Design of Quasi-Optical Mode Converter for 170-GHz TE32,9-Mode High-Power Gyrotron

In this paper, a design of quasi-optical mode converter for 170-GHz TE32,9-mode high-power gyrotron is presented in detail. The quasi-optical mode converter consists of a launcher and a mirror system. A MATLAB code for analysis of the electromagnetic fields at the launcher wall and in mirror systems has been developed. The numerically optimized launcher can generate a Gaussian-like mode with a scalar correlation coefficient of 99.6% and a vector correlation coefficient of 99.1% at the launcher aperture. The radiation fields of the launcher are analyzed in the free space. The mirror system consists of four analytic surface mirrors and a phase-correction mirror. After the phase correction, the scalar Gaussian mode content and vector Gaussian mode content on the output window are 99.1% and 97.1%, respectively. The performance of the mirrors is calculated and analyzed. The power transmission efficiency of each mirror is above 99.8%, and the efficiency of the quasi-optical mode converter is 96.77%.