Reseach And Design Of The Quasi-optical Mode Converter

At present, International Thermonuclear Experimental Reactor(ITER) program is one of the promising ways for solving the energy problem. ITER employs high power gyrotron oscillator as the microwave source for Electron Cyclotron Resonance Heating(ECRH). However high power gyrotrons for heating the plasma operate with high order mode, which are not suitable for propagation in free space. Thus quasi-optical mode is needed to convert high order mode into Gaussian beam. Quasi-optical mode converter composed by the launcher and mirrors. Launcher is classified with Vlasov launcher and Denisov launcher. Mirror can be is classified with normal and phase-correcting mirror. In this thesis, a comprehensive and systematic investigate on the quasi-optical mode converter for the gyrotrons operation on 140 GHz, TE28,8 mode and 94 GHz, TE6,2 mode, based on the domestic research, fabrication and the experimental feasibility to design a variety of quasi-optical mode converter systems, and the design of quasi-optical mode converter system to maintain consistency in the software simulation and experimental verification. The main research content includes five parts.1. The Vlasov launcher has been researched carefully. First derive the transverse electric mode(TE mode) and transverse magnetic mode(TM mode) in the waveguide propagation, and then using Geometric Optics theory to analyze microwave propagation in the waveguide. The Vlasov launchers were designed for 140 GHz, TE28,8 mode and 94 GHz, TE6,2 mode, which are easy to fabricate.2. Analysis of the Gaussian beam propagation properties in the free space, calculated six electromagnetic fields distribution of the Gaussian beam and elliptical Gaussian beam. Next step design of the phase-correcting mirror using the vector diffraction theory method.3. Using the vector diffraction theory to design and optimize normal mirrors. The quasi-optical mode converter system including two mirrors is designed for 140 GHz, TE28,8 mode, whose power transfer efficiency reaches to 89.03%; The power transfer efficiency of the quasi-optical mode converter system for 94 GHz, TE6,2 mode reaches to 87.10%, and the heat measured by experiments confirmed the correction of the design, while the design of a three-mirror quasi-optical mode converter system, power transfer efficiency reaches to 85.62%.4. Based on vector diffraction theory and Katsenelenbaum-Semenov algorithm, quasi-optical mode conversion system for 140 GHz, TE28,8 mode including two phase-correcting mirrors has been designed, the power transfer efficiency is 93.33%, vector correlation coefficient is 97.71% and scalar correlation coefficient is 99.11%; The power transfer efficiency of the quasi-optical mode converter system for 94 GHz, TE6,2 mode including one phase-correcting mirror reaches to 88.39%, vector correlation coefficient of 91.32%, scalar correlation coefficient of 94.94%, the power transfer efficiency of the quasi-optical mode converter including two phase-correcting reach to 88.39%, the vector correlation coefficient of 99.23%, the scalar correlation coefficient of 99.43%.5. Using the coupled wave theory to design the Denisov launcher. The length of the Denisov launcher for 140 GHz, TE28,8 mode with the taper reaches to 205.2mm, cut length of 47.2mm. In the Brillouin zone the scalar correlation coefficient greater than 98% and the vector correlation coefficient greater than 85%. The length of the Denisov launcher for 94 GHz, TE6,2 mode with the taper reaches to 49 mm, cut length of 17 mm. Finally simulation software(LOT) proves the correctness of the design.This thesis investigates the quasi-optical mode converter system(launcher and mirror). According to the demand of gyrotron oscillator structure and size, a variety of quasi-optical mode converter system have been designed, especially by using the vector diffraction theory method to design phase corrected mirror for the first time, which is more accurate than the scalar diffraction theory to design phase corrected mirror. At last, the performance of designed Denisov launcher is better than the same type of foreign literature reported.