The Quasioptical Gyrotron, A High-Power, Tunable Source of Millimeter-Wave Radiation

ABSTRACTThis talk will summarize the present state of the art of the quasioptical gyrotron (QOG), an alternative gyrotron configuration which has been under development primarily in the U.S. and Switzerland for heating fusion plasmas in tokamaks and other high-power millimeter-wave applications. The QOG features an open-mirror Fabry-Perot resonator instead of the conventional waveguide cavity used in conventional gyrotrons. This gives the QOG the potential for wide tunability, advantages for high-power operation, and facilitates the use of a depressed collector for spent electron beam energy recovery. An experimental QOG has been tuned from 85 to 130 GHz by varying the applied magnetic field. QOGs have produced peak powers up to 600 kW for 13 μs pulses and 100 kW for 10 ms pulses. Electronic efficiencies up to 22% have been achieved at 85 GHz, and operation with a depressed collector yielded an overall efficiency of 30%. The design of a multi-kW CW QOG tunable from 80 to 120 GHz is discussed.