Recent ITER-Relevant Gyrotron Tests

Recent tests of two different megawatt-class gyrotrons at CPI provide a design baseline for the 120 GHz, 1 MW CW gyrotrons required by ITER for plasma start-up. The two gyrotron designs include a 140 GHz, 900 kW CW device that was delivered to the Max Planck Institute for Plasma Physics in Greifswald, Germany, and a 110 GHz, 1.3 MW CW gyrotron that was recently tested at CPI. Both gyrotrons utilize many of the same features that are foreseen for the ITER 120 GHz gyrotrons. These features include: single-anode magnetron injection electron guns, high-efficiency internal converters that produce a pure TEM00 output mode, 88-mm-diameter diamond output windows and single-stage depressed collectors. In tests at CPI, the 140 GHz gyrotron achieved 500 kW power levels for 700-s pulses and 930 kW for short pulses. Long-pulse tests of the gyrotron, at beam currents above the 25-A test-set limit at CPI, were performed in Greifswald and resulted in output power levels of up to 900 kW for 30-minute pulses. In short-pulse operation at CPI, the 110 GHz gyrotron has achieved power levels of 1.28 MW. In long-pulse tests of the gyrotron, power levels of 500 kW were obtained for 10-s pulses