase-transfer-catalyzed gelation process to maintain the density matching of the emulsion. The obtained foam capsule had a fine structure of 180 run (outer surface) to 220 run (inner surface) size and a uniform thickness reaching the resolution limit of optical analysis (similar to 0.5 mu m).

Cool-down performance of the apparatus for the cryogenic target of the FIREX project Reviewed

A. Iwamoto, R. Maekawa, T. Mito, M. Okamoto, O. Motojima, S. Sugito, K. Okada, M. Nakai, T. Norimatsu, K. Nagai

Fusion Engineering and Design 81 ( 8-14 PART B ) 1647 - 1652 2006.2

The apparatus for cryogenic target experiments of the Fast Ignition Realization EXperiment (FIREX) project has been developed at the National Institute for Fusion Science (NIFS). To achieve the target specifications for the project, the foam shell method has been proposed. The Institute of Laser Engineering (ILE), Osaka University and NIFS have started a cooperative study of the method. NIFS is responsible for the demonstration of the fuel layering process. The first cool-down test of the apparatus was conducted. Its cool-down performance is described in this paper. © 2005 Elsevier B.V. All rights reserved.

Angular distribution control of extreme ultraviolet radiation from laser-produced plasma by manipulating the nanostructure of low-density SnO2 targets Reviewed

K Nagai, QC Gu, ZZ Gu, T Okuno, S Fujioka, H Nishimura, YZ Tao, Y Yasuda, M Nakai, T Norimatsu, Y Shimada, M Yamaura, H Yoshida, M Nakatsuka, N Miyanaga, K Nishihara, Y Izawa

APPLIED PHYSICS LETTERS 88 ( 9 ) 2006.2

We have found that the divergence of a relatively monochromatic extreme ultraviolet (EUV) emission from a laser-produced plasma can be manipulated by changing the target morphology which is a porous low-density tin oxide (SnO2) structure. The fundamental light of a Nd-YAG laser was irradiated on the target with laser intensity of similar to 10(11) W/cm(2) and pulse duration of 10 ns. The nanostructure and density of the targets were tuned by a combination of colloidal polymer template and sol-gel processes [Gu, Nagai, Norimatsu, Fujioka, Nishimura, Nishihara, Miyanaga, and Izawa, Chem. Mater. 17, 1115 (2005)], which has a merit in large-scale preparation. When the target has an open cell nanostructure, the EUV emission directed predominantly along target normal, while a closed cell target exhibited divergent emission. The angular distribution may be affected by the orientation of the microstructured initial target, and this phenomenon can be applied to wavefront control of EUV emission.

Ultrafast x-ray imaging with sliced sampling streak cameras Reviewed

TX Huang, M Nakai, H Shiraga, H Azechi, TX Huang, YK Ding, ZJ Zheng

REVIEW OF SCIENTIFIC INSTRUMENTS 77 ( 2 ) 2006.2

Polymorphic tin dioxide synthesis via sol-gel mineralization of ethyl-cyanoethyl cellulose lyotropic liquid crystals Reviewed

Qincui Gu, Keiji Nagai, Mitsuo Nakai, Takayoshi Norimatsu

Colloid and Polymer Science 284 ( 4 ) 429 - 434 2006.1

The polymorphic tin dioxide (SnO2) was synthesized by calcinating the sol-gel mineralized hybrid of the tin source solution (SnC14/ethanol/H2O) and the lyotropic liquid crystal of ethyl-cyanoethyl cellulose((E-CE)C)/acrylic acid (AA). The sub-micrometer SnO2 spheres with bimodal distribution at 370 and 860 nm were obtained after calcinating the hybrid at 400 °C for 5 h. When the hybrid was exposed to ultraviolet first and then calcinated the flying-saucer-like SnO2 was formed. The exposure time was found to influence the morphology of the as-prepared SnO2. Except for the spherical and the flying-saucer-like SnO2, a small amount of well-developed polyhedral SnO2 was also observed in the as-prepared samples. On this basis, the lyotropic liquid crystal of (E-CE)C/AA afforded a novel route to obtain polymorphic SnO2. © Springer-Verlag 2005.

Equation of state of diamond under shock compression up to 2 TPa Reviewed

H. Nagao, K. G. Nakamura, K. Kondo, N. Ozaki, T. Ono, K. Takamatsu, K. A. Tanaka, K. Nagai, M. Nakai, K. Wakabayashi, K. Okada, M. Yoshida

Shock Compression of Condensed Matter - 2005, Pts 1 and 2 845 111 - 114 2006

The equation of state of diamond was studied using laser-driven shock waves in a terapascal region between 0.5 and 2 TPa. Strong shock waves were generated by direct irradiation of a 2.5 ns laser pulse on an Al driver plate. The shock wave velocities in the diamond and Al were measured optically. Particle velocities and pressures were obtained using impedance matching and the known Al Hugoniot. The dependence of U-s(Dia)(u(p)(Dia)) obtained for single crystalline diamond is well-approximated by U-s(Dia)=11.2+1.2u(p)(Dia) for the obtained Hugoniot data, all previous experimental data, and the bulk sound velocity.

Observation of Xenon EUV Spectra in Compact Helical System Reviewed

SUZUKI Chihiro, NISHIMURA Hiroaki, SONG Mi-Young, KATO Takako, OKAMURA Shoichi, MORE Richard, NISHIHARA Katsunobu, NAKAI Mitsuo, SHIGEMORI Keisuke, FUJIOKA Shinsuke, OGAWA Hiroaki, SASAKI Akira

Journal of Plasma and Fusion Research SERIES 7 73 - 76 2006

Towards realization of hyper-velocities for impact fast ignition Reviewed

M. Murakami, H. Nagatomo, T. Sakaiya, H. Azechi, S. Fujioka, H. Shiraga, M. Nakai, K. Shigemori, H. Saito, S. Obenschain, M. Karasik, J. Gardner, J. Bates, D. Colombant, J. Weaver, Y. Aglitskiy

Plasma Physics and Controlled Fusion 47 ( 12 B ) B815 - B822 2005.12

A new ignition scheme, impact fast ignition (IFI), is studied, in which the compressed DT main fuel is to be ignited by impact with another fraction of separately imploded DT fuel, which is accelerated in the hollow conical target. The first and distinct milestone in the IFI scenario is the demonstration of such a hyper-velocity, of the order of 108 cm s-1. Two-dimensional hydrodynamic simulation results obtained in full geometry using plastic instead of DT fuel are presented, in which some key physical parameters for the impact shell dynamics, such as an implosion velocity of 108 cm s-1, a compressed density of 300-400 g cm-3 and a converted temperature greater than 5 keV, are demonstrated. A preliminary experimental result with a planar target is presented to show the highest velocity, 6 × 107 cm s-1, ever achieved. © 2005 IOP Publishing Ltd.

Dynamic imaging of 13.5 nm extreme ultraviolet emission from laser-produced Sn plasmas Reviewed

Y Tao, H Nishimura, T Okuno, S Fujioka, N Ueda, M Nakai, K Nagai, T Norimatsu, N Miyanaga, K Nishihara, Y Izawa

APPLIED PHYSICS LETTERS 87 ( 24 ) 2005.12

Temporally resolved imaging of 13.5 nm extreme ultraviolet (EUV) emission from laser-produced Sn plasmas was experimentally investigated with a monochromatic EUV imager. Absorption caused by the surrounding plasma was eliminated by adopting a stripe Sn target laminated on a plastic film so that the CH plasma tamped lateral expansion of the Sn plasma. The experimental results revealed that reabsorption induced by plasma, both in EUV emission-dominant and long scale coronal regions, plays an key role in extracting the EUV light from the plasma efficiently. (c) 2005 American Institute of Physics.

Opacity effect on extreme ultraviolet radiation from laser-produced tin plasmas Reviewed

S Fujioka, H Nishimura, K Nishihara, A Sasaki, A Sunahara, T Okuno, N Ueda, T Ando, YZ Tao, Y Shimada, K Hashimoto, M Yamaura, K Shigemori, M Nakai, K Nagai, T Norimatsu, T Nishikawa, N Miyanaga, Y Izawa, K Mima

PHYSICAL REVIEW LETTERS 95 ( 23 ) 2005.12

Opacity effects on extreme ultraviolet (EUV) emission from laser-produced tin (Sn) plasma have been experimentally investigated. An absorption spectrum of a uniform Sn plasma generated by thermal x rays has been measured in the EUV range (9-19 nm wavelength) for the first time. Experimental results indicate that control of the optical depth of the laser-produced Sn plasma is essential for obtaining high conversion to 13.5 nm-wavelength EUV radiation; 1.8% of the conversion efficiency was attained with the use of 2.2 ns laser pulses.

Resorcinol-formalin foam balls via gelation of emulsion using phase-transfer catalysts Reviewed

Fuyumi Ito, Keiji Nagai, Mitsuo Nakai, Takayoshi Norimatsu

Macromolecular Chemistry and Physics 206 ( 21 ) 2171 - 2176 2005.11

Highly spherical (98.5%) low-density foam balls with 1-mm diameters were fabricated from a density-matched emulsion consisting of a resorcinol/formalin aqueous solution and a (mineral oil and carbon tetrachloride) mixture. Phase-transfer catalysts of carboxylic acid were utilized to induce gelation of the emulsion. The gelation process was monitored by a mechanical test. Gelation forming ball shapes happened within 20-30 min, depending on the catalysts, at room temperature. The gelation time decreased with high-catalyst concentration. Acids with long alkyl chains did not induce gelation and no balls were obtained. The gelated balls were dried to obtain foam via an exchange of the solvent with 2-propanol and extraction using the supercritical fluid CO2. The density obtained from the catalyst was 0.15-0.16 g · cm-3. SEM images revealed surface membrane formation, which can be explained by local concentration at the interface of W/O. We observed different bulk foam cell sizes, which may depend on the catalysts and, therefore, on the different gelation rates. © 2005 WILEY-VCH Verlag GmbH &amp
Co. KGaA, Weinheim.

Foam materials for cryogenic targets of fast ignition realization experiment (FIREX) Reviewed

K Nagai, H Azechi, F Ito, A Iwamoto, Y Izawa, T Johzaki, R Kodama, K Mima, T Mito, M Nakai, N Nemoto, T Norimatsu, Y Ono, K Shigemori, H Shiraga, KA Tanaka

NUCLEAR FUSION 45 ( 11 ) 1277 - 1283 2005.11

Development of foam materials for cryogenically cooled fuel targets is described in this paper. The fabrication development was initiated as a part of the fast ignition realization experiment (FIREX) project at the ILE, Osaka University under a bilateral collaboration between OsakaUniversity and National Institute for Fusion Science (NIFS). For the first stage of FIREX (FIREX-1), a foam cryogenic target was designed in which low-density foam shells with a conical light guide will be fuelled through a narrow pipe and will be cooled down to the cryogenic temperature. Acrylic polymer, resorcinol-formaldehyde (RF) resin, poly(4-methyl-1-pentene) (PMP), and polystyrene-based crosslinking polymer have been investigated as supporting materials for cryogenic fuel. The properties of the material and the present status of the material development are summarized.

Characterization of density profile of laser-produced Sn plasma for 13.5 nm extreme ultraviolet source Reviewed

Y Tao, H Nishimura, S Fujioka, A Sunahara, M Nakai, T Okuno, N Ueda, K Nishihara, N Miyanaga, Y Izawa

APPLIED PHYSICS LETTERS 86 ( 20 ) 2005.5

We investigated the electron density profile corresponding to the dominant extreme ultraviolet (EUV) emission from a laser-produced Sn plasma using a combination of a green and an UV interferometer. A comparison between experimental results and a one-dimensional radiation hydrodynamic simulation shows reasonable agreement, and the discrepancy could be attributed to three-dimensional plasma expansion. It was found that, due to opacity effects, most of the EUV light comes from an under-dense plasma region. (c) 2005 American Institute of Physics.

Present status of fast ignition research and prospects of FIREX project Reviewed

K Mima, H Azechi, Y Johzaki, Y Kitagawa, R Kodama, Y Kozaki, N Miyanaga, K Nagai, H Nagatomo, M Nakai, H Nishimura, T Norimatsu, H Shiraga, KA Tanaka, Y Izawa, Y Nakao, H Sakagami

FUSION SCIENCE AND TECHNOLOGY 47 ( 3 ) 662 - 666 2005.4

This is the review on the laser fusion research at Institute of Laser Engineering of Osaka University. Since 1996, we have concentrated our efforts on fast ignition laser fusion research. By constructing 100 TW and 1 Peta watt lasers, experiments on relativistic laser plasma interactions related to fast ignition and pellet implosion and heating have been carried out. The results indicate that imploded core plasma is heated with relatively high coupling efficiency. According to the above results, we started the FIREX (Fast Ignition Realization Experiment) project for demonstrating ignition and burn with a multi 10kJ short pulse laser. The future prospects of the project are presented in this paper.

　 PREV - NEXT 　

<Nakai Mitsuo>

Papers - Nakai Mitsuo