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Spectroscopic Study of Molybdenum Impurity Generation in LHW Sustained Plasmas on TST-2 Spherical Tokamak

Yiming TIAN, Akira EJIRI, Naoto TSUJII, Yuting LIN, Kouji SHINOHARA, Seowon JANG, Yi PENG, Kotaro IWASAKI and Fumiya ADACHI

Graduate School of Frontier Sciences, The University of Tokyo, Kashiwa 277-8561, Japan

(Received 30 November 2023 / Accepted 4 January 2024 / Published 15 February 2024)

Abstract

Impurity generation mechanisms including RF sheath sputtering and heating from fast electrons were explored in LHW sustained plasmas on TST-2 spherical tokamak. Molybdenum impurity was measured with a high-resolution spectrometer and the heating effect on a molybdenum target plate was estimated with a fast camera system. The LHW power modulation experiment indicates that the RF sheath sputtering dominated impurity generation from the antenna limiters (molybdenum) under the current plasma parameters. In addition, the target plate insertion experiment shows that molybdenum atoms were released from the target when heated by fast electrons accelerated by LHW. Although the heating effect was negligible for the antenna limiters, it could become significant under higher plasma parameters or during longer pulses.

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

Keywords

lower hybrid current drive, impurity, RF sheath, fast electron

DOI: 10.1585/pfr.19.1402010

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