Effect of magnetic structure on RF-induced breakdown in QUEST

R. Yoneda, K. Hanada, K. Nakamura, H. Idei, N. Yoshida, M. Hasegawa, T. Onchi, K. Kuroda, S. Kawasaki, A. Higashijima, T. Nagata, A. Isayama, O. Mitarai, A. Fukuyama, Y. Takase

Research output: Contribution to journalArticle

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Abstract

In tokamak operations, breakdown of plasma is the first step of the plasma build-up. In this paper, we present a combinative investigation of radio frequency (RF)-induced breakdown experiments in QUEST (Q-shu University Experiment with Steady-State Spherical Tokamak) and a one-point model of hydrogen ionization. Experimental results with two different frequencies of 2.45 GHz and 8.2 GHz showed that the clear threshold on connection length, L, existed for breakdown with a negative n-index configuration n=-(R/Bv)·(∂Bv/∂R), where R is the major radius and Bv the is vertical magnetic field. In contrast, breakdown was always obtained with positive n-index when changing L. It indicates that a lifetime of an incubated electron plays a significant role in the plasma breakdown. According to one-point model calculation, the experimental threshold of L is well predicted by the lifetime of the incubated electron estimated by employing the loss term along with L. The model calculation also describes the requirement of the minimum electron temperature Te for RF-induced breakdown to realize an avalanche of electrons in the tokamak magnetic structure.

Original languageEnglish
Article number062513
JournalPhysics of Plasmas
Volume24
Issue number6
DOIs
Publication statusPublished - Jun 1 2017

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radio frequencies
breakdown
life (durability)
electrons
thresholds
avalanches
electron energy
ionization
requirements
radii
hydrogen
configurations
magnetic fields

All Science Journal Classification (ASJC) codes

  • Condensed Matter Physics

Cite this

Effect of magnetic structure on RF-induced breakdown in QUEST. / Yoneda, R.; Hanada, K.; Nakamura, K.; Idei, H.; Yoshida, N.; Hasegawa, M.; Onchi, T.; Kuroda, K.; Kawasaki, S.; Higashijima, A.; Nagata, T.; Isayama, A.; Mitarai, O.; Fukuyama, A.; Takase, Y.

In: Physics of Plasmas, Vol. 24, No. 6, 062513, 01.06.2017.

Research output: Contribution to journalArticle

Yoneda, R, Hanada, K, Nakamura, K, Idei, H, Yoshida, N, Hasegawa, M, Onchi, T, Kuroda, K, Kawasaki, S, Higashijima, A, Nagata, T, Isayama, A, Mitarai, O, Fukuyama, A & Takase, Y 2017, 'Effect of magnetic structure on RF-induced breakdown in QUEST', Physics of Plasmas, vol. 24, no. 6, 062513. https://doi.org/10.1063/1.4985142
Yoneda, R. ; Hanada, K. ; Nakamura, K. ; Idei, H. ; Yoshida, N. ; Hasegawa, M. ; Onchi, T. ; Kuroda, K. ; Kawasaki, S. ; Higashijima, A. ; Nagata, T. ; Isayama, A. ; Mitarai, O. ; Fukuyama, A. ; Takase, Y. / Effect of magnetic structure on RF-induced breakdown in QUEST. In: Physics of Plasmas. 2017 ; Vol. 24, No. 6.
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