Advanced Design of Quasi-Optical Launchers for Fusion Plasma Heating

60176 Current high power gyrotron tubes, used for heating fusion plasmas, produce power in high order TE modes, which are converted to a Gaussian like mode through use of an internal mode converter and launcher. However, these converter systems typically achieve only 85-90% efficiency for conversion of cavity output power to a usable Gaussian mode, leading to significant efficiency degradation. Current analysis software used to design the mode converter and launcher system are based on approximations that limit solution accuracy, thereby limiting the ability to achieve designs with high efficiency. This project will develop an exact integral formulation of the problem that will allow for the design of high efficiency converter/launchers. In Phase I, an exact magnetic field integral equation analysis computer code, which used the forward-backward method for an iterative solution, was developed. Using this code, calculations for a test launcher had excellent agreement with measurements, demonstrating the feasibility and accuracy of the integral equation approach. In Phase II, an advanced engineering code for the converter/launcher analysis will be developed that uses integral formulation analysis and techniques to minimize the computational load. A high-efficiency mode converter and launcher system for use in a high average power DOE gyrotron will be designed. Commercial Applications and Other Benefits as described by the awardee: Successful development should increase the efficiency of Gaussian mode gyrotrons used for plasma heating in fusion devices. The technique should also be applicable to other overmoded, high-power microwave components such as waveguide converters, power combiners, elbows, and mirrors. These components have applications in research and medical accelerators, materials processing, and high-power millimeter wave radars.