RF and Thermal Analysis of Beam Compression Unit for a $W$ -Band Gyrotron

Abstract

A four-section beam compression unit (BCU) with copper and aluminum nitride–silicon carbide (AlN-SiC) annular disks was proposed for a $W$ -band gyrotron. Various dimensional parameters were calculated, based on which the BCU was modeled in a high-frequency structure simulator (HFSS), and the transmission characteristics were plotted for various sets of dimensional parameters. The dimensional parameters were optimized for achieving the attenuation of more than 60 dB over 85–105 GHz. It was further examined that the hollow electron beam radius over various sections of the BCU should not lead to beam–wave interaction, and if so, it should not propagate toward the interaction cavity. For this purpose, azimuthal electric field intensities in various azimuthally symmetric modes below the operating mode were plotted against the radial coordinate in various sections of the BCU and checked for the azimuthal electric field intensity values with the range of beam radius in the corresponding section. The electric field intensity maxima should be avoided within the range of beam radius in the corresponding section. Furthermore, the transient thermal analysis of the BCU was carried out considering temperature varying thermal conductivity in two proposed models: 1) with radially constant and 2) radially varying heat loads within AlN-SiC disks to predict the maximum temperature attained in the ceramic as 76.8 °C and 88.5 °C, respectively, taking 8-L/min flow rate of deionized water and ten heat load pulses.