CW, high power, gyrotron development at 110 GHz for ECH applications

Summary form only given, as follows. Electron cyclotron heating (ECH) is the most promising plasma heating method to achieve fusion. High-power, long-pulse or CW gyrotrons are required in many present and future ECH experiments. For example, the planned experiment at DIII-D, the experimental tokamak at General Atomics, will require 4 MW of RF power at 110 GHz for a pulse duration of 10 seconds. The RF requirement for the planned International Thermonuclear Experimental Reactor (ITER) is 50 MW at 170 GHz and CW operation. CPI is developing high-power, CW gyrotrons at frequencies ranging from 84-170 GHz for various ECH experiments. In particular, we are developing a 1 MW, CW gyrotron with an internal converter at 110 GHz. Recent results of the experimental, prototype tube included 1 MW for 2-ms pulses, 500 kW for 2-s pulses, and 350 kW for 10-s pulses. In addition, the tube was tested to average power levels of 100-150 kW. Peak temperature of the output window, which was measured by an infrared camera, limited the long-pulse power level. The limiting factor in CW operation was the over-heating of portions of the tube that were inertially cooled. To achieve the goal of 1 MW, CW operation, we have designed and begun fabrication of a new tube that has improved cooling to all tube parts which showed signs of overheating during the last experiment. In addition, we are looking at the possibility of using alternate output window designs to increase power handling capability.