MEASUREMENT OF TEMPERATURE-DEPENDENCE OF DIELECTRIC PERMITTIVITY OF SAPPHIRE WINDOW FOR HIGH-POWER GYROTRONS

It was measured that the dielectric permittivity of sapphire window ch anged with temperature rise at the frequencies of 110.0 GHz and 170.0 GHz. The permittivity epsilon varied from 9.4 to 10.0 at 170.0 GHz wit h temperature rise from 300 K to 630 K, which can cause a significant rf reflection at the surface of the window and degrade gyrotron oscill ation. The permittivity change should be considered for the window des ign of high power, long pulse gyrotrons and transmission.