Design of a quasi-optical mode converter for a dual-frequency coaxial-cavity gyrotron

A quasi-optical mode converter is under development for an 170/204 GHz coaxial-cavity gyrotron at KIT, which is operated in the TE34,19 mode at 170 GHz and the TE40,23 mode at 204 GHz. A mirror-line launcher should be used for such modes with the ratio of caustic to launcher radius to be approximately 0.32. The optimum value of the launcher radius has been found to provide RF beams with relative high Gaussian-mode contents for both operation modes.