@article{oai:nifs-repository.repo.nii.ac.jp:00010701,
 author = {IKEDA,  Katsunori and GENG, Shaofei and TSUMORI,  Katsuyoshi and NAKANO,  Haruhisa and KISAKI,  Masashi and NAGAOKA,  Kenichi and NAGAOKA, Ken-ichi and OSAKABE,  Masaki and TAKEIRI,  Yasuhiko},
 issue = {Special Issue1-ITC25},
 journal = {Plasma and Fusion Research},
 month = {Apr},
 note = {0000-0002-0585-4561, 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 30mm from the PG surface, which is measured by a 2D imaging diagnostic for Hα emission. We find the insensitive area for H− extraction 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 20mm from the production surface. This flow behavior is considered to be an important characteristic for improving H− density in the extraction region.},
 title = {Recent Studies of Hydrogen Negative Ion Source and Beam Production for NBI in Large Helical Device},
 volume = {11},
 year = {2016}
}