Recent RF experiments and application of RF waves to real-time control of safety factor profile in JT-60U

JT-60Uにおける最近の高周波加熱実験及び高周波の実時間安全係数分布制御への応用

鈴木 隆博; 諫山 明彦; 井手 俊介; 藤田 隆明; 及川 聡洋; 坂田 信也; 末岡 通治; 細山 博己*; 関 正美; JT-60チーム

Suzuki, Takahiro; Isayama, Akihiko; Ide, Shunsuke; Fujita, Takaaki; Oikawa, Toshihiro; Sakata, Shinya; Sueoka, Michiharu; Hosoyama, Hiroki*; Seki, Masami; JT-60 Team

JT-60において、低域混成波による電流駆動とモーショナルシュタルク効果による安全係数分布計測を用いた実時間安全係数分布制御システムを開発した。実時間制御のクロックである10ms以内で安全係数分布を高速に評価するための計算手法を開発し、精度よく安全係数分布を計算できることを示した。低域混成波の位相制御により電流駆動位置を制御した。中心での安全係数の正磁気シアプラズマを対象にの正磁気シア安全係数分布を目標として制御を行ったところ、安全係数分布は目標分布に近づき、の状態を低域混成波が安定に入射されている間(3秒間)維持した。電子サイクロトロン波による新古典テアリングモードの安定化及び、プラズマの着火・立ち上げについても本招待講演において報告する。

A real-time control system of safety factor (q) profile was developed in JT-60. This system, for the first time, enables 1) real time evaluation of q profile using local magnetic pitch angle measurement by motional Stark effect (MSE) diagnostic and 2) control of current drive (CD) location (rhoCD) by adjusting the parallel refractive index of lower-hybrid (LH) waves through the change of phase difference (dphi) of LH waves between multi-junction launcher modules. The method for q profile evaluation was newly developed, without time-consuming reconstruction of equilibrium, so that the method requires less computational time. The system evaluates q profile within every 10ms, which is much faster than current relaxation time, typically order of 1s. Safety factor profile by the real-time calculation agreed well with that by equilibrium reconstruction with MSE. From temporal evolution of q (or current) profile, we evaluate CD location in real-time, too. The control system controls rhoCD through (or directly dphi) in such a way to minimize difference between the real-time evaluated q profile and its reference profile. The real-time control system was applied to positive shear plasmas (), having plasma current of 0.6MA, toroidal field of 2.3T, and electron density of . In order to keep good coupling of LH waves to the plasma, gap between the launcher and the plasma surface was controlled to about 0.1m. The reference q profile was set to q(0)=1.3. The real-time q profile approached to the reference after application of real-time control; the controlled q profile was sustained for 3s, which was limited by injected LH power. RF experiments in JT-60U, such as stabilization of neo-classical tearing modes, plasma startup experiments, etc., are also presented.