Development of the grating mirror for the high power transmission system and its general theory

In the transmission system of the high power Electron Cyclotron Heating (ECH), many mirrors have been installed in the injection antenna section in particular. In some cases, it is difficult to design a normal mirror due to the restriction of the boundary condition. A grating mirror is one of the solutions in such cases. Moreover, controlled power splitting or combining at high power can be realized by a grating mirror. Diffraction angle, efficiency, and distortion/conversion of the polarization can be controlled by the grating shape design. In this study, we developed a grating mirror to efficiently separate the second harmonics component from the fundamental high power beam at 82.7 GHz and higher harmonics. The performance of this grating is confirmed experimentally for the use of vortex beam formation. During this development, the design procedure of a grating mirror is established and generalized to apply for various purposes. (author)