A Compact Dual-Mirror Design of Quasi-Optical Mode Converter for Gyrotron Application

The quasi-optical mode converter (QOMC) for high-power fusion gyrotron is a typical beam transformation and shaping device in near-field region. In this letter, the authors report their progress in designing a compact QOMC with only two reflecting mirrors. For achieving the high-efficiency conversion comparable to conventional multimirror converters, the authors exercise modification and optimization on the first mirror based on the classic quasi-elliptical design. It is shown that the optimized first mirror can fulfill multifunctions that have to be achieved by a chain of mirrors in conventional designs. Numerical results show the effectiveness of the optimization, which can be revealed by the achieved 95.97% Gaussian content in the output beam with power transmission efficiency of 99.0%.