A Beam Waveguide Launcher for High Power ECRH Heating in Large Tandem Mirror Machines

We explore the possibility of applying a quasi-optical beam waveguide of the Cassegrain type as a launching system for RF heating of a fusion plasma. The plane wave required for proper operation of the Cassegrain antenna can be obtained from the azimuthally polarized TE0n gyroton output by means of, e. g., a horn reflector with a stepped-twist reflector mounted in its throat. Our launcher has the potential to keep the loss level extremely low, continue the outputs of a number of gyrotrons, and direct the radiation on the plasma in specific directions and polarization states.