FT/P2-26 Long Pulse/High Power ECRF System Development in JT-60U

Abstract. In the recent gyrotron development in JT-60U ECRF system, output power of 1.5 MW for 1 s has been achieved at 110 GHz. It is the world highest power oscillation in the range of > 1 s. In addition to the carefully designed cavity and collector in view of thermal stress, an RF shield for the adjustment bellows, and a low-dielectric-loss DC break enabled this achievement. Power modulation technique by anode voltage control was improved to obtain high modulation frequency and 5 kHz has been achieved for NTM stabilizing experiments. Moreover as a development step to realize a reliable ECRF system in future fusion experiments, long pulse demonstration of 0.4 MW, 30 s injection to the plasma has been achieved with real time control of anode/cathode-heater. It has been confirmed that the temperature of cooled components were saturated and no evidence of damage were found in the waveguides and antenna without forced cooling. As a forced cooling antenna for longer pulse in future, an innovative antenna having relatively wide range of beam steering capability with linearly-moving-mirror concept has been designed. Beam profile and mechanical strength analyses shows the feasibility of the antenna.