Density fluctuation measurement using motional stark effect optics in JT-60U

JT-60Uにおけるモーショナルシュタルク効果光学系を用いた密度揺動計測

鈴木 隆博; 藤田 隆明; 大山 直幸; 諌山 明彦; 松永 剛; 及川 聡洋; 朝倉 伸幸; 武智 学

Suzuki, Takahiro; Fujita, Takaaki; Oyama, Naoyuki; Isayama, Akihiko; Matsunaga, Go; Oikawa, Toshihiro; Asakura, Nobuyuki; Takechi, Manabu

JT-60Uでは中性粒子加熱ビームを利用したモーショナルシュタルク効果(MSE)偏光計により炉心プラズマ中の磁場分布を小半径の1/10程度の空間分解能で測定してきた。本研究ではMSE偏光計をビームエミッション光のモノクロメータとして使用することで可能になった高速揺動分布計測について報告する。空間的に局在化した不安定性による電子密度揺動分布やHモードプラズマのELMによる粒子の吐き出しが観測されている。

In JT-60U, we measure temporal evolution (100Hz) of the pitch angles of the magnetic field, using a 30 channel motional Stark effect (MSE) diagnostic with photo-elastic modulators (PEMs). This year, we started acquiring the signal intensity of photo-multipliers (PMs) at 0.5-1MHz sampling for fluctuation profile measurement. Response of the PM (180kHz/-3dB) limits the temporal resolution. The system works as the MSE and the beam emission spectroscopy (BES) diagnostic. Coupling between the MSE and BES signals can provide magnetic fluctuation. Here we report on results in spatially resolved electron density (ne) fluctuation profile measurement in various operation regimes. In the core plasma, ne fluctuation induced by rotating tearing mode islands was observed. Phase of the fluctuations are inverted between higher and lower magnetic field sides, which is consistent with an electron cyclotron emission (ECE) measurement. In the scrape-off layer of an ELMy -mode plasma, outward propagation of strong emission coincides with ELM crash was also observed. The propagation velocity is about 6km/s along the MSE measurement points, where distance between adjacent channels is 6-7cm in the major radius direction. Detailed description of the optics and the system will be presented.