Thermo-Mechanical Analysis and Its Effect on Rf Behaviour of A Tapered Cavity of the W-Band Gyrotron Oscillator

Abstract

Thermo-mechanical analysis of a tapered cylindrical RF interaction cavity of a TE6,2, 95 GHz, 100 kW gyrotron has been carried out to study the effect of ohmic loss generated due to radiated microwave energy. For stable device operation, with the help of design relationships, describing the approach, an optimum thermal system design has been presented and performances got analyzed using a commercial simulation code “COMSOL Multiphysics”. For various cavity thicknesses, and convective heat transfer coefficient values under without fins and with radial fins conditions system performance have been investigated. Taking water as coolant at ~293 K, hydraulic diameter and flow rate range has been determined for the optimum convective heat transfer coefficient values. An optimized simple cooling system thus designed keeps the maximum RF cavity radius deformation (increase) ~ 3.2 µm maintaining the average cavity outer surface temperature of 308 K. Further, using nonlinear time-dependent multimode analysis, a decrease of 48 MHz in resonance and a decrement of 20 in diffractive quality factor of the interaction cavity along with reduction of 2 kW of the device output power have been observed in the case for the deformed cavity from those of the initial cavity gyrotron device, which are found within the tolerance limit of such devices.