Design of Quasi-optical Mode Converter for 800-GHz TE8,5 Mode Gyrotron

Due to operating in high-order rotating modes, the electromagnetic waves generated by the gyrotron cannot be transmitted over long distances in space. So the adoption of quasi-optical mode converters is necessary to transform these waves into linearly polarized Gaussian beams with reduced transmission losses. To improve the efficiency of designing and optimizing the high-frequency quasi-optical mode converter, we propose a fast integration algorithm based on scalar diffraction theory. In this paper, a quasi-optical mode converter for 800GHz TE
8,5
mode gyrotron is designed in Wuhan National High Magnetic Center (WHMFC). The mode converter consists of a Vlasov launcher and a mirror system, which includes a quasi-elliptical mirror and a parabolic mirror, focusing the radiation field into a Gaussian beam. A MATLAB code based on scalar diffraction theory is developed to analyze the electromagnetic field distribution on the launcher aperture and mirror system. The code is used to calculate the field distribution on the observation plane of a 263GHz, TE
3,2
mode gyrotron launcher, and the results are compared with the simulation software FEKO. The findings show a vector correlation coefficient exceeding 95%, validating the accuracy of the developed program. More importantly, the computation time is shortened by over a thousand times compared to the latter. The calculation results demonstrate a scalar Gaussian content of 94.25% on the output window.