The Research and Design of Quasi-Optical Mode Converters Mirror System

The quasi-optical mode converters (QOMC) is the key device to improve the efficiency of high-power fusion gyrotron transmission. In this work, the authors report an efficient QOMC design for a compact three-mirror layout in 140 GHz, TE22,8. Based on geometrical optics and iterative phase correction technique, the design of the first-stage focusing mirror and the second and third-stage phase mirrors is completed. The full vector physical optics integration is adopted as the main computational means, and the three-level phase correction surface is iterative optimized around the main polarization field component to realize the mode field conversion with high outgoing Gaussian purity. The outgoing Gaussian purity μv of the phase-corrected converter system is improved from 94.1% to 99.7%, which, combined with a power transfer efficiency μp of more than 98.7%, realizes a high-performance prototype design of a higher-order cyclotron QOMC.