Plasma and Fusion Research

Volume 8, 2401035 (2013)

Regular Articles

Extraction of Negative Hydrogen Ions from Radio Frequency Driven Plasma Sources for Fusion Plasma Heating

Motoi WADA, Tomoya ICHIKAWA, Toshiro KASUYA, Takahiro KENMOTSU¹⁾, Masaki NISHIURA²⁾, Hiroshi TAKEMURA and Hitoshi YAMAOKA³⁾

: Graduate School of Science and Engineering, Doshisha University, Kyotanabe, Kyoto 610-0321, Japan
1): Faculty of Life and Medical Sciences, Doshisha University, Kyotanabe, Kyoto 610-0321, Japan
2): National Institute for Fusion Science, Oroshi-cho, Toki 509-5292, Japan
3): Harima Institute, Riken, Kouto, Sayo, Hyogo 679-5148, Japan

(Received 7 December 2012 / Accepted 18 February 2013 / Published 22 May 2013)

Abstract

Microwave power at 14 GHz frequency coupled to a magnetic field aligned parallel to the beam extraction axis successfully excited a plasma in a compact negative hydrogen (H⁻) ion source. A volume of low electron temperature plasma was formed based on the idea of “tent filter” magnetic field geometry by placing the extraction aperture at a recess made inside of a magnetic material. The amount of H⁻ current increased by enlarging a volume of low electron temperature plasma, which seemed consistent with the two step model of H⁻ production via vibrational excitation of hydrogen molecules. The depth of the recess was made shallower expecting the H⁻ current with the magnitude halfway between the one without the volume of low electron temperature plasma and the one with the volume. The result has indicated the expected correlation between the size of the volume and the H⁻ current at low H₂ pressure. Meanwhile, the beam current density has abruptly increased as the microwave discharge power was raised above 60 W, indicating a change of discharge mode around that input power.

Keywords

ion source, negative ion, electron cyclotron resonance, vibrationally excited molecule

DOI: 10.1585/pfr.8.2401035

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This paper may be cited as follows:

Motoi WADA, Tomoya ICHIKAWA, Toshiro KASUYA, Takahiro KENMOTSU, Masaki NISHIURA, Hiroshi TAKEMURA and Hitoshi YAMAOKA, Plasma Fusion Res. 8, 2401035 (2013).