Reduction of the Ohmic Loss of Miter Bend Polarizer Mirrors for High-Power Long-Pulse ECRH Systems

A set of two corrugated polarizer mirrors is typically used in high-power Electron Cyclotron Resonance Heating (ECRH) systems to provide the required polarization of the ECRH output beam. The ohmic losses of these mirrors can significantly exceed the losses of plane mirrors depending on the polarization of the incident beam with respect to the orientation of the grooves. Since polarizer mirrors incorporated into miter bends of a corrugated waveguide line are limited in size, active water cooling can become critical in high-power cw systems like the one for ITER. The ohmic loss of polarizer mirrors has been investigated experimentally at high power using different mirror materials. A strategy to minimize the losses for given mirror geometries has been found. Results for different groove geometries are compared.