Analysis of the Possibilities to Control Diffraction Quality Factors of the Cavities of Subterahertz Gyrotrons

Abstract

Manufacturing of cylindrical cavities for short-wavelength gyrotrons is usually performed with micrometer-scale precision. In subterahertz (sub-THz) and terahertz (THz) gyrotrons, this often results in the fabrication of slightly up-tapered cavities instead of the cavities having the central parts of a constant radius. Correspondingly, the diffractive quality factors ( $Q_{\mathrm {D}}$ -factors) of such slightly conical cavities may differ from those calculated for the cavities with constant radius central parts. We show that the sensitivity of $Q_{\mathrm {D}}$ -factors to the cavity fabrication can be mitigated by introducing some local nonuniformities at the end of a slightly conical up-tapered section of the cavities. The proposed approach is illustrated with an example of a gyrotron designed for spectroscopic applications and having an output radiation power of tens of watts at the frequency of 0.527 THz. This article presents some numerical modeling results, which show how proposed local nonuniformities reduce the sensitivity of $Q_{\mathrm {D}}$ -factors to defects in fabrication.