Faculty Profiles - Nakai Mitsuo

Papers - Nakai Mitsuo

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Quantitative K alpha line spectroscopy for energy transport in ultra-intense laser plasma interaction Reviewed

Z. Zhang, H. Nishimura, S. Fujioka, Y. Arikawa, M. Nakai, H. Chen, J. Park, G. J. Williams, T. Ozaki, H. Shiraga, S. Kojima, T. Johzaki, A. Sunahara, N. Miyanaga, J. Kawanaka, Y. Nakata, T. Jitsuno, H. Azechi

8TH INTERNATIONAL CONFERENCE ON INERTIAL FUSION SCIENCES AND APPLICATIONS (IFSA 2013) 688 2016

Absolute Ka line spectroscopy is proposed for studying laser-plasma interactions taking place in the cone-guided fast ignition targets. X-ray spectra ranging from 20 to 100 keV were quantitatively measured with a Laue spectrometer. The absolute sensitivities of the Laue spectrometer system were calibrated using pre-characterized laser-produced x-ray sources and radioisotopes. The integrated reflectivity for the crystal is in good agreement with predictions by an open code for x-ray diffraction. The energy transfer efficiency from incident laser beams to hot electrons, as the energy transfer agency, is derived as a consequence of this work. The absolute yield of Au and Ta Ka lines were measured in the fast ignition experimental campaign performed at Institute of Laser Engineering, Osaka University. Applying the hot electron spectrum information from the electron spectrometer, an energy transfer efficiency of the incident LFEX [1], a kJ-class PW laser, to hot electrons was derived for a planar and cone-guided geometry.

The diagnostics of the energy coupling efficiency in the Fast Ignition integrated experiment Reviewed

Y. Arikawa, S. Fujioka, A. Morace, Z. Zhang, T. Nagai, M. Taga, Y. Abe, S. Kojima, S. Sakata, H. Inoue, M. Utsugi, S. Hattori, S. H. Lee, T. Ikenouchi, T. Hosoda, A. Sunahara, T. Ozaki, T. Johzaki, H. Nagatomo, K. Yamanoi, T. Shimizu, S. Tokita, Y. Fujimoto, J. Kawanaka, Y. Nakata, M. Nakai, H. Shiraga, H. Jitsuno, N. Sarukura, N. Miyanaga, T. Norimatsu, H. Nishimura, H. Azechi

8TH INTERNATIONAL CONFERENCE ON INERTIAL FUSION SCIENCES AND APPLICATIONS (IFSA 2013) 688 2016

The energy coupling efficiency (CE) in Fast Ignition (FI) laser fusion was studied at GEKKO XII and LFEX laser facility by using newly developed targets and plasma diagnostic instruments. The gated-liquid scintillator neutron detectors had been upgraded by using neutron collimators for intense background fluxes of gamma-rays and neutrons in the FI experiment. Clear fusion neutron signal was successfully recorded in the sub-kJ heating FI experiment. Up to 5 times neutron yield enhancement was observed, and the CE of the heating laser to core plasma was estimated to be 1.6 % for cone-in-shell target implosion by 9 beams and core heating by LFEX pulse 115 ps before bang time. The laser-to-electron energy conversion efficiency was separately diagnosed using a newly developed target and resulted to be 45 %. The fast electron energy spectrum was estimated to be 2.3 MeV slope temperature by hard x-ray spectroscopy. Monte Carlo simulations demonstrate the consistency of the data set.

Time evolution of the diamond surface shape due to non-uniform laser irradiation

Kato H., Shigemori K., Ueda T., Nagatomo H., Sakaiya T., Terasaki H., Hironaka Y., Nakai M., Azechi H.

Meeting Abstracts of the Physical Society of Japan 71 583 - 583 2016

Heating efficiency evaluation with mimicking plasma conditions of integrated fast-ignition experiment Reviewed

Shinsuke Fujioka, Tomoyuki Johzaki, Yasunobu Arikawa, Zhe Zhang, Alessio Morace, Takahito Ikenouchi, Tetsuo Ozaki, Takahiro Nagai, Yuki Abe, Sadaoki Kojima, Shohei Sakata, Hiroaki Inoue, Masaru Utsugi, Shoji Hattori, Tatsuya Hosoda, Seung Ho Lee, Keisuke Shigemori, Youichiro Hironaka, Atsushi Sunahara, Hitoshi Sakagami, Kunioki Mima, Yasushi Fujimoto, Kohei Yamanoi, Takayoshi Norimatsu, Shigeki Tokita, Yoshiki Nakata, Junji Kawanaka, Takahisa Jitsuno, Noriaki Miyanaga, Mitsuo Nakai, Hiroaki Nishimura, Hiroyuki Shiraga, Hideo Nagatomo, Hiroshi Azechi

PHYSICAL REVIEW E 91 ( 6 ) 2015.6

A series of experiments were carried out to evaluate the energy-coupling efficiency from heating laser to a fuel core in the fast-ignition scheme of laser-driven inertial confinement fusion. Although the efficiency is determined by a wide variety of complex physics, from intense laser plasma interactions to the properties of high-energy density plasmas and the transport of relativistic electron beams (REB), here we simplify the physics by breaking down the efficiency into three measurable parameters: (i) energy conversion ratio from laser to REB, (ii) probability of collision between the REB and the fusion fuel core, and (iii) fraction of energy deposited in the fuel core from the REB. These three parameters were measured with the newly developed experimental platform designed for mimicking the plasma conditions of a realistic integrated fast-ignition experiment. The experimental results indicate that the high-energy tail of REB must be suppressed to heat the fuel core efficiently.

Quantitative K alpha line spectroscopy for energytransport in fast ignition plasma driven with LFEX PW laser Reviewed

Z. Zhang, H. Nishimura, S. Fujioka, Y. Arikawa, T. Ikenouchi, M. Nakai, H. Nagatomo, H. Chen, J. Park, G. J. Williams, T. Ozaki, H. Shiraga, S. Kojima, H. Hosoda, N. Miyanaga, J. Kawanaka, Y. Nakata, T. Jitsuno, H. Azechi

HIGH ENERGY DENSITY PHYSICS 15 78 - 81 2015.6

Quantitative high-energy X-ray spectroscopy is applied for the laser plasma interaction in the fast ignition scheme. A double tracer layer target is designed for the absolute measurement of hot electron temperature and laser energy transfer efficiency. The hot electron temperature is determined from the ratio of the number of K alpha photons from the first and second tracers. Consequently, the energy transfer efficiency from incident laser beams to hot electrons, as the energy transfer mechanism, is derived. In a cone-guide geometry, we simultaneously measured the hot electron temperature and the energy transfer efficiency from the incident LFEX, a kJ-class PW laser, which were measured to be 5.3 MeV and 37%, respectively. (C) 2015 Elsevier B.V. All rights reserved.

Response measurement of single-crystal chemical vapor deposition diamond radiation detector for intense X-rays aiming at neutron bang-time and neutron burn-history measurement on an inertial confinement fusion with fast ignition Reviewed

T. Shimaoka, J. H. Kaneko, Y. Arikawa, M. Isobe, Y. Sato, M. Tsubota, T. Nagai, S. Kojima, Y. Abe, S. Sakata, S. Fujioka, M. Nakai, H. Shiraga, H. Azechi, A. Chayahara, H. Umezawa, S. Shikata

REVIEW OF SCIENTIFIC INSTRUMENTS 86 ( 5 ) 2015.5

A neutron bang time and burn history monitor in inertial confinement fusion with fast ignition are necessary for plasma diagnostics. In the FIREX project, however, no detector attained those capabilities because high-intensity X-rays accompanied fast electrons used for plasma heating. To solve this problem, single-crystal CVD diamond was grown and fabricated into a radiation detector. The detector, which had excellent charge transportation property, was tested to obtain a response function for intense X-rays. The applicability for neutron bang time and burn history monitor was verified experimentally. Charge collection efficiency of 99.5% +/- 0.8% and 97.1% +/- 1.4% for holes and electrons were obtained using 5.486 MeV alpha particles. The drift velocity at electric field which saturates charge collection efficiency was 1.1 +/- 0.4 x 10(7) cm/s and 1.0 +/- 0.3 x 10(7) cm/s for holes and electrons. Fast response of several ns pulse width for intense X-ray was obtained at the GEKKO XII experiment, which is sufficiently fast for ToF measurements to obtain a neutron signal separately from X-rays. Based on these results, we confirmed that the single-crystal CVD diamond detector obtained neutron signal with good S/N under ion temperature 0.5-1 keV and neutron yield of more than 109 neutrons/shot. (C) 2015 AIP Publishing LLC.

18pCP-10 Effects of material response due to compressibility on laser imprinting

Kato H., Shigemori K., Nakai M., Sakaiya T., Hosogi R., Terasaki H., Nagatomo H., Hironaka Y., Azechi H.

Meeting Abstracts of the Physical Society of Japan 70 679 - 679 2015

24aBH-3 Theory and ignition taget design of fast ignition with irradiation on the inner surface of the

Sunahara A., Johzaki T., Yanagawa T., Sakagami H., Abe Y., Nagai T., Lee S., Zhe Zhang, Ikenouchi T., Kojima S., Sakata S., Arikawa Y., Fujioka S., Nakai M., Shiraga H., Norimatsu T., Azechi H., FIREX project team

Meeting Abstracts of the Physical Society of Japan 70 925 - 925 2015

22aCM-6 Study of Proton Stopping Power in Dense Plasmas

Morace A., Feugeas J-L., Nicolai P., Fujioka S., Arikawa Y., Norimatsu T., Hosokawa H., Honrubia J., Batani D., Jakubowska K., Yogo A., Nakai M., Kojima S., Zhang Z., Abe Y., Mima K., Shiraga H., Nishimura H., Azechi H.

Meeting Abstracts of the Physical Society of Japan 70 861 - 861 2015

19aCP-5 The influence on the fast electron generation from implosion plasma Reviewed

Arikawa Y., Gawa T., Yamamoto T., Matsuo K., Tosaki S., L.K. Fai, Kawashima T., Ueda T., Hironaka Y., Sigemori K., Yogo A., Kojima S., Miyanaga N., Jitsuno T., Kawanaka J., Nakata Y., Tokita S., Nagatomo H., Nihsimura H., Shiraga H., Nakai M., Sunahara A., Fujioka S., Johzaki T., Ozaki T., Sakagami H., Z. Zhang, Azechi H., FIREX group, LFEX group, Alessio M., Hata M., Sakata S., Abe Y., Lee S. H., Kato H.

Meeting Abstracts of the Physical Society of Japan 70 ( 0 ) 698 - 698 2015

19aCP-2 Experimental Study of Transport of Relativistic Electron Beams in Strong Magnetic Mirror Field Reviewed

Sakata S., Arikawa Y., M. Bailly-Grandvaux, C. Bellei, Ozaki T., Hata M., Johzaki T., Sunahara A., Yogo Y., Nakai M., Nishimura H., Kondo K., Shiraga H., Nagatomo H., J. J. Santos, Fujioka S., Azechi H., Hironaka Y., Kojima S., Matsuo K., K. F. Law, S. H. Lee, A. Morace, X. Vaisseau

Meeting Abstracts of the Physical Society of Japan 70 ( 0 ) 695 - 695 2015

24pBH-6 Electron generation experiment for fast ignition using plasma mirror

Arikawa Y., Kojima S., Fujioka S., Morace Alessio, Gawa T., Sakata S., Yogo A., Zhe Zhang, Tokita S., Ikenouchi T., Nagai T., Abe Y., Utsugi M., Lee S. H., Inoue H., Taguchi Y., Matsuo K., Tosaki S., Hata M., Nagatomo H., Sunahara A., Johzaki T., Ozaki T., Sakagami H., Inoue S., Teramoto K., Nakashima Y., Hashida M., Sakabe S., Sagisaka A., Ogura K., Pirozhkov Alexander, Nishikino M., Kondo K., Nishimura H., Shiraga H., Nakai M., FIREX group, LFEX group, Azechi H.

Meeting Abstracts of the Physical Society of Japan 70 953 - 953 2015

High-intensity neutron generation via laser-driven photonuclear reaction Invited

Yasunobu Arikawa, Masaru Utsugi, Morace Alessio, Takahiro Nagai, Yuki Abe, Sadaoki Kojima, Shohei Sakata, Hiroaki Inoue, Shinsuke Fujioka, Zhe Zhang, Hui Chen, Jaebum Park, Jackson Williams, Taichi Morita, Yoichi Sakawa, Yoshiki Nakata, Junji Kawanaka, Takahisa Jitsuno, Nobuhiko Sarukura, Noriaki Miyanaga, Mitsuo Nakai, Hiroyuki Shiraga, Hiroaki Nishimura, Hiroshi Azechi

Plasma and Fusion Research 10 ( SpecialIssue.1 ) 2015 2015

© 2015 The Japan Society of Plasma Science and Nuclear Fusion Research. The generation of high-peak-intensity neutrons through a photonuclear reaction was demonstrated using the Laser for Fast Ignition Experiments (LFEX) at Osaka University. Up to 109 neutrons/shot were generated from a 1mm sized gold target. Using Monte Carlo simulations, the neutron spectrum from keV to MeV was found to be independent of the γ-ray spectrum. The typical peak neutron intensity of 1021 neutrons /cm2/s at the target surface was estimated, and it should be a useful tool for nuclear synthesis experiments.

Laser erosion diagnostics of plasma facing materials with displacement sensors and their application to safeguard monitors to protect nuclear fusion chambers Reviewed

Koichi Kasuya, Shinji Motokoshi, Seiji Taniguchi, Mitsuo Nakai, Kazutoshi Tokunaga, Waldemar Mroz, Bogus Law Budner, Barbara Korczyc

XX INTERNATIONAL SYMPOSIUM ON HIGH-POWER LASER SYSTEMS AND APPLICATIONS 2014 9255 2015

Tungsten and SiC are candidates for the structural materials of the nuclear fusion reactor walls, while CVD poly-crystal diamond is candidate for the window material under the hazardous fusion stresses. We measured the surface endurance strength of such materials with commercial displacement sensors and our recent evaluation method. The pulsed high thermal input was put into the material surfaces by UV lasers, and the surface erosions were diagnosed. With the increase of the total number of the laser shots per position, the crater depth increased gradually. The 3D and 2D pictures of the craters were gathered and compared under various experimental conditions. For example, the maximum crater depths were plotted as a function of shot accumulated numbers, from which we evaluated the threshold thermal input for the surface erosions to be induced. The simple comparison-result showed that tungsten was stronger roughly two times than SiC. Then we proposed how to monitor the surface conditions of combined samples with such diamonds coated with thin tungsten layers, when we use such samples as parts of divertor inner walls, fusion chamber first walls, and various diagnostic windows. We investigated how we might be able to measure the inner surface erosions with the same kinds of displacement sensors. We found out the measurable maximum thickness of such diamond which is useful to monitor the erosion. Additionally we showed a new scheme of fusion reactor systems with injectors for anisotropic pellets and heating lasers under the probable use of W and/or SiC.

Characterizing a fast-response, low-afterglow liquid scintillator for neutron time-of-flight diagnostics in fast ignition experiments Reviewed

Y. Abe, H. Hosoda, Y. Arikawa, T. Nagai, S. Kojima, S. Sakata, H. Inoue, Y. Iwasa, K. Iwano, K. Yamanoi, S. Fujioka, M. Nakai, N. Sarukura, H. Shiraga, T. Norimatsu, H. Azechi

REVIEW OF SCIENTIFIC INSTRUMENTS 85 ( 11 ) 1.10E+127 2014.11

The characteristics of oxygen-enriched liquid scintillators with very low afterglow are investigated and optimized for application to a single-hit neutron spectrometer for fast ignition experiments. It is found that 1,2,4-trimethylbenzene has better characteristics as a liquid scintillator solvent than the conventional solvent, p-xylene. In addition, a benzophenon-doped BBQ liquid scintillator is shown to demonstrate very rapid time response, and therefore has potential for further use in neutron diagnostics with fast time resolution. (C) 2014 AIP Publishing LLC.

Development of multichannel low-energy neutron spectrometer Reviewed

Y. Arikawa, T. Nagai, Y. Abe, S. Kojima, S. Sakata, H. Inoue, M. Utsugi, Y. Iwasa, T. Murata, N. Sarukura, M. Nakai, H. Shiraga, S. Fujioka, H. Azechi

REVIEW OF SCIENTIFIC INSTRUMENTS 85 ( 11 ) 2014.11

A multichannel low-energy neutron spectrometer for down-scattered neutron (DSN) measurements in inertial confinement fusion (ICF) experiments has been developed. Our compact-size 256-channel lithium-glass-scintillator-based spectrometer has been implemented and tested in ICF experiments with the GEKKO XII laser. We have performed time calibration of the 256-channel analog-to-digital convertor system used for DSN measurements via X-ray pulse signals. We have clearly observed the DD-primary fusion neutron signal and have successfully studied the detector's impulse response. Our detector is soon to be implemented in future ICF experiments. (C) 2014 AIP Publishing LLC.

Accuracy evaluation of a Compton X-ray spectrometer with bremsstrahlung X-rays generated by a 6 MeV electron bunch Reviewed

Sadaoki Kojima, Yasunobu Arikawa, Yasuhiko Nishimura, Hiromi Togawa, Zhe Zhang, Takahito Ikenouchi, Tetsuo Ozaki, Alessio Morace, Takahiro Nagai, Yuki Abe, Shouhei Sakata, Hiroaki Inoue, Masaru Utsugi, Mitsuo Nakai, Hiroaki Nishimura, Hiroyuki Shiraga, Ryukou Kato, Shinsuke Fujioka, Hiroshi Azechi

REVIEW OF SCIENTIFIC INSTRUMENTS 85 ( 11 ) 2014.11

A Compton-scattering-based X-ray spectrometer is developed to obtain the energy distribution of fast electrons produced by intense laser and matter interactions. Bremsstrahlung X-rays generated by fast electrons in a material are used to measure fast electrons' energy distribution in matter. In the Compton X-ray spectrometer, X-rays are converted into recoil electrons by Compton scattering in a converter made from fused silica glass, and a magnet-based electron energy analyzer is used to measure the energy distribution of the electrons that recoil in the direction of the incident X-rays. The spectrum of the incident X-rays is reconstructed from the energy distribution of the recoil electrons. The accuracy of this spectrometer is evaluated using a quasi-monoenergetic 6 MeV electron bunch that emanates from a linear accelerator. An electron bunch is injected into a 1.5 mm thick tungsten plate to produce bremsstrahlung X-rays. The spectrum of these bremsstrahlung X-rays is obtained in the range from 1 to 9MeV. The energy of the electrons in the bunch is estimated using a Monte Carlo simulation of particle-matter interactions. The result shows that the spectrometer's energy accuracy is +/- 0.5 MeV for 6.0 MeV electrons. (C) 2014 AIP Publishing LLC.

Photonuclear reaction based high-energy x-ray spectrometer to cover from 2 MeV to 20 MeV Reviewed

S. Sakata, Y. Arikawa, S. Kojima, T. Ikenouchi, T. Nagai, Y. Abe, H. Inoue, A. Morace, M. Utsugi, R. Kato, H. Nishimura, M. Nakai, H. Shiraga, S. Fujioka, H. Azechi

REVIEW OF SCIENTIFIC INSTRUMENTS 85 ( 11 ) 2014.11

A photonuclear-reaction-based hard x-ray spectrometer is developed to measure the number and energy spectrum of fast electrons generated by interactions between plasma and intense laser light. In this spectrometer, x-rays are converted to neutrons through photonuclear reactions, and the neutrons are counted with a bubble detector that is insensitive to x-rays. The spectrometer consists of a bundle of hard x-ray detectors that respond to different photon-energy ranges. Proof-of-principle experiment was performed on a linear accelerator facility. A quasi-monoenergetic electron bunch (N-e = 1.0 x 10(-6) C, E-e = 16 +/- 0.32 MeV) was injected into a 5-mm-thick lead plate. Bremsstrahlung x-rays, which emanate from the lead plate, were measured with the spectrometer. The measured spectral shape and intensity agree fairly well with those computed with a Monte Carlo simulation code. The result shows that high-energy x-rays can be measured absolutely with a photon-counting accuracy of 50%-70% in the energy range from 2 MeV to 20 MeV with a spectral resolution (Delta h nu/h nu) of about 15%. Quantum efficiency of this spectrometer was designed to be 10(-7), 10(-4), 10(-5), respectively, for 2-10, 11-15, and 15-25 MeV of photon energy ranges. (C) 2014 AIP Publishing LLC.

Development of x-ray radiography for high energy density physics Reviewed

A. Morace, L. Fedeli, D. Batani, S. Baton, F. N. Beg, S. Hulin, L. C. Jarrott, A. Margarit, M. Nakai, M. Nakatsutsumi, P. Nicolai, N. Piovella, M. S. Wei, X. Vaisseau, L. Volpe, J. J. Santos

PHYSICS OF PLASMAS 21 ( 10 ) 2014.10

We describe an experiment performed at the LULI laser facility using an advanced radiographic technique that allowed obtaining 2D, spatially resolved images of a shocked buried-code-target. The technique is suitable for applications on Fast Ignition as well as Warm Dense Matter research. In our experiment, it allowed to show cone survival up to Mbar pressures and to measure the shock front velocity and the fluid velocity associated to the laser-generated shock. This allowed obtaining one point on the shock polar of porous carbon. (C) 2014 AIP Publishing LLC.

High intensity g-ray and neutron generation by ultra intense laser Reviewed

Yasunobu Arikawa, Masaru Utsugi, Alessio Morace, Takahiro Nagai, Sadaoki Kojima, Shohei Sakata, Hiroaki Inoue, Shigeki Tokita, Yoshiki Nakata, Junji Kawanaka, Takahisa Jitsuno, Nobuhiko Sarukura, Noriaki Miyanaga, Mitsuo Nakai, Hiroyuki Shiraga, Hiroaki Nishimura, Hiroshi Azechi

ABSTRACTS OF PAPERS OF THE AMERICAN CHEMICAL SOCIETY 248 2014.8

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Papers - Nakai Mitsuo