Power modulation by changing anode voltage of the 110GHz-gyrotron on JT-60U ECH system

Terakado, Masayuki; Seki, Masami; Shimono, Mitsugu; Igarashi, Koichi*; Mitsunaka, Yoshika*; Isayama, Akihiko; Anno, Katsuto; Ikeda, Yoshitaka

The Electron Cyclotron Range of Frequencies (ECRF) system having four 110 GHz-gyrotrons has been successfully operated on JT-60U to locally heat a plasma (ECH) and drive a plasma current (ECCD) for high plasma performance owing to suppressing MHD activities. For investigation of plasma confinement the ECRF power is intermittently injected into plasmas to evaluate thermal conductivity. We have successfully performed power modulation by changing the anode voltage. The power modulation ratio of 80 % is attained changing the anode voltage by only about 10%. Modulation frequency is from 12 Hz to 500 Hz. The mode converter is heated when oscillation efficiency of the main mode decreases in changing the anode voltage. This seems to be due to the parasitic oscillation at the entrance of the converter. The gyrotron will be able to be protected by monitoring the temperature rise in the converter.