Improved Suppression of Parasitic Oscillations in Gyrotron Beam Tunnels by Proper Selection of the Lossy Ceramic Material

Abstract

Lossy dielectric materials are used in gyrotron beam tunnels to suppress possible parasitic oscillations by raising their starting currents. The dependence of the overall losses of the structure on the dielectric properties of the material is theoretically and numerically investigated and it is shown that materials with high values of the loss tangent are not suitable for the suppression of the parasitics. The beam tunnel is studied parametrically with a full-wave code, which calculates the diffraction and dielectric losses of the cold-cavity modes. A simplified geometry involving analytic relations is used to verify the results and investigate the underlying physics. It is shown that the proper selection of the material properties and its radial thickness can improve the absorption of the fields significantly.