Plasma and Fusion Research
Online ISSN : 1880-6821
ISSN-L : 1880-6821
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Recent Studies of Hydrogen Negative Ion Source and Beam Production for NBI in Large Helical Device
Katsunori IKEDAShaofei GENGKatsuyoshi TSUMORIHaruhisa NAKANOMasashi KISAKIKenichi NAGAOKAMasaki OSAKABEOsamu KANEKOYasuhiko TAKEIRI
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2016 Volume 11 Pages 2505038

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Abstract

The state of hydrogen plasma in the extraction region in a hydrogen negative-ion (H) source for NBI has been investigated. We clearly observe an improvement of H density owing to the surface production effect with Cs seeding. H ions are widely distributed in the extraction region which is obtained by movable cavity ring down (CRD). We confirm a negative ion rich plasma with a few electrons in the extraction region, which state is important for reduction of electron contamination in extracting beam. An extraction area is reached 30 mm from the PG surface, which is measured by a 2D imaging diagnostic for Hα emission. We find the insensitive area for Hextraction at the PG surface between the apertures. Negative ions produced at the surface are considered to have been supplied in the extraction region. The flow velocity of H ions is obtained by a four-pin Langmuir probe using a photodetachment technique with an Nd:YAG laser. H ion flows from the plasma grid surface, and its direction drastically changes at 20 mm from the production surface. This flow behavior is considered to be an important characteristic for improving Hdensity in the extraction region.

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© 2016 by The Japan Society of Plasma Science and Nuclear Fusion Research
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