Pedestal characteristics in JFT-2M HRS H-mode plasma

JFT-2M HRS Hモードプラズマのペデスタル特性

神谷 健作; 大山 直幸; 三浦 幸俊; Hubbard, A. E.*

Kamiya, Kensaku; Oyama, Naoyuki; Miura, Yukitoshi; Hubbard, A. E.*

JFT-2Mでは今回プラズマ周辺部のパラメータを詳細に調べ、HRS Hモードの運転領域をペデスタルパラメータの観点から調べた。HRS Hモードはプラズマ周辺部のパラメータが高密度・低温状態で観測され易く、低密度・高温状態では大振幅のELMが発生した。密度,温度、及び安全係数をスキャンした結果、プラズマ周辺部の規格化衝突周波数e*(neq95/Te2)が運転領域を決定する重要なパラメータの一つであることが示唆され、ELMy/HRS運転領域境界はe*が1付近に存在することがわかった。

Recent experiments in the JFT-2M tokamak have concentrated on the studies of the access condition for the H-mode operation without any large ELMs, namely High Recycling Steady (HRS) H-mode regime in terms of the pedestal parameters. The HRS regime is more likely at the higher edge density and lower edge temperature, while the ELMy H-mode having large ELMs appears at the lower edge density and higher edge temperature. It is found that the ELMy/HRS operational boundary occurs at the normalized electron collisionality of *1 in the plasma edge region, depending slightly on q. A key feature of the HRS H-mode is the presence of the coherent magnetic fluctuations in the frequency range of the order of 10-100 kHz. It is suggested that the edge MHD activities may keep an edge pressure below a certain level needed to induce a large ELM.