Development of power modulation on JT-60U ECRF system

Kobayashi, Takayuki; Isayama, Akihiko; Terakado, Masayuki; Sato, Fumiaki; Sawahata, Masayuki; Suzuki, Sadaaki; Hiranai, Shinichi; Igarashi, Koichi; Wada, Kenji; Shimono, Mitsugu; Hasegawa, Koichi; Yokokura, Kenji; Shibayama, Minoru; Shinozaki, Shinichi ; Moriyama, Shinichi

It is recognized that stabilization of neoclassical tearing mode (NTM) instabilities using power modulated electron cyclotron current drive (ECCD) is effective. Although a modulation frequency of around 5 kHz was required to NTM suppression experiments in JT-60U, the achieved frequency had been limited to 3 kHz due to the slow response time of the high voltage circuit and over-current during charging/discharging. In this study, the anode voltage divider of the system was improved and the capacitance and resistance in the high voltage circuit was optimized resulting in the modulation frequency of over 5 kHz. The robust modulated operation region was also studied with suppressing undesired mode. Moreover, the real-time synchronizing system was developed to control the phase and duty ratio of the modulated ECCD synchronizing with the NTM frequency which varies during ECCD with plasma rotation, and modulated ECCD experiments with NTM suppression was carried out in JT-60U.