Mathematical modeling and design of a microwave polarizer for DTT ECRH applications

In an Electron Cyclotron Resonance Heating (ECRH) system, to efficiently couple the signal power to the plasma, the signal wave polarization must be accurately matched to the plasma conditions at the plasma boundary. However, the millimeter-wave radiation from the power source (gyrotron) is normally linearly polarized: consequently, some kind of polarization matching is required. This study focuses on the design of a grating polarizer with sinusoidal grooves for the 170 GHz ECRH system, with an application specifically intended for the Divertor Tokamak Test (DTT), currently under construction in Frascati, Italy. To enable the generation of all possible output polarization states, a pair of polarizer mirrors will be employed and integrated into the Quasi-Optical (QO) transmission line connecting the gyrotrons to the Electron Cyclotron (EC) waves launchers. The primary objective of this study is to describe an analytical tool capable of providing detailed insights into the polarization characteristics of the reflected electric field resulting from the interaction between the incident wave and the polarizer. Additionally, the proposed program tool calculates the precise combinations of rotation angles required for the polarizers to achieve the desired output polarization states. The accuracy and reliability of the model's prediction have been validated by comparing them with simulations conducted using commercial electromagnetic software.