Field analysis of a novel interaction structure for high power sub-THz wave coaxial cavity gyrotrons

In this paper, a novel interaction structure for high power sub-THz wave coaxial cavity gyrotrons has been field-analyzed and mathematical formulation for its characteristic equation is presented. The proposed coaxial structure consists of an open-ended cavity resonator with a coaxial insert consisting triangular slots or corrugations. Surface Impedance Approach is followed for analysis purpose owing to its simplicity. Analysis has been done assuming the field inside the slots to be homogenous, which occurs when the number of slots is much higher than the azimuthal index of the mode. The presence of corrugations on the insert(inner rod) significantly alters the eigenvalues of the structure, which depends on the ratio of outer to inner radii(C=R₀/R_i) and by incorporating a tapered inner rod, quality factor of the desired and competing modes can be controlled which leads to better mode selection with reduced competition.