Observation of plasma density oscillation with doubled value of RF frequency in J-PARC RF ion source

J-PARC高周波イオン源の2倍周波数でのプラズマ密度振動の観測

柴田 崇統*; 神藤 勝啓   ; 高木 昭*; 小栗 英知  ; 池上 清*; 大越 清紀 ; 南茂 今朝雄*; 内藤 富士雄*

Shibata, Takanori*; Shinto, Katsuhiro; Takagi, Akira*; Oguri, Hidetomo; Ikegami, Kiyoshi*; Okoshi, Kiyonori; Nammo, Kesao*; Naito, Fujio*

Balmer alpha line intensity in J-PARC Radio Frequency (RF) negative hydrogen ion source has been measured by photometry measurement. The line intensity shows several interesting time characteristics in different phases; (1) 2 MHz (RF frequency) oscillation just after plasma ignition and (2) 4 MHz (doubled RF frequency) and 2 MHz coupled oscillation in the steady-state. From the comparison between numerical analysis, it has been explained that electron acceleration in inductively coupled electromagnetic field takes place with 4 MHz frequency which results in the 4 MHz line intensity oscillation. From the understandings of the background physics, we can conclude that this fast photometry measurement is a good diagnosis tool to understand whether RF plasma is in E-mode or H-mode in general RF ion sources.