High-Efficiency Oscillation of 170 GHz High-Power Gyrotron at TE_31,8Mode Using Depressed Collector

Abstract

Stable 1.1 MW oscillation was achieved by a 170 GHz high power gyrotron. The oscillation mode capable of the CW operation is TE 31,8 . The efficiency was 32%, which was enhanced to 57% by a depressed-collector operation. The parasitic oscillation in a beam tunnel (a beam drifting tube between an electron gun and a cavity) that degraded the oscillation efficiency was suppressed by installing an RF absorber. This result has a large impact on the development of a 1-MW-long-pulse gyrotron that is required for fusion devices.