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Visualization of H⁻ Dynamics in Extraction Region of Negative-Ion Source by H_α Imaging Spectroscopy

Katsunori IKEDA, Haruhisa NAKANO, Katsuyoshi TSUMORI, Masashi KISAKI, Kenichi NAGAOKA, Masaki OSAKABE, Yasuhiko TAKEIRI and Osamu KANEKO

National Institute for Fusion Science, 322-6 Oroshi, Toki, Gifu 509-5292, Japan

(Received 14 December 2012 / Accepted 11 March 2013 / Published 23 April 2013)

Abstract

We developed a new imaging spectroscopy diagnostic tool for H_α emission and installed it on a negative hydrogen ion (H⁻) source to investigate the H⁻ dynamics in the extraction region. During beam extraction, the H_α emission dropped; the same drop also appeared in the H⁻ density (as measured by cavity ring-down spectroscopy). The reduction in the H_α emission results from the reduction in the excited hydrogen population caused by mutual neutralization processes between H⁺ and H⁻ ions, which in turn are due to a decrease in the H⁻ density. We find a reduction structure in H_α that is observed inside the plasma farther than 20 mm from the plasma grid (PG) surface. The result indicates that H⁻ ions produced at the PG surface accumulate in the extraction region, so we conclude that they flow toward the PG apertures.

Copyright (c) 2013 The Japan Society of Plasma Science and Nuclear Fusion Research

Keywords

negative ion source, H⁻, H_α, mutual neutralization, imaging spectroscopy

DOI: 10.1585/pfr.8.1301036

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References

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This paper may be cited as follows:

Katsunori IKEDA, Haruhisa NAKANO, Katsuyoshi TSUMORI, Masashi KISAKI, Kenichi NAGAOKA, Masaki OSAKABE, Yasuhiko TAKEIRI and Osamu KANEKO, Plasma Fusion Res. 8, 1301036 (2013).