Analysis of Plasma Loaded Conventional and Coaxial Cavity With Wedge-Shaped Corrugations on the Insert

Abstract

Mathematical analysis of plasma loaded coaxial cavity with wedge-shaped corrugations on the insert has been undertaken. Ideally, inside gyrotron cavity, there should be a perfect vacuum. However, such an absolute vacuum condition is never achieved as scant amount of gas is always left in the cavity, which leads to the creation of plasma. This makes plasma analysis necessary for gyrotron interaction structure design. In a plasma-loaded waveguide, three families of modes can propagate-space charge modes, cyclotron modes, and waveguide EH and HE modes. The presence of magnetized plasma leads to the coupling of two families of modes. In gyrotron cavity, the desired HE mode couples with the cyclotron mode. In this paper, field analysis of plasma-loaded corrugated coaxial cavity is undertaken without ignoring the coupled cyclotron mode. This coupling leads to shift in eigenvalues of the modes. Considering the plasma coupling effect inside gyrotron cavity, diffractive quality factor of the desired mode is calculated for the coaxial case and also for the conventional case. The conventional case is included to provide a better understanding of quality factor calculation for coaxial case and present a generalized conclusion for the effect of plasma on gyrotron operation. The results predict that the diffractive quality factor and the frequency of oscillation in a plasma cavity reduce as compared to the vacuum case.