[Table of Contents]

Plasma and Fusion Research

Volume 9, 1402050 (2014)

Regular Articles

High Ion Temperature Plasmas using an ICRF Wall-Conditioning Technique in the Large Helical Device
Hiromi TAKAHASHI, Masaki OSAKABE, Sadayoshi MURAKAMI1), Kenichi NAGAOKA, Haruhisa NAKANO, Yasuhiko TAKEIRI, Tetsuo SEKI, Kenji SAITO, Hiroshi KASAHARA, Shuji KAMIO, Takashi MUTOH and the LHD Experiment Group
National Institute for Fusion Science, 322-6 Oroshi-cho, Toki 509-5292, Japan
1)
Department of Nuclear Engineering, Kyoto University, Kyoto 606-8501, Japan
(Received 16 December 2013 / Accepted 8 March 2014 / Published 7 May 2014)

Abstract

A new effective wall-conditioning technique was proposed for realizing high ion temperature (Ti) plasmas in the Large Helical Device using the ion cyclotron range of frequency (ICRF) wave under the established magnetic confinement field. A series of ICRF heating discharges using He as the working gas was conducted ahead of the high-Ti plasma discharges. After sufficient repetitive wall-conditioning discharges, we observed a decrease in the line-averaged electron density, the formation of a peaked electron density profile, a reduction in the Hα emission, and an increase in the central Ti. The results suggest that the stored hydrogen inside the vacuum vessel structures, such as the first wall, the diverter, and other components, sputtered out owing to the He plasmas of the ICRF wall-conditioning discharges and the hydrogen recycling was decreased. Consequently, the ion heating power of NBI increased in the plasma core region, leading to higher central Ti.

Keywords

wall conditioning, recycling, plasma wall interaction, ICRF, high temperature, Large Helical Device

DOI: 10.1585/pfr.9.1402050

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This paper may be cited as follows:

Hiromi TAKAHASHI, Masaki OSAKABE, Sadayoshi MURAKAMI, Kenichi NAGAOKA, Haruhisa NAKANO, Yasuhiko TAKEIRI, Tetsuo SEKI, Kenji SAITO, Hiroshi KASAHARA, Shuji KAMIO, Takashi MUTOH and the LHD Experiment Group, Plasma Fusion Res. 9, 1402050 (2014).