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Alfv$'e$n eigenmodes in reversed shear plasmas in JT-60U negative-ion-based neutral beam injection discharges

JT-60Uの負イオン源中性粒子入射加熱負磁気シアプラズマにおけるアルフベン固有モード

武智 学; 福山 淳*; 石川 正男; Cheng, C. Z.*; 篠原 孝司; 小関 隆久; 草間 義紀; 竹治 智*; 藤田 隆明; 及川 聡洋; 鈴木 隆博; 大山 直幸; 森岡 篤彦; Gorelenkov, N. N.*; Kramer, G. J.*; Nazikian, R. M.*; JT-60チーム

Takechi, Manabu; Fukuyama, Atsushi*; Ishikawa, Masao; Cheng, C. Z.*; Shinohara, Koji; Ozeki, Takahisa; Kusama, Yoshinori; Takeji, Satoru*; Fujita, Takaaki; Oikawa, Toshihiro; Suzuki, Takahiro; Oyama, Naoyuki; Morioka, Atsuhiko; Gorelenkov, N. N.*; Kramer, G. J.*; Nazikian, R. M.*; JT-60 Team

JT-60Uの負磁気シア(RS)及び弱磁気シアプラズマ(WS)におけるアルフベン固有モード(AE)実験の結果について報告する。低$$beta$$hのRS放電において負イオンNBI(NNBI)及びICRFによって加熱中に観測された急激な周波数の掃引を伴うモードは負磁気シア励起AE(RSAE)とこのRSAEからトロイダルAE(TAE)への遷移によって説明可能である。われわれはJT-60Uにおいて磁気揺動の観測と安全係数分布の計測を行い、RSAEの存在とRSAEからTAEへの遷移を初めて証明した。中性子発生率の計測によってRSAEからTAEへ遷移時に高速イオンが吐き出されることが明らかになった。

Rapid frequency sweeping modes observed in reversed magnetic shear (RS) plasmas on the Japan Atomic Energy Research Institute Tokamak 60 Upgrade (JT-60U) have been identified as Reversed-Shear-induced Alfv$'e$n Eigenmodes (RSAEs), which are ideal MHD Alfv$'e$n eigenmodes (AEs) localized to the region of minimum safety factor, $$q_{rm min}$$, and are excited by negative-ion-based neutral beam injection. The chirping and subsequent saturation of the mode frequency are consistent with theoretical predictions for the transition from RSAEs to Toroidal Alfv$'{e}$n eigenmodes (TAEs). The previously observed rapid frequency sweeping modes in ion cyclotron wave heated plasmas in JT-60U can also be similarly explained. The observed AE amplitude is largest during the transition from RSAEs to TAEs, and fast ion loss is observed when the AE amplitude is largest at this transition. It is preferable to operate outside the transition range of $$q$$$$_{min}$$, e.g., 2.4 $$<$$ $$q$$$$_{min}$$ $$<$$ 2.7 for the n = 1 AE to avoid substantial fast ion loss in RS plasmas.

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パーセンタイル:29.16

分野:Physics, Fluids & Plasmas

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