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Suppression of "Edge MHD Instability of LHD" by External RMP

Shu ITO¹⁾, Kiyomasa WATANABE^1,2), Yuki TAKEMURA^2,3), Satoru SAKAKIBARA^2,3) and Sadao MASAMUNE⁴⁾

1)

Nagoya University, Graduate School of Engineering, Chikusa, Nagoya 464-8603, Japan

2)

National Institute for Fusion Science, National Institutes of Natural Sciences, Toki, Gifu 509-5292, Japan

3)

SOKENDAI (The Graduate University for Advanced Studies), Toki, Gifu 509-5292, Japan

4)

Chubu University, Graduate School of Engineering, Kasugai, Aichi 487-8501, Japan

(Received 18 October 2023 / Accepted 20 November 2023 / Published 8 February 2024)

Abstract

We experimentally investigate the effect of external resonant magnetic perturbation (RMP) on "Edge MHD instability", which is observed in a discharge with relatively low magnetic Reynolds number and middle beta in the Large Helical Device (LHD) and leads to minor collapse (rapid degradation of volum-averaged beta value by 10%). When the external RMP is small, the instability is continuously observed in a discharge, and the fluctuation amplitude decreases a little with the increment of the RMP. When the RMP is large enough, the appearance of the instability becomes intermittent, and the fluctuation amplitude rapidly decreases with the increment of the RMP. Moreover, the confinement performance degraded by the instability also recovers when the intermittent instability appears.

Copyright (c) 2024 The Japan Society of Plasma Science and Nuclear Fusion Research

Keywords

LHD, MHD instability, RMP, magnetic confinement, helical plasma

DOI: 10.1585/pfr.19.1402001

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