Investigation of an advanced quasi-optical mode converter for a coaxial gyrotron

A quasi-optical mode converter is investigated for a 170 GHz, TE/sub 34.19/ mode coaxial-cavity gyrotron, where the ratio of caustic to cavity radius is 0.323. The dimpled-wall launcher is numerically analysed and optimised to provide a wave beam with scalar Gaussian contents of 94.8% and well-focused field at its aperture. The mirror system is adapted to transform the complicated fields radiated from the launcher into a fundamental Gaussian structure. The tolerance conditions of the mirror system to fabrication errors are also investigated. The achieved conversion efficiency is 97% including amplitude and phase.