Single-mode operation of a high-power, step-tunable gyrotron

This is the authors' abstract. We don't add key points for this paper.

A gyrotron oscillator with a single cylindrical cavity has produced output powers up to 645 kW and efficiencies up to 24% at 140.8 GHz, and step-tunable single-mode operation between 126 and 243 GHz. Mode stability and suppression of nearby competing modes are found to persist even for operation in very high-order cavity modes with severe mode competition. These results greatly improve prospects of developing cw megawat gyrotrons relevant to the heating of fusion plasmas.