Cotton-Mouton Effect Measurement in a Plasma at the W7-AS Stellarator

A Cotton-Mouton effect polarimeter operating in the submillimeter wave region has been developed at the W7-AS stellarator. The transmission matrix representative for the change of polarization state of a probing wave has been calculated and significant elements are determined experimentally. Systematic magnetic field scans over a wide range of the magnetic field conducted at two different probing frequencies were carried out for the first time. These scans clearly demonstrate that the Cotton-Mouton effect is being observed under optimal experimental conditions. The experimental setup measures the line integrated electron density unambiguously and has proven its robustness under various conditions.