Thermo-mechanical analysis of single-disc edge-cooled silicon nitride millimeter wave window for 200 kW CW gyrotrons

Abstract

This paper investigates the possibility of using Silicon Nitride Composite (Kyocera SN- 287) as single-disc, edge-cooled window for gyrotrons operating below 200 kW CW in the frequency range 28- 42 GHz. Rotationally symmetric TE0n and TEM00 Gaussian modes of rf transmission through the window have been considered. Analysis performed using a one dimensional (1D) finite difference (FD) code reveals that thermal stresses developed due to non-uniform temperature distribution on the disc surface are well within manageable limits for a 200 kW 42 GHz gyrotron proposed for some ECRH applications. For industrial gyrotrons, for microwave material processing and operating at a maximum power level of 100 kW CW, Si3N4 windows may be a cost effective replacement for sapphire windows. It is found that a TE02 profile results in lower peak temperature at the window disc in comparison to a Gaussian beam profile and allows the use of smaller discs.