Long pulse operation of a dual frequency gyrotron for JT-60SA

Long pulse operation of a dual frequency gyrotron for JT-60SA, which can oscillate both 110 GHz and 138 GHz waves, was started. Oscillations at ∼ 0.4 MW for 2 s (both frequencies) and 0.7 MW for 1 s (110 GHz) were obtained, so far. Temperature increase in the cavity, the output window and some components, which absorb stray radiation in the gyrotron, were measured and cavity loss power and the dielectric loss tangent of the output window were evaluated. Heat loads in the gyrotron measured so far were acceptable for long pulse operation at an output power of 1 MW.