Analysis of a Quasi-Optical Launcher Toward a Step-Tunable 2-MW Coaxial-Cavity Gyrotron

A high-efficiency quasi-optical launcher for coaxial-cavity gyrotrons has been investigated with the mode-matching analysis method. The launcher designed for the TE
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mode at 170 GHz is analyzed from 118 to 218 GHz with 67 modes. This investigation is a preliminary study of a launcher toward a step-tunable 2-MW coaxial-cavity gyrotron. Twenty-four modes with fundamental Gaussian mode content (FGMC) that is higher than 90% have been found. At last, nine modes of interest are selected for SURF3D simulations to investigate the transmission properties of millimeter-wave beams through the output window. The results reveal that the beams have deviations of their center points at the RF window within only 2.1 mm, and the FGMCs range from 92.67% to 96.67%. This result indicates that even the present launcher with specific deformations designed for only one mode would be capable of a step-tunable operation.