Demonstration of high-power gyrotron operation at 203 and 236 GHz toward future fusion devices

Abstract Gyrotrons having a high output-frequency of more than 200 GHz will be necessary for future fusion devices, such as the DEMO reactor. At 170 GHz, gyrotrons for ITER achieved a high power of 1 MW with a high electrical efficiency of approximately 50% (oscillation efficiency of approximately 30%) in a long pulse operation. At frequencies higher than 200 GHz, no gyrotrons have achieved ITER-like performance, which this study attempted to demonstrate using a prototype multi-frequency gyrotron for 170 GHz, 203 GHz, and 236 GHz. At 203 GHz, an output power of 0.87 MW was achieved at the gyrotron window with an oscillation efficiency of 25% and an electrical efficiency of 41% in a long pulse operation of 100 s. Although this performance is lower than that of the ITER gyrotrons at 170 GHz, this study represents the first demonstration that ITER-like performance is achievable at frequencies above 200 GHz. In addition, short 1 ms pulse tests at 236 GHz achieved an output power of 1 MW.