Plasma and Fusion Research
Online ISSN : 1880-6821
ISSN-L : 1880-6821
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High Ion Temperature Plasmas using an ICRF Wall-Conditioning Technique in the Large Helical Device
Hiromi TAKAHASHIMasaki OSAKABESadayoshi MURAKAMIKenichi NAGAOKAHaruhisa NAKANOYasuhiko TAKEIRITetsuo SEKIKenji SAITOHiroshi KASAHARAShuji KAMIOTakashi MUTOHthe LHD Experiment Group
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2014 Volume 9 Pages 1402050

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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.

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© 2014 by The Japan Society of Plasma Science and Nuclear Fusion Research
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