EXPERIMENTAL-STUDY OF HIGH-POWER MILLIMETER-WAVE TRANSMISSION OF SAPPHIRE WINDOW FOR ELECTRON-CYCLOTRON RANGE OF FREQUENCIES SYSTEM

The possibility of use of a sapphire disk as an output window of a hig h-power and long-pulse gyrotron was investigated using an RF test faci lity with high-power gyrotrons. The dielectric loss tangents, tan delt a = 1.8 x 10(-4) (T/300)(1.3+/-0.1) for 110 GHz and tan delta = 2.6 x 10(-4) (T/300)(1.3+/-0.1) for 170 GHz (T: absolute temperature in K), were obtained in the temperature range of 300 K to 600 K, The experime ntal results showed that RF reflection from the window became large du e to the permittivity change with increasing temperature, which limits the applicable power for the sapphire window rather than the thermal runaway. Moreover, it was found that a 170 GHz, 1 MW, CW gyrotron is f easible using a two-port window system consisting of sapphire double d isks more than 18 cm in diameter with a flat RF power profile.