Experimental study of a 1 MW, 170 GHz gyrotron with internal mode converter

Summary form only given. A high frequency gyrotron suitable for electron cyclotron heating (ECH) of the International Thermonuclear Experimental Reactor (ITER) is being investigated at MIT. Our goal is to demonstrate efficient operation at a power level in excel of 1 MW with a Gaussian output beam. The gyrotron is designed to operate in the TE/sub 28, 8/ mode at 170 GHz. A standard tapered cavity is used. A large input angle and short interaction length are chosen to avoid multimoding. Self consistent theory predicts 1.2 MW output power with 77 kV beam energy, 38 Ampere beam current for an efficiency of 45%. This efficiency is based on a beam with velocity ratio alpha of 1.66 and a perpendicular velocity spread of 10%. Taking into account the voltage depression 7 kV and an additional 10% loss, a final efficiency of 35% can be achieved. An electron gun is designed using the simulation code EGUN. Result of the simulation shows that the gun can produce electron beam with alpha of 1.7 and perpendicular velocity spread of 2.2% at 170 GHz. Even with additional spread due to the emitter temperature and surface roughness effects, we feel that total spread of 10% or less is possible.