A new method for the design of quasi-optical launchers for high power gyrotrons

A numerical method has been developed for the analysis of the fields on highly oversized waveguide launcher walls with arbitrary deformations, where the ratio of launcher diameter to wavelength is larger than 10, and the perturbations of the launcher wall surfaces are shallow and smooth. Based on the analysis method, an iterative algorithm for synthesizing the launcher wall structure has been developed to achieve a high correlation coefficient of the outgoing wave beam to the desired distribution. As an example, a 309.6mm long waveguide launcher has been designed for a 170GHz coaxial-cavity gyrotron to transform the TE_34.19 cavity mode to a fundamental Gaussian distribution. An efficiency of transformation to the desired fundamental Gaussian mode of 96.3% has been obtained at the launcher aperture.