A high power complex cavity gyrotron for fusion research devices

Gyrotron oscillators are of great interest as sources of high power mm wave radiation for electron cyclotron resonance heating and current drive in magnetic fusion research devices. However, as gyrotron power approaches the megawatt level, a very large, overmoded cavity must be employed in order to keep ohmic power losses in the cavity at an acceptable level, and the problem of mode overpopulation becomes severe. In this paper a novel approach for solving the problem by using a multiple, or complex cavity configuration is described. Prebunching is achieved in the first cavity while energy extraction takes place in the second. Experimental and theoretical studies for efficiency enhancement and mode competition reduction are presented for a 35 GHz, 350 kW gyrotron oscillator operating with a TE01/TE04cavity.