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Al
GaO
scintillators by gamma-ray-induced positron annihilation lifetime spectroscopyFujimori, Kosuke*; Kitaura, Mamoru*; Taira, Yoshitaka*; Fujimoto, Masaki*; Zen, H.*; Watanabe, Shinta*; Kamada, Kei*; Okano, Yasuaki*; Kato, Masahiro*; Hosaka, Masahito*; et al.
Applied Physics Express, 13(8), p.085505_1 - 085505_4, 2020/08
Times Cited Count：5 Percentile：33.01(Physics, Applied)To clarify the existence of cation vacancies in Ce-doped GdAlGaO (Ce:GAGG) scintillators, we performed gamma-ray-induced positron annihilation lifetime spectroscopy (GiPALS). GiPAL spectra of GAGG and Ce:GAGG comprised two exponential decay components, which were assigned to positron annihilation at bulk and defect states. By an analogy with Ce:YAl
O, the defect-related component was attributed to Al/Ga-O divacancy complexes. This component was weaker for Ce, Mg:GAGG, which correlated with the suppression of shallow electron traps responsible for phosphorescence. Oxygen vacancies were charge compensators for Al/Ga vacancies. The lifetime of the defect-related component was significantly changed by Mg co-doping. This was understood by considering aggregates of Mg
ions at Al/Ga sites with oxygen vacancies, which resulted in the formation of vacancy clusters.
Sasaki, Akira; Kato, Susumu*; Takahashi, Eiichi*; Kishimoto, Yasuaki*; Fujii, Takashi*; Kanazawa, Seiji*
Japanese Journal of Applied Physics, 55(2), p.026101_1 - 026101_10, 2016/02
Times Cited Count：2 Percentile：9.68(Physics, Applied)A percolation model of discharge, which can reproduce stochastic behaviors of initial partial discharge to the growth of a stepped leader, is presented. The model uses macroscopic cells, from which a network of electric circuits is defined, and the spatial and temporal evolutions of the electric field and current in the discharge medium are calculated. For each cell, one of two states, either insulator or conductor, which corresponds to neutral gas or ionized plasmas, respectively, is decided. The decision is made on the basis of probability for each calculation cell at each time step, taking the effects of local electric field and current, which enhance ionization and sustain the discharge channel, respectively, into account. The stochastic behavior of discharge is discussed, in conjunction with the characteristic feature of ionization, that is, the ionization occurs not only ahead of the streamer tip where the electric field is enhanced but randomly in the discharge medium.
Takahashi, Eiichi*; Kato, Susumu*; Furutani, Hirohide*; Sasaki, Akira; Kishimoto, Yasuaki*; Takada, Kenji*; Matsumura, Satoshi*; Sasaki, Hiroyasu*
Journal of Physics D; Applied Physics, 44(30), p.302001_1 - 302001_4, 2011/08
Times Cited Count：7 Percentile：31.23(Physics, Applied)A recently developed ultrafast camera that can acquire 
frames per second was used to investigate positive streamer discharge. It enabled single-shot evaluation of streamer evolution without the need to consider shot-to-shot reproducibility. This camera was used to investigate streamers in argon. Growing branches, the transition when a streamer forms a return stroke, and related phenomena were clearly observed.
Takahashi, Eiichi*; Kato, Susumu*; Sasaki, Akira; Kishimoto, Yasuaki*; Furutani, Hirohide*
Journal of Physics D; Applied Physics, 44(7), p.075204_1 - 075204_6, 2011/02
Times Cited Count：20 Percentile：62.85(Physics, Applied)Positive streamer branching in atmospheric argon gas was controlled by a KrF laser irradiation. This laser irradiation changes the amount of background ionization before the streamer discharge. Initial electron density formed by the KrF laser was evaluated by measuring ionization current. Characteristic "feather like" branching structure was observed and was suppressed only for the irradiated region. The threshold of ionization density which can influence to the branching was evaluated to be 5
10
/cm
. This suppression behavior was explained by the relation between a size of avalanche head and mean initial electron distance. These experimental results support the origin of the feather like structure comes from the branching model of Loeb-Meek that is probabilistic merging of individual avalanches.
Sasaki, Akira; Kishimoto, Yasuaki*; Takahashi, Eiichi*; Kato, Susumu*; Fujii, Takashi*; Kanazawa, Seiji*
Physical Review Letters, 105(7), p.075004_1 - 075004_4, 2010/08
Times Cited Count：10 Percentile：55.33(Physics, Multidisciplinary)A three-dimensional simulation of laser guided-discharges based on the percolation is presented. The model includes both local growth of a streamer due to the enhanced electric field at the tip and propagation of a leader by remote ionization such that caused by runaway electrons. The stochastic behavior of the discharge through preformed plasma channel is reproduced by the calculation, which shows complex path with detouring and bifurcation. The probability of guiding is investigated with respect to the ionized, conductive fraction along the channel.
Sasaki, Akira; Takahashi, Eiichi*; Kato, Susumu*; Kishimoto, Yasuaki*
Denki Gakkai Parusu Pawa, Hoden Godo Kenkyukai Shiryo (PPT-09-95, ED-09-139), p.9 - 13, 2009/10
A new simulation model of the initiation of high pressure discharge is presented. The model reproduces branching and detouring properties of the discharge path. The model is based on combined random percolation and electric circuit models. We show that the idea of phase transition allows one to renormalize the effect of elementary atomic processes and to perform calculation of the discharge path with a realistic scale (mm to km). As a simple application of the model, discharge through a pre-ionized channel created by a laser irradiation, is investigated, which shows stochastic behaviors of the discharge guiding.
Kato, Susumu*; Takahashi, Eiichi*; Sasaki, Akira; Kishimoto, Yasuaki*
Purazuma, Kaku Yugo Gakkai-Shi, 84(8), p.477 - 483, 2008/08
no abstracts in English
Nishiwaki, Yoichi*; Kato, Tetsuya*; Ohara, Yasuaki*; Osawa, Akira*; Todoroki, Norikazu*; Igawa, Naoki; Ishii, Yoshinobu; Iio, Katsunori*
Journal of the Physical Society of Japan, 75(3), p.034707_1 - 034707_8, 2006/03
Times Cited Count：12 Percentile：58.26(Physics, Multidisciplinary)no abstracts in English
Sasaki, Akira; Takahashi, Eiichi*; Kato, Susumu*; Kishimoto, Yasuaki*
no journal, ,
no abstracts in English
Kato, Atsushi; Negishi, Kazuo; Sato, Kenichiro*; Akiyama, Yo*; Hara, Hiroyuki*; Iwasaki, Mikinori*; Abe, Ganji*; Tokiyoshi, Takumi*; Okafuji, Takashi*; Umeki, Katsuhiko*; et al.
no journal, ,
Report research and development activities related to steel plate reinforced concrete containment vessel for the JSFR conducted as a part of METI commissioned research.
Sasaki, Akira; Takahashi, Eiichi*; Kato, Susumu*; Kishimoto, Yasuaki*; Kanazawa, Seiji*; Fujii, Takashi*
no journal, ,
no abstracts in English
Kato, Atsushi; Negishi, Kazuo; Akiyama, Yo*; Iwasaki, Mikinori*; Okafuji, Takashi*; Abe, Ganji*; Somaki, Takahiro*; Umeki, Katsuhiko*; Fukushima, Yasuaki*; Sawamoto, Yoshikazu*
no journal, ,
Steel plate reinforced concrete structure are adopted as the JSFR containment vessel to shorten a construction period. This reports project summary of SCCV Research and Development.
Sasaki, Akira; Takahashi, Eiichi*; Kato, Susumu*; Kishimoto, Yasuaki*; Fujii, Takashi*; Kanazawa, Seiji*; Torii, Tatsuo
no journal, ,
no abstracts in English
Sasaki, Akira; Torii, Tatsuo; Takahashi, Eiichi*; Kato, Susumu*; Kishimoto, Yasuaki*; Kanazawa, Seiji*; Fujii, Takashi*
no journal, ,
no abstracts in English
Sasaki, Akira; Torii, Tatsuo; Kato, Susumu*; Takahashi, Eiichi*; Fujii, Takashi*; Kanazawa, Seiji*; Kishimoto, Yasuaki*
no journal, ,
no abstracts in English
Sasaki, Akira; Takahashi, Eiichi*; Kato, Susumu*; Kishimoto, Yasuaki*; Fujii, Takashi*; Kanazawa, Seiji*
no journal, ,
The discharge simulation based on the percolation model is extended to include the dynamics of formation and extincition of the ionized region in the gas, and the temporal evolution of discharge current is calculated taking spatial capacitance and inductance into account. Calculations show prebreakdown activity appears in front of the protrution on the electrode after some delay from a high voltage is applied across the gap, which is followed by the development of the stepped leader and the establishment of a discharge path between the electrondes.
Sasaki, Akira; Kato, Susumu*; Takahashi, Eiichi*; Fujii, Takashi*; Kanazawa, Seiji*; Kishimoto, Yasuaki*
no journal, ,
no abstracts in English
Sasaki, Akira; Kato, Susumu*; Takahashi, Eiichi*; Fujii, Takashi*; Kanazawa, Seiji*; Kishimoto, Yasuaki*
no journal, ,
no abstracts in English
Sasaki, Akira; Torii, Tatsuo; Takahashi, Eiichi*; Kato, Susumu*; Fujii, Takashi*; Kanazawa, Seiji*; Kishimoto, Yasuaki*
no journal, ,
no abstracts in English
Sasaki, Akira; Torii, Tatsuo; Kato, Susumu*; Takahashi, Eiichi*; Kishimoto, Yasuaki*; Fujii, Takashi*; Kanazawa, Seiji*; Odagaki, Takashi*
no journal, ,
no abstracts in English
