title: Effect of high-energy neutral particles on extreme ultraviolet spectroscopy in large helical device.
abstract: Spectra measured by an extreme ultraviolet (EUV) spectrometer frequently suffer large spike noise when Large Helical Device is operated in low-density range (≤ 3 × 10(13) cm(-3)) with neutral beam injection (NBI). The spike noise completely disappears in electron cyclotron heating discharges. In order to examine the effect of NBI, a carbon filter with thickness of 150 nm was installed in the EUV spectrometer. As a result, the spike noise was reduced by an order of magnitude. It is experimentally verified that the spike noise is caused by escaping high-energy neutral particles resulting from the circulating high-energy hydrogen ions borne from NBI.
authors.affiliation: National Institute for Fusion Science, Toki 509-5292, Gifu, Japan. dong.chunfeng@nifs.ac.jp
authors.forename: Chunfeng
authors.initials: C
authors.lastname: Dong
authors.forename: Shigeru
authors.initials: S
authors.lastname: Morita
authors.forename: Masayuki
authors.initials: M
authors.lastname: Tokitani
authors.forename: Motoshi
authors.initials: M
authors.lastname: Goto
authors.forename: Hiroyuki
authors.initials: H
authors.lastname: Sakaue
authors.forename: Erhui
authors.initials: E
authors.lastname: Wang
authors.forename: Hideki
authors.initials: H
authors.lastname: Zushi