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Sudden Change Events of Plasma Current during Electron-Cyclotron Current Start-Up on the QUEST Spherical Tokamak

Ryuya IKEZOE, Kosuke TAKEDA¹⁾, Kengoh KURODA, Takumi ONCHI, Takahiro NAGATA, Izumi SEKIYA, Hiroshi IDEI, Fadilla ZENNIFA, Yifan ZHANG¹⁾, Seiya SAKAI¹⁾, Rikuya MIYATA¹⁾, Takahiro YAMAGUCHI¹⁾, Makoto HASEGAWA, Yoshihiko NAGASHIMA, Takeshi IDO and Kazuaki HANADA

Research Institute for Applied Mechanics, Kyushu University, Fukuoka 816-8580, Japan

1)

Interdisciplinary Graduate School of Engineering Sciences, Kyushu University, Fukuoka 816-8580, Japan

(Received 9 January 2023 / Accepted 27 June 2023 / Published 2 August 2023)

Abstract

Non-inductive plasma current start-up experiments have been conducted using 2nd harmonic electron-cyclotron resonance heating (ECRH) on the QUEST spherical tokamak. Sudden or abrupt changes in plasma current, referred to as sudden change events (SCEs), have been frequently observed during these experiments. To investigate these events, fast magnetic activity was measured globally by installing arrays of magnetic pick-up coils inside the vacuum vessel on QUEST. Analysis revealed that all observed SCEs could be classified into three categories based on their magnetic characteristics. In one type of event, called SCE–III, the plasma current suddenly decreases by up to 50% instantaneously, occurring in a wide discharge region achieved using 2nd ECRH start-up on QUEST. These SCE–III events may potentially lead to disruptions in future discharges at higher powers.

Copyright (c) 2023 The Japan Society of Plasma Science and Nuclear Fusion Research

Keywords

spherical tokamak, non-inductive current start-up, abrupt phenomena, MHD, magnetic fluctuation, IRE

DOI: 10.1585/pfr.18.2402066

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