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

JT-60Uにおける周辺電流駆動と電流分布制御

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; 武智 学; 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; Takechi, Manabu; Naito, Osamu; Hamamatsu, Kiyotaka; Sueoka, Michiharu; Hosoyama, Hiroki; Nakazato, Mikoto; JT-60 Team

モーショナルシュタルク効果偏光計を用い、中性粒子ビーム(NB)による周辺部駆動電流密度分布を初めて測定し、空間的に局在化していることを明らかにした。電流駆動位置は中性子分布計測と合致し、全駆動電流は表面の周回電圧の減少と合致する。周辺部での電流駆動はプラズマ中心部の安全係数を上げプラズマの性能を制限する不安定性を抑制することができる。LH波による周辺部電流駆動を用い、安全係数最小値(qmin)の実時間制御システムを開発した。本システムを高プラズマ(N=1.7, p=1.5)に適用し、qminを上昇させて不安定性を抑制した結果、蓄積エネルギーは16%上昇した。

For the first time, we have measured the current density profile for off-axis neutral beam current drive (NBCD), using motional Stark effect (MSE) diagnostic. A spatially localized NBCD profile was clearly observed at . The location was also confirmed by neutron emission profile measurement. The total amount of the driven current (0.15MA) was consistent with the decrease in the surface loop voltage. The off-axis current drive can raise safety factor (q) in the center and help to avoid instability that limits performance of the plasma. We have developed a real-time control system of the minimum q (qmin), using the off-axis current drive. Injection power of lower hybrid (LH) waves, and hence, its off-axis driven current controls qmin. In a high plasma (, ), the system was adopted to control qmin. With the control, qmin was raised and MHD fluctuations were suppressed. The stored energy increased by 16% with the MHD fluctuations suppressed.