Off-axis current drive and real-time control of current profile in JT-60U

JT-60Uにおける周辺部電流駆動と電流分布の実時間制御

鈴木 隆博; 井手 俊介; 及川 聡洋; 藤田 隆明; 石川 正男; 関 正美; 松永 剛; 波多江 仰紀; 内藤 磨; 濱松 清隆; 末岡 通治; 細山 博己; 中里 命; JT-60チーム

Suzuki, Takahiro; Ide, Shunsuke; Oikawa, Toshihiro; Fujita, Takaaki; Ishikawa, Masao; Seki, Masami; Matsunaga, Go; Hatae, Takaki; Naito, Osamu; Hamamatsu, Kiyotaka; Sueoka, Michiharu; Hosoyama, Hiroki; Nakazato, Mikoto; JT-60 Team

高プラズマにおいて高い閉じ込めと安定性のための電流分布の最適化を目指して、周辺電流駆動を用いた安全係数最小値の実時間制御システムを開発した。低域混成波の入射パワーを制御することで、時間的に変化する目標値にそってを1.3から1.7まで制御した。本制御を新古典テアリングモード(NTM)のある高放電に適用したところ、安全係数最小値が2を超えたときにNTMと共鳴する磁気面が消えてNTMは安定化され蓄積エネルギーは16%上昇した。さらに、周辺部での中性粒子ビーム電流駆動(NBCD)による駆動電流分布を初めて測定した。モーショナルシュタルク効果計測によると駆動電流は周辺部に空間的に局在しており、中性子放出分布計測によっても同様の結果を得た。NBCD電流総量はACCOMEコードによる理論計算と合う一方で、電流駆動位置は計算結果より外側にずれていることが明らかになった。

Aiming at optimization of current profile in high-b plasmas for higher confinement and stability, a real-time control system of the minimum of the safety factor () using the off-axis current drive has been developed. The off-axis current drive can raise safety factor in the center and help to avoid instability that limits performance of the plasma. The system controls injection power of lower-hybrid (LH) waves, and hence, its off-axis driven current in order to control . The real-time control of is demonstrated in a high- plasma, where follows the temporally changing reference from 1.3 to 1.7. Applying the control to another high- discharge (=1.7, =1.5) with =2/1 neo-classical tearing mode (NTM), was raised above 2 and the NTM was suppressed. The stored energy increased by 16% with the NTM suppressed, since the resonant rational surface was eliminated. For the future use for current profile control, current density profile for off-axis neutral beam current drive (NBCD) is for the first time measured, using motional Stark effect (MSE) diagnostic. Spatially localized NBCD profile was clearly observed at the normalized of about 0.6-0.8. The location was also confirmed by multi-chordal neutron emission profile measurement. The total amount of the measured beam driven current was consistent with the theoretical calculation using the ACCOME code. The CD location in the calculation was inward-shifted than the measurement.