Progress on high power long pulse gyrotron development in JAEA

Recent progress of JAEA high power long pulse gyrotrons is reported. Multi-frequency oscillation and the high efficiency long distance power transmission were demonstrated at three frequencies, 170 GHz, 137 GHz and 104 GHz. The output power of 1 MW was obtained at three frequencies. The transmission efficiency from the gyrotron window to the end of the 40 m transmission line is 91 %, 89 % and 84 %, respectively. On the other hand, the dual frequency gyrotron of 138 GHz/110 GHz was developed for the application to the EC heating and current drive on JT-60SA tokamak. The power output of 1 MW/10 s and 0.5MW/198 s were demonstrated at both frequencies, and further pulse extension at 1 MW is underway aiming 100 s. For utilizing the triode characteristics, the gyrotron operation using the anode voltage control was demonstrated. Then, the main voltage and body voltage are kept constant, and the anode voltage is controlled. As a result, 5 kHz power modulation with very fast main mode excitation was demonstrated, which will be useful for the normal operation, high frequency modulation, and quick re-start up scenario after a power shut-off event. As for the ITER 1 MW 170 GHz gyrotron development, TE_{31, 9} mode gyrotron was fabricated and tested as a primary candidate of ITER gyrotron. In the short pulse operation, stable 1 MW output was obtained with the oscillation efficiency of 33 %. The pulse extension has started, and 0.61 MW/10 s output was obtained at the efficiency of 51 %, and the power increase and pulse extension are underway.