Development of 170 GHz/1 MW/ 50%/CW gyrotron for ITER

Recent test results of 170 GHz/1 MW/CW gyrotron being developed in Russia within the ITER program are presented. At pulse duration of 0.1 s, power of 1.15 MW in the output Gaussian beam was attained. In the experiments on pulse extension, output power was not so large considering performance capabilities of high voltage source. At output power of 0.85-0.9 MW, the gyrotron pulse could be extended to nearly 20 s. At the power reduced to 0.7 MW, pulse lasted up to 42 s. Pulse duration of 80 s reached in 2002 at 0.5-MW output power was not managed to exceed this time due to similar external limitations. It turned out that transmission line elements rather than gyrotron itself were responsible for pulse limitation. Presently, the work is carried out to overcome the circuit imperfection. To provide gyrotron reliable CW run, present level of stray radiation is to be sufficiently lowered. Denisov converter adapted for TE_25.10 mode operation at 170-GHz frequency and designed to reduce the stray radiation fraction from 11% to less than 3% of generated power is used in modified gyrotron. New converter was embedded in short-pulse gyrotron mock-up and tested. Long-pulse gyrotron test is planned to the end of the year. Searching ability to have higher power design of 2 MW/170 GHz/CW gyrotron has been started. Short-pulse mock-up is tested in the current year and long-pulse gyrotron prototype can appear in 2005.