CVClient

永田 正義

永田 正義  (Masayoshi Nagata)

基本情報

所属
兵庫県立大学 大学院工学研究科 (特任教授、名誉教授)
学位
工学博士(大阪大学)

連絡先
nagataeng.u-hyogo.ac.jp
J-GLOBAL ID
202001003652450887
researchmap会員ID
R000013290

論文

 93
  • K. Kuroda, R. Raman, T. Onchi, M. Hasegawa, K. Hanada, M. Ono, B.A. Nelson, J. Rogers, R. Ikezoe, H. Idei, T. Ido, M. Nagata, O. Mitarai, N. Nishino, Y. Otsuka, Y. Zhang, K. Kono, S. Kawasaki, T. Nagata, A. Higashijima, S. Shimabukuro, I. Niiya, I. Sekiya, K. Nakamura, Y. Takase, A. Ejiri, S. Murakami
    Nuclear Fusion 64(1) 014002-014002 2023年12月1日  
    Abstract Results from the successful solenoid-free plasma startup using the method of transient coaxial helicity injection (transient CHI) in the QUEST spherical tokamak (ST) are reported. Unlike previous applications of CHI on HIT-II and on NSTX which required two toroidal insulating breaks to the vacuum vessel, QUEST uses a first of its kind, floating single biased electrode configuration, which does not use such a vacuum break. Instead, the CHI electrode is simply insulated from the outer lower divertor plate support structure. This configuration is much more suitable for implementation in a fusion reactor than the previous configurations. Transient CHI generated toroidal currents of 135 kA were obtained. The toroidal current during the formation of a closed flux configuration was over 50 kA. These results bode well for the application of transient CHI in a new generation of compact high-field STs and tokamaks in which the space for the central solenoid is very restricted.
  • K. Kuroda, R. Raman, M. Hasegawa, T. Onchi, K. Hanada, M. Ono, B. A. Nelson, J. Rogers, R. Ikezoe, H. Idei, T. Ido, O. Mitarai, M. Nagata, S. Kawasaki, T. Nagata, A. Higashijima, S. Shimabukuro, I. Niiya, I. Sekiya, S. Kojima, K. Nakamura, Y. Takase, S. Murakami
    Journal of Fusion Energy 41 25 2022年10月  査読有り
  • Y. Takase, A. Ejiri, T. Fujita, K. Hanada, H. Idei, M. Nagata, T. Onchi, Y. Ono, H. Tanaka, N. Tsujii, M. Uchida, K. Yasuda, H. Kasahara, S. Murakami, Y. Takeiri, Y. Todo, S. Tsuji-Iio, Y. Kamada
    Nuclear Fusion 62(4) 042011-042026 2022年4月  査読有り
    Spherical tokamak (ST) research in Japan has produced many innovative results: (i) plasma start-up to I p > 70 kA was achieved by electron cyclotron wave (ECW) with N ∥ = 0.75, while electron heating to T e > 500 eV was achieved with N ∥ = 0.26 on QUEST. (ii) The radiofrequency (RF)-induced transport model was combined with the x-ray emission model, and extended magnetohydrodynamics equilibrium with kinetic electrons was developed to interpret fast-electron-dominated lower hybrid wave sustained plasmas on TST-2. (iii) Density as high as 30 times the cutoff density was achieved by electron Berstein wave current drive combined with electron beam injection on LATE. (iv) Multiple plasmoids formed by tearing instability in the elongated current sheet were observed, and flux closure and ion heating by plasmoid-mediated fast magnetic reconnection were observed on HIST. (v) Optimization of ECW-assisted inductive start-up with a vertical field with positive decay index was performed on TST-2. (vi) Stabilization of the vertical displacement event by a set of upper and lower helical field coils was demonstrated on TOKASTAR-2. (vii) A 6 h discharge was achieved by cool-down of the center stack cover on QUEST, where the plasma duration limit was consistent with the wall saturation time estimated by modeling. (viii) Extension of ion heating by plasma merging was achieved on TS-3U, TS-4U, UTST, MAST, and ST40.
  • M. Nagata, Y. Ibaragi, H. Miyamoto, A. Fujita, Y. Kikuchi, N. Fukumoto
    46th EPS Conference on Plasma Physics, EPS 2019 2019年  
    Multiple plasmoid reconnection required for the flux closure in the transient-coaxial helicity injection (T-CHI) start-up process has been demonstrated in the Helicity Injected Spherical Torus (HIST) device. Two or three plasmoids are generated after the tearing instability of an elongated Sweet-Parker current sheet during the T-CHI. Here, we report that in the T-CHI start-up plasmas (H, D and He) with the strong toroidal (guide) field (ITF=140 kA), (i) the frequency of regular oscillations of reconnecting magnetic field decreases as the mass number increases, i.e., 250 kHz (H), 150 kHz (D) and 60 kHz (He). (ii) the oscillation propagates radially with 30 km/s (H), 20 km/s (D) and 12-18 km/s (He) from R= 0.25 m at the X-point toward the outboard side. It has been found that the propagation speed agrees with the Alfven speed. Consequently, the plasmoid reconnection could be related to the excitation of Alfven wave, leading to the ion heating in the T-CHI start-up plasmas.
  • T. Kanki, M. Nagata
    International Journal of Applied Electromagnetics and Mechanics 59(2) 439-446 2019年  査読有り
    Two-fluid (ions and electrons) flowing equilibrium configurations of spherical torus plasma are numerically determined by using the multi-grid method. The axisymmetric equilibrium equations consist of a pair of second-order partial differential equations for the magnetic (electron) and ion stream functions, and Bernoulli equations for the density. It is found from the numerical results that the multi-grid method with the damped Jacobi method in the smoothing step is effective for solving these equations with numerical stability, high accuracy, and high speed.

MISC

 36

書籍等出版物

 3

講演・口頭発表等

 59

担当経験のある科目(授業)

 4

共同研究・競争的資金等の研究課題

 15