Study Of High Efficiency Mirror System For Millimeter Wave High Power Gyrotron

As a high power microwave source, gyrotron can provide high power electromagnetic energy in millimeter wave and sub-millimeter wave. They have been widely used in plasma heating of the controlled thermonuclear fusion, directed energy weaponry,advanced material processing, etc. Mirror system of quasi-optical mode converters, one of the key parts of high power gyrotron, can employ to transform high output power into Gaussian mode, which enables long distance transfer of gyrotron,conductive to its better stability and enhanced efficiency. Extensive and in-depth researched on mirror system of quasi-optical mode converters have been conducted by researchers from foreign countries in areas of basic theories, simulating calculation and engineering tests, whereas such researches are relatively few in China. In this background, this thesis concentrates on the theoretical studies, structural design and numerical modeling for the mirror system of quasi-optical mode converters. The main work of the thesis are as follows:1. Detailed theoretical analysis is conducted to mirror system of Vlasov-type quasi-optical mode converter. A theoretical calculation model on step-cut launchers and mirror system is given by geometrical optical. Design approaches of symmetrical mirrors in quasi-optical mode converters are investigated in detail. The simulation code is development and used in numerical for TE03 mode quasi-optical converter with two mirrors in the design of 95 GHz, which shows Guassian mode content of output beam reaches 98%, power transfer efficiency of mirror system surpasses 97% and mode converter efficiency stands at 84.86%.2. The simulation code considering the demand of TE28,8 mode for 140 GHz gyrotron is written, which is compared to the design parameters and experimental results reported in literature for its validity. Principal of phase correction and mirror system design approach is investigated. A code is written according to K-S algorithm based on error control for phase correction mirror. Optimization of design parameters is given via iterative algorithm to achieve respective fundamental Gaussian mode vector content from 90.2% to 92.9%, which substantially improves output beam quality.3. Using the simulation code, the introduction of new structure of the launcher disturbance is designed for TE28,8 mode four-mirror and three-mirror system of Denisovtype quasi-optical mode converter. Numerical simulation of launchers and mirror system are applied. Detailed analysis of TE28,8 mode to Gaussian beam conversion and quantitative analysis of the quality of output Gaussian beam from quasi-optical mode converter is provided. The results reveal power loss of mirror system is below 2%,fundamental Gaussian mode vector and scalar content of output beam reaches 95% and98% respectively, and mode converter efficiency is higher than 90%.