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Umeda, Maki; Chudo, Hiroyuki; Imai, Masaki; Sato, Nana; Saito, Eiji
Review of Scientific Instruments, 94(6), p.063906_1 - 063906_8, 2023/06
Times Cited Count:0 Percentile:0(Instruments & Instrumentation)Chudo, Hiroyuki; Imai, Masaki; Matsuo, Mamoru; Maekawa, Sadamichi; Saito, Eiji
Journal of the Physical Society of Japan, 90(8), p.081003_1 - 081003_11, 2021/08
Times Cited Count:3 Percentile:41.09(Physics, Multidisciplinary)Chudo, Hiroyuki; Imai, Masaki
Kotai Butsuri, 55(9), p.435 - 443, 2020/09
no abstracts in English
Imai, Masaki; Chudo, Hiroyuki; Matsuo, Mamoru; Maekawa, Sadamichi; Saito, Eiji
Physical Review B, 102(1), p.014407_1 - 014407_5, 2020/07
Times Cited Count:6 Percentile:38.95(Materials Science, Multidisciplinary)Kaneko, Koji; Cheung, Y. W.*; Hu, Y.*; Imai, Masaki*; Tanioku, Yasuaki*; Kanagawa, Hibiki*; Murakawa, Joichi*; Moriyama, Kodai*; Zhang, W.*; Lai, K. T.*; et al.
JPS Conference Proceedings (Internet), 30, p.011032_1 - 011032_6, 2020/03
Imai, Masaki; Chudo, Hiroyuki; Ono, Masao; Harii, Kazuya; Matsuo, Mamoru; Onuma, Yuichi*; Maekawa, Sadamichi; Saito, Eiji
Applied Physics Letters, 114(16), p.162402_1 - 162402_4, 2019/04
Times Cited Count:20 Percentile:73.01(Physics, Applied)Cheung, Y. W.*; Hu, Y. J.*; Imai, Masaki*; Tanioku, Yasuaki*; Kanagawa, Hibiki*; Murakawa, Joichi*; Moriyama, Kodai*; Zhang, W.*; Lai, K. T.*; Yoshimura, Kazuyoshi*; et al.
Physical Review B, 98(16), p.161103_1 - 161103_5, 2018/10
Times Cited Count:19 Percentile:67.24(Materials Science, Multidisciplinary)Imai, Masaki; Ogata, Yudai*; Chudo, Hiroyuki; Ono, Masao; Harii, Kazuya; Matsuo, Mamoru*; Onuma, Yuichi*; Maekawa, Sadamichi; Saito, Eiji
Applied Physics Letters, 113(5), p.052402_1 - 052402_3, 2018/07
Times Cited Count:18 Percentile:65.6(Physics, Applied)Cheung, Y. W.*; Hu, Y. J.*; Goh, S. K.*; Kaneko, Koji; Tsutsui, Satoshi; Logg, P. W.*; Grosche, F. M.*; Kanagawa, Hibiki*; Tanioku, Yasuaki*; Imai, Masaki*; et al.
Journal of Physics; Conference Series, 807(3), p.032002_1 - 032002_4, 2017/04
Times Cited Count:5 Percentile:83.59(Physics, Condensed Matter)Imai, Masaki; Michioka, Chishiro*; Ueda, Hiroaki*; Yoshimura, Kazuyoshi*
Physical Review B, 95(5), p.054417_1 - 054414_7, 2017/02
Times Cited Count:2 Percentile:11.52(Materials Science, Multidisciplinary)We took P NMR measurements of mainly paramagnetic phase to reveal the itinerant-electron metamagnetic transition, and of its magnetically ordered phase, and characterized their spin fluctuations by estimating the spin fluctuation parameter corresponding to the width of the spin fluctuation in the spectrum in frequency space. As increases from 0 to 0.5, the in-plane component of decreases proportionally with the metamagnetic transition field. In the antiferromagnetic cT phase, is constant and spin fluctuations show an isotropic character in contrast to their behavior in the paramagnetic ucT phase. These results indicate that the in-plane spin fluctuations due to the quasi-two-dimensional crystal structure play a significant role in the metamagnetic transition of this system.
Cheung, Y. W.*; Zhang, J. Z.*; Zhu, J. Y.*; Yu, W. C.*; Hu, Y. J.*; Wang, D. G.*; Otomo, Yuka*; Iwasa, Kazuaki*; Kaneko, Koji; Imai, Masaki*; et al.
Physical Review B, 93(24), p.241112_1 - 241112_5, 2016/06
Times Cited Count:14 Percentile:54.92(Materials Science, Multidisciplinary)Kashiwagi, Mieko; Hanada, Masaya; Yamana, Takashi*; Inoue, Takashi; Imai, Tsuyoshi*; Taniguchi, Masaki; Watanabe, Kazuhiro
Fusion Engineering and Design, 81(23-24), p.2863 - 2869, 2006/11
Times Cited Count:4 Percentile:30.68(Nuclear Science & Technology)Plasma neutralizer is one of key components to achieve the required system efficiency ( 50 %) for a negative-ion based neutral beam (N-NB) system in a fusion power plant. In the plasma neutralizer, highly ionized plasma is required at lower pressure, e.g., ionization degrees of 30 % at 0.08 Pa for 1 MeV negative ions. In such low pressure, mean free path of fast electron that contributes to ionizations becomes longer than the neutralizer's dimensions. Therefore, suppression of fast electron leakage from large openings that are beam entrance and exit is a crucial issue to realize plasma neutralizers. To suppress the fast electron leakage from the openings, authors propose a shield field, which is a weak transverse magnetic field of only 30 Gauss applied locally around the opening. The shield field are numerically examined and designed by using a three dimensional particle orbit code. In the experimental studies, this weak shield field is applied at the openings (diam. = 20 cm) of an arc discharge driven plasma neutralizer (length = 200 cm, diam. = 60 cm). The plasma parameters inside and outside of the opening were measured by a Langmuir probe. The electron energy distribution function (EEDF) showed that considerable fast electrons, which were leaked from the opening, were suppressed successfully by the weak shield field of 30 Gauss. Thus the leaking fast electrons were repelled into the neutralizer to deposit their energy for the plasma production. At a result, the plasma production efficiency (plasma density / arc power) was improved by a factor of 1.5 at 0.08 Pa.
Hanada, Masaya; Seki, Takayoshi*; Takado, Naoyuki*; Inoue, Takashi; Morishita, Takatoshi; Mizuno, Takatoshi*; Hatayama, Akiyoshi*; Imai, Tsuyoshi*; Kashiwagi, Mieko; Sakamoto, Keishi; et al.
Fusion Engineering and Design, 74(1-4), p.311 - 317, 2005/11
Times Cited Count:7 Percentile:44.9(Nuclear Science & Technology)no abstracts in English
Inoue, Takashi; Taniguchi, Masaki; Morishita, Takatoshi; Dairaku, Masayuki; Hanada, Masaya; Imai, Tsuyoshi*; Kashiwagi, Mieko; Sakamoto, Keishi; Seki, Takayoshi*; Watanabe, Kazuhiro
Nuclear Fusion, 45(8), p.790 - 795, 2005/08
The R&D of a 1 MeV accelerator and a large negative ion source have been carried out at JAERI. The paper presents following progress as a step toward ITER NB system. (1) Accelerator R&D: According to success in improvement of voltage holding capability, the acceleration test of H ions up to 1 MeV class energy is in progress. H ion beams of 1 MeV, 100 mA class have been generated with a substantial beam current density (100 A/m), and the current density is still increasing by the ion source tuning. (2) Large ion source R&D: One of major causes that limited the NB injection performance was spatial unifomity of negative ion production in existing negative-ion based NB systems. The present study revealed that the negative ions produced in the extraction region of the source were locally destructed by fast electrons leaking through magnetic filter. Some countermeasures and their test results are also described.
Inoue, Takashi; Taniguchi, Masaki; Morishita, Takatoshi; Dairaku, Masayuki; Hanada, Masaya; Imai, Tsuyoshi*; Kashiwagi, Mieko; Sakamoto, Keishi; Seki, Takayoshi*; Watanabe, Kazuhiro
Nuclear Fusion, 45(8), p.790 - 795, 2005/08
Times Cited Count:23 Percentile:59.63(Physics, Fluids & Plasmas)The R&D of a 1 MeV accelerator and a large negative ion source has been carried out at JAERI for the ITER NB system. The R&D is in progress at present toward: (1) 1 MeV acceleration of H ion beams at the ITER relevant current density of 200 A/m, and (2) improvement of uniform negative ion production over wide extraction area in large negative ion sources. Recently, H ion beams of 1 MeV, 140 mA level have been generated with a substantial beam current density (100 A/m). In the uniformity study, it has been clarified that electron temperature in the ion extraction region is locally high ( 1 eV), which resulted in destruction of negative ions at a high reaction rate. Interception of fast electrons leaking through a transverse magnetic field called "magnetic filter" has been found effective to lower the local electron temperature, followed by an improvement of negative ion beam profile.
Inoue, Takashi; Taniguchi, Masaki; Dairaku, Masayuki; Hanada, Masaya; Kashiwagi, Mieko; Morishita, Takatoshi; Watanabe, Kazuhiro; Imai, Tsuyoshi
Review of Scientific Instruments, 75(5), p.1819 - 1821, 2004/05
Times Cited Count:11 Percentile:51.25(Instruments & Instrumentation)The paper reports progress of proof-of-principle test of negative ion accelerator for ITER. The accelerator structure is immersed in vacuum, surrounded by a FRP insulator column as the vacuum boundary. So far, the beam energy has been limited due to poor voltage holding capability of the FRP insulator column. By lowering the electric field strength at the triple junction (interface of FRP insulator, metal flange and vacuum) with large stress ring installed inside the insulator column, high voltage of 1 MV was stably sustained for more than 2 hours. In the following beam test, acceleration of 900 keV, 100 mA H ion beam was succeeded. Although the current was lower (70 mA) at 1 MeV, the beam of this level has been stably accelerated for 6 days, 130 shots in total (each pulse length: 1 s).
Inoue, Takashi; Hanada, Masaya; Iga, Takashi*; Imai, Tsuyoshi; Kashiwagi, Mieko; Kawai, Mikito; Morishita, Takatoshi; Taniguchi, Masaki; Umeda, Naotaka; Watanabe, Kazuhiro; et al.
Fusion Engineering and Design, 66-68, p.597 - 602, 2003/09
Times Cited Count:21 Percentile:78.49(Nuclear Science & Technology)The neutral beam (NB) injection has been one of the most promising methods for plasma heating and current drive in tokamak fusion devices. JAERI has developed high energy electrostatic accelerators for the NB systems in JT-60U and ITER. Recent progress on this R&D are as follows: 1) In the JT-60U NB system, some of the beams has been deflected due to distorted electric field in the accelerator, resulting in an excess heat load on the NB port. By correcting the electric field, a continuous injection of H beam was succeeded for 10 s with the NB power of 2.6 MW at 355 keV. 2) To increase the beam energy, a metal structure called stress ring was designed. The ring reduces electric field concentration at the triple junction point (interface between metal and dielectric insulator inside vacuum). Initial test of the accelerators with the stress rings has shown higher voltage hold off performance in both accelerators for JT-60U and ITER R&D than that without rings.
Taniguchi, Masaki; Hanada, Masaya; Iga, Takashi*; Inoue, Takashi; Kashiwagi, Mieko; Morishita, Takatoshi; Okumura, Yoshikazu; Shimizu, Takashi; Takayanagi, Tomohiro; Watanabe, Kazuhiro; et al.
Nuclear Fusion, 43(8), p.665 - 669, 2003/08
Times Cited Count:16 Percentile:46.47(Physics, Fluids & Plasmas)no abstracts in English
Watanabe, Kazuhiro; Iga, Takashi*; Morishita, Takatoshi; Kashiwagi, Mieko; Inoue, Takashi; Hanada, Masaya; Taniguchi, Masaki; Imai, Tsuyoshi
Proceedings of 28th Linear Accelerator Meeting in Japan, p.186 - 188, 2003/08
no abstracts in English
Morishita, Takatoshi; Inoue, Takashi; Iga, Takashi*; Watanabe, Kazuhiro; Kashiwagi, Mieko; Shimizu, Takashi; Taniguchi, Masaki; Hanada, Masaya; Imai, Tsuyoshi
JAERI-Tech 2003-007, 16 Pages, 2003/03
Recently the ion source for IFMIF (International Fusion Material Irradiation facility) achieved positive ion beams of 120 mA with the proton ratio of 90% by applying magnetic filter even in a small ion source. The mechanism of a high proton ration plasma production in such a small ion source has not been studied. Molecular ions are destroyed and the proton is produced from the dissociation of molecular ions in the filter region. Thus the proton yield is enhanced even in the small volume discharge. Using the same numerical method, the plasma production was calculated for the large ion source. The high proton ratio can be easily obtained, where the contribution of proton production by the ionization of H becomes high. From the negative ion production point of view, the negative ion beam current was numerically evaluated. The high atom flux to the plasma grid generates the large amount of negative ions rather than that by the positive ions in Cs-seeded large ion sources.