Faculty Profiles - Nakai Mitsuo

Papers - Nakai Mitsuo

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Stabilization of radiation reaction with vacuum polarization Reviewed

Keita Seto, Sen Zhang, James Koga, Hideo Nagatomo, Mitsuo Nakai, Kunioki Mima

PROGRESS OF THEORETICAL AND EXPERIMENTAL PHYSICS ( 4 ) 2014.4

From the development of the electron theory by H. A. Lorentz in 1906, many authors have tried to reformulate this model. P. A. M. Dirac derived the relativistic-classical electron model in 1938, which is now called the Lorentz-Abraham-Dirac model. But this model has the big difficulty of the runaway solution. Recently, this equation has become important for ultra-intense laser-electron (plasma) interactions. For simulations in this research field, it is desirable to stabilize this model of the radiation reaction. In this paper, we will discuss this ability for radiation reaction with the inclusion of vacuum polarization.

Development of compton X-ray spectrometer for fast ignition experiment Reviewed

Sadaoki Kojima, Yasunobu Arikawa, Takahito Ikenouchi, Takahiro Nagai, Yuki Abe, Shouhei Sakata, Hiroaki Inoue, Takuya Namimoto, Shinsuke Fujioka, Mitsuo Nakai, Hiroyuki Shiraga, Tetsuo Ozaki, Makoto R. Asakawa, Ryukou Kato, Hiroshi Azechi

Plasma and Fusion Research 9 ( 3 ) 2014

In the context of Fast Ignition, the fast electron temperature is a key parameter to determine the laserto- fast electron energy conversion efficiency. Bremsstrahlung X-ray (γ-ray) emission represents an attractive alternative to measure this fundamental parameter. In this study, a single-shot high-energy γ-ray spectrometer with sensitivity ranging from 0.5MeV to 7MeV was developed, allowing to estimate the γ-ray spectrum in the fast ignition. © 2014 The Japan Society of Plasma Science and Nuclear Fusion Research.

Energy transportation by mev hot electrons in fast ignition plasma driven with LFEX PW laser Reviewed

Zhe Zhang, Hiroaki Nishimura, Shinsuke Fujioka, Yasunobu Arikawa, Mitsuo Nakai, Hideo Nagatomo, Hiroyuki Shiraga, Sadaoki Kojima, Alessio Morace, Noriaki Miyanaga, Junji Kawanaka, Yoshiki Nakata, Takahisa Jitsuno, Hiroshi Azechi, Tetsuo Ozaki, Hui Chen, Jaebum Park, Gerald Jackson Williams, Tomoyuki Johzaki, Atsushi Sunahara

Plasma and Fusion Research 9 2014

Implosion and heating experiments with the scheme of fast ignition (FI) have been performed on Gekko-XII and LFEX laser platform at the Institute of Laser Engineering in Osaka University. A cone-guided CD-shell has been used as a base-line target for the fast ignition realization. The information about energy transfer from LFEX petawatt (PW) laser is quantitatively studied with an absolute Kα diagnostics and a fast electron trajectory simulation. The transfer efficiency (ηTE) is estimated for a planar interaction as a reference and for several types of guiding-cone. As a general trend, the guiding-cone enhanced the ηTE by a factor of 3 comparing with the planar case.

The development of the neutron detector for the fast ignition experiment by using LFEX and gekko XII facility Reviewed

Nagai T, Nakai M, Arikawa Y, Abe Y, Kojima S, Sakata S, Inoue H, Fujioka S, Shiraga H, Sarukura N, Norimatsu T, Azechi H

Plasma and Fusion Research 9 ( SPECIALISSUE.3 ) 2014

The neutron imaging diagnostics and reconstructing technique for fast ignition Reviewed

Inoue H, Arikawa Y, Nozaki S, Fujioka S, Nagai T, Kojima S, Abe Y, Sakata S, Kinjo A, Nakai M, Shiraga H, Azechi H

Plasma and Fusion Research 9 ( SPECIALISSUE.3 ) 2014

Present status of fast ignition realization experiment and inertial fusion energy development Reviewed

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

NUCLEAR FUSION 53 ( 10 ) 2013.10

One of the most advanced fast ignition programmes is the fast ignition realization experiment (FIREX). The goal of its first phase is to demonstrate ignition temperature of 5 keV, followed by the second phase to demonstrate ignition-and-burn. The second series experiment of FIREX-I, from late 2010 to early 2011, has demonstrated a high (>10%) coupling efficiency from laser to thermal energy of the compressed core, suggesting that the ignition temperature can be achieved at laser energy below 10 kJ. Further improvement of the coupling efficiency is expected by introducing laser-driven magnetic fields.

Luminescence properties of Nd3+ and Er3+ doped glasses in the VUV region Reviewed

Kohei Yamanoi, Takahiro Murata, Yasunobu Arikawa, Tomoharu Nakazato, Marilou Cadatal-Raduban, Toshihiko Shimizu, Nobuhiko Sarukura, Mitsuo Nakai, Takayoshi Norimatsu, Hiroaki Nishimura, Hiroshi Azechi, Shigeru Fujino, Hideki Yoshida, Akira Yoshikawa, Nakahiro Satoh, Hirofumi Kan

OPTICAL MATERIALS 35 ( 11 ) 1962 - 1964 2013.9

We report the vacuum ultraviolet (VUV) spectroscopy of APLF + Nd and APLF + Er glass, with composition 20Al(PO3)(3)-80LiF + 1NdF(3) and + 1ErF(3) (in mol%). APLF + Nd and APLF + Er have a dominant fluorescence peak at 185 nm and 168 nm with decay times of 4.5 ns and 5.8 ns, respectively. Fluorescence from APLF + Nd is attributed to 4f(2)5d -> 4f(3) transitions in neodymium (Nd) while fluorescence from APLF + Er is due to spin allowed transition in erbium (Er). This is the first report of VUV fluorescence from rare earth ions doped in glass hosts, which could provide the basis for mass production of VUV emitting materials. Our results also suggest the potential of using APLF + Nd and APLF + Er as neutron scintillators during inertial confinement fusion. (C) 2012 Elsevier B.V. All rights reserved.

Quantitative measurement of hard X-ray spectra from laser-driven fast ignition plasma Reviewed

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

High Energy Density Physics 9 ( 3 ) 435 - 438 2013.9

Absolute K. α line spectroscopy is proposed for studying laser-plasma interactions taking place in the Au cone-guided fast ignition targets. X-ray spectra ranging from 20 to 100keV were quantitatively measured with a Laue spectrometer composed of a cylindrically curved crystal and a filter-absorption method for Bremsstrahlung continuum emission. The absolute sensitivities of the Laue spectrometer systems 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 X-ray diffraction code. The energy transfer efficiency from incident laser beams to hot electrons, as the energy transfer mechanism, is derived from this work. The absolute yield of Au and Ta K. α lines were measured in the fast ignition experimental campaign performed at Institute of Laser Engineering, Osaka University. Applying the hot electron spectrum information from electron spectrometer and scaling laws, the energy transfer efficiency from the incident LFEX, a kJ-class PW laser, to hot electrons was derived for the first time. © 2013 Elsevier B.V.

FIREX foam cryogenic target development: Residual void reduction and estimation with solid hydrogen refractive index measurements Reviewed

A. Iwamoto, T. Fujimura, M. Nakai, T. Norimatsu, H. Sakagami, H. Shiraga, H. Azechi

Nuclear Fusion 53 ( 8 ) 2013.8

Voidless fuel solidification within a foam material is attempted for the development of a Fast Ignition Realization EXperiment (FIREX) target. A typical target consists of a foam shell with a thin solid fuel layer, a gold cone guide and a glass fill tube. The foam layer is formed with aggregations of tiny cells. The porous foam material has the advantage of forming a uniform layer in a liquid state by the effect of capillarity. Random liquid-solid transitions of fuel, however, would cause void spaces in each cell because of their different densities. To form a voidless solid fuel layer in the FIREX target, we propose a layering method, which includes the process of controlled solidification and simultaneous liquid fuel supply to the liquid/solid interface. Normal H 2 is used as a surrogate fuel for our experiments. By applying a resorcinol/formalin aerogel, which has been developed in the Institute of Laser Engineering, Osaka University, instead of a foam material, formation of a solid H2 layer with reduced void spaces is preliminarily demonstrated. Related solid H2 refractive indices are measured to estimate the void fraction. Eventually, its filling factor reaches ∼99%. Furthermore, the application of the proved method is numerically simulated on the FIREX target. The method is confirmed to be applicable in it with a cone guide heating technique. © 2013 IAEA, Vienna.

Report on OPIC Conference on Laser and Accelerator Neutron Sources and Applications '13 (LANSA '13)

NISHIMURA Hiroaki, ARIKAWA Yasunobu, NAKAI Mitsuo

41 ( 7 ) 540 - 542 2013.7

Electronic States of Trivalent Praseodymium Ion Doped in 20Al(PO3)(3)-80LiF Glass Reviewed

Tsuboi Mizuki, Takeda Kohei, Nakazato Tomoharu, Kono Masahiro, Yamanoi Kohei, Cadatal-Raduban Marilou, Sakai Kohei, Nishi Ryosuke, Minami Yuki, Mui Viet Luong, Arikawa Yasunobu, Shimizu Toshihiko, Sarukurua Nobuhiko, Norimatsu Takayoshi, Nakai Mitsuo, Azechi Hiroshi, Murata Takahiro, Fujino Shigeru, Yoshida Hideki, Yoshikawa Akira, Sato Nakahiro, Kan Hirofumi, Kamata Kei

JAPANESE JOURNAL OF APPLIED PHYSICS 52 ( 6 ) 2013.6

We investigate the photoluminescence (PL) and photoluminescence excitation (PLE) spectra of 20Al(PO3)(3)-80LiF+Pr glass (APLF+Pr) and Pr3+-doped LiCaAlF6 crystal (Pr:LiCAF) in order to determine the electronic states of Pr3+ in APLF glass host and to improve APLF+Pr scintillation properties. Ultraviolet (UV) emission bands at around 250 and 340nm were observed from both materials and these can be ascribed to 4f5d -> 4f(2) transitions in Pr3+. Emission at around 400nm was also obtained and is principally attributed to S-1(0) -> 4f(2) transition. Difference in the emission profiles of these two materials was found to be due to the extent of the 5d band and its position relative to the S-1(0) state. Increasing the concentration of Pr3+ up to 2 mol% was found to improve UV emission ratio due to the faster cross-relaxation of 4f states. This could improve the quantum efficiency of APLF+Pr as a neutron scintillator for scattered-neutron diagnostics in laser fusion research. (C) 2013 The Japan Society of Applied Physics

New insights into the laser produced electron-positron pairs Reviewed

Hui Chen, M. Nakai, Y. Sentoku, Y. Arikawa, H. Azechi, S. Fujioka, C. Keane, S. Kojima, W. Goldstein, B. R. Maddox, N. Miyanaga, T. Morita, T. Nagai, H. Nishimura, T. Ozaki, J. Park, Y. Sakawa, H. Takabe, G. Williams, Z. Zhang

NEW JOURNAL OF PHYSICS 15 2013.6

We report new results from the intense laser target interaction experiment that produces relativistic electron-positron pairs. Laser to electron energy transfer, inferred using x-ray and neutron measurements, was found to be consistent with the measured positrons. To increase the number of positrons, one needs to deliver a greater number of relativistic electrons from the laser-plasma interaction to the high Z gold target. A large preplasma was found to have a negative impact for this purpose, while the laser could produce hotter electrons in such preplasma. The peak energy shift in the positron spectrum is confirmed as the post-acceleration in the sheath potential behind the target. The results were supported by a collisional one-dimensional particle-in-cell code. This experiment was performed using the high-power LFEX laser at the Institute of Laser Engineering at Osaka University using a suite of diagnostics measuring electrons, positrons, x-rays and neutrons from the laser-target interaction at the relativistic regime.

Pr or Ce-doped, fast-response and low-afterglow cross-section-enhanced scintillator with Li-6 for down-scattered neutron originated from laser fusion Reviewed

Kozue Watanabe, Yasunobu Arikawa, Kohei Yamanoi, Marilou Cadatal-Raduban, Takahiro Nagai, Masahiro Kouno, Kohei Sakai, Tomoharu Nazakato, Toshihiko Shimizu, Nobuhiko Sarukura, Mitsuo Nakai, Takayoshi Norimatsu, Hiroshi Azechi, Akira Yoshikawa, Takahiro Murata, Shigeru Fujino, Hideki Yoshida, Nobuhiko Izumi, Nakahiro Satoh, Hirofumi Kan

JOURNAL OF CRYSTAL GROWTH 362 288 - 290 2013.1

We explore the potential of Pr- or Ce-doped 20Al(PO3)(3)-80LiF (APLF80+3Pr or +3Ce) scintillator to observe the lower edge of down-scattered neutron and discriminate fusion originated neutron from strong X-ray signals. APLF80+3Pr or +3Ce scintillator exhibits considerably fast decay profiles and negligible slow-decay components. Using these newly developed APLF80+3Pr or +3Ce scintillators, we have successfully observed fusion-originated neutron signal in the midst of strong X-ray-excited fluorescence in an integrated experiment using our 10 kJ class GEKKO XII Nd-glass laser system. A sophisticated neutron detection system using APLF80+3Pr or 3Ce will be used for the first fast ignition experiment. (C) 2011 Elsevier BY. All rights reserved.

Development of time-of-flight neutron detector with fast-decay and low-afterglow scintillator for fast ignition experiment Reviewed

T. Nagai, Y. Arikawa, H. Hosoda, Y. Ioka, A. Hasegawa, K. Wada, S. Takaoku, M. Takata, K. Noritake, Y. Minami, K. Watanabe, K. Yamanoi, H. Nakamura, T. Watari, M. Cadatal-Raduban, T. Shimizu, N. Sarukura, M. Nakai, T. Norimatsu, H. Azechi

IFSA 2011 - SEVENTH INTERNATIONAL CONFERENCE ON INERTIAL FUSION SCIENCES AND APPLICATIONS 59 2013

A fast-decay and low-afterglow liquid scintillator was developed for the fast ignition experiment at the Institute of Laser Engineering (ILE). The liquid scintillator was coupled to a gated photomultiplier (PMT), and the gating performance under high-intensity gamma-rays was experimentally checked. In 2010, a detector with a high detection efficiency of 10(-4) was developed and installed in this experiment. The neutron yield in the fast heating experiment was successfully measured using this detector.

Implosion and heating experiments of fast ignition targets by Gekko-XII and LFEX lasers Reviewed

H. Shiraga, S. Fujioka, M. Nakai, T. Watari, H. Nakamura, Y. Arikawa, H. Hosoda, T. Nagai, M. Koga, H. Kikuchi, Y. Ishii, T. Sogo, K. Shigemori, H. Nishimura, Z. Zhang, M. Tanabe, S. Ohira, Y. Fujii, T. Namimoto, Y. Sakawa, O. Maegawa, T. Ozaki, K. A. Tanaka, H. Habara, T. Iwawaki, K. Shimada, M. Key, P. Norreys, J. Pasley, H. Nagatomo, T. Johzaki, A. Sunahara, M. Murakami, H. Sakagami, T. Taguchi, T. Norimatsu, H. Homma, Y. Fujimoto, A. Iwamoto, N. Miyanaga, J. Kawanaka, T. Kanabe, T. Jitsuno, Y. Nakata, K. Tsubakimoto, K. Sueda, R. Kodama, K. Kondo, N. Morio, S. Matsuo, T. Kawasaki, K. Sawai, K. Tsuji, H. Murakami, N. Sarukura, T. Shimizu, K. Mima, H. Azechi

IFSA 2011 - SEVENTH INTERNATIONAL CONFERENCE ON INERTIAL FUSION SCIENCES AND APPLICATIONS 59 2013

The FIREX-1 project, the goal of which is to demonstrate fuel heating up to 5 keV by fast ignition scheme, has been carried out since 2003 including construction and tuning of LFEX laser and integrated experiments. Implosion and heating experiment of Fast Ignition targets have been performed since 2009 with Gekko-XII and LFEX lasers. A deuterated polystyrene shell target was imploded with the 0.53-mu m Gekko-XII, and the 1.053-mu m beam of the LFEX laser was injected through a gold cone attached to the shell to generate hot electrons to heat the imploded fuel plasma. Pulse contrast ratio of the LFEX beam was significantly improved. Also a variety of plasma diagnostic instruments were developed to be compatible with harsh environment of intense hard x-rays (gamma rays) and electromagnetic pulses due to the intense LFEX beam on the target. Large background signals around the DD neutron signal in time-of-flight record of neutron detector were found to consist of neutrons via (gamma, n) reactions and scattered gamma rays. Enhanced neutron yield was confirmed by carefully eliminating such backgrounds. Neutron enhancement up to 3.5 x 10(7) was observed. Heating efficiency was estimated to be 10-20% assuming a uniform temperature rise model.

Implosion and heating experiments of fast ignition targets by Gekko-XII and LFEX lasers Reviewed

EPJ Web of Conferences 59 2013

The FIREX-1 project, the goal of which is to demonstrate fuel heating up to 5 keV by fast ignition scheme, has been carried out since 2003 including construction and tuning of LFEX laser and integrated experiments. Implosion and heating experiment of Fast Ignition targets have been performed since 2009 with Gekko-XII and LFEX lasers. A deuterated polystyrene shell target was imploded with the 0.53- μm Gekko-XII, and the 1.053- μm beam of the LFEX laser was injected through a gold cone attached to the shell to generate hot electrons to heat the imploded fuel plasma. Pulse contrast ratio of the LFEX beam was significantly improved. Also a variety of plasma diagnostic instruments were developed to be compatible with harsh environment of intense hard x-rays (γ rays) and electromagnetic pulses due to the intense LFEX beam on the target. Large background signals around the DD neutron signal in time-of-flight record of neutron detector were found to consist of neutrons via (γ,n) reactions and scattered gamma rays. Enhanced neutron yield was confirmed by carefully eliminating such backgrounds. Neutron enhancement up to 3.5 × 107 was observed. Heating efficiency was estimated to be 10-20% assuming a uniform temperature rise model. © Owned by the authors, published by EDP Sciences, 2013.

Multichannel down-scattered neutron detector for areal density measurement

Y. Arikawa, H. Hosoda, T. Nagai, K. Watanabe, K. Yamanoi, M. Cadatal-Raduban, T. Shimizu, N. Sarukura, M. Nakai, T. Norimatsu, H. Azechi, N. Izumi, T. Murata, T. Suyama, A. Yoshikawa, K. Kamada, Y. Usuki, N. Satoh, H. Kan

EPJ Web of Conferences 59 UNSP 13011 2013

A down-scattered neutron detector operating in the multichannel counting mode was developed for areal density (ρR) measurement. Equipped with a newly developed 6Li glass scintillator (APLF80), the detector was tested in a fusion experiment at the GEKKO XII facility, Osaka University, Osaka, Japan. For a low-ρR fusion shot, the detector clearly discriminated the γ-rays, primary neutrons, γ-rays produced via (n, γ) reactions from the target chamber, and neutrons scattered by the target chamber. Furthermore, the observed signal was in good agreement with predictions made by Monte Carlo simulation. © Owned by the authors, published by EDP Sciences, 2013.

Recent progress of fuel layering study for FIREX cryogenic target Reviewed

A. Iwamoto, T. Fujimura, M. Nakai, T. Norimatsu, H. Shiraga, H. Azechi, Y. Fujimoto, S. Machi, H. Sakagami

IFSA 2011 - SEVENTH INTERNATIONAL CONFERENCE ON INERTIAL FUSION SCIENCES AND APPLICATIONS 59 2013

Fast-Response and Low-Afterglow Cerium-Doped Lithium 6 Fluoro-Oxide Glass Scintillator for Laser Fusion-Originated Down-Scattered Neutron Detection Reviewed

Takahiro Murata, Yasunobu Arikawa, Kozue Watanabe, Kohei Yamanoi, Marilou Cadatal-Raduban, Takahiro Nagai, Masahiro Kouno, Kohei Sakai, Tomoharu Nakazato, Toshihiko Shimizu, Nobuhiko Sarukura, Mitsuo Nakai, Takayoshi Norimatsu, Hiroaki Nishimura, Hiroshi Azechi, Akira Yoshikawa, Shigeru Fujino, Hideki Yoshida, Nobuhiko Izumi, Nakahiro Sato, Hirofumi Kan

IEEE TRANSACTIONS ON NUCLEAR SCIENCE 59 ( 5 ) 2256 - 2259 2012.10

The photonuclear neutron and gamma-ray backgrounds in the fast ignition experiment Reviewed

Y. Arikawa, T. Nagai, H. Hosoda, Y. Abe, S. Kojima, S. Fujioka, N. Sarukura, M. Nakai, H. Shiraga, T. Ozaki, H. Azechi

Review of Scientific Instruments 83 ( 10 ) 10D909 2012.10

In the fast-ignition scheme, very hard x-rays (hereinafter referred to as γ-rays) are generated by Bremsstrahlung radiation from fast electrons. Significant backgrounds were observed around the deuterium-deuterium fusion neutron signals in the experiment in 2010. In this paper the backgrounds were studied in detail, based on Monte Carlo simulations, and they were confirmed to be γ-rays from the target, scattered γ-rays from the experimental bay walls γ'-rays), and neutrons generated by (γ, n) reactions in either the target vacuum chamber or the diagnostic instruments (γ-n neutrons). © 2012 American Institute of Physics.

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Papers - Nakai Mitsuo