Calculated Refraction and Cotton-Mouton Effect for a Millimeter-wave Interferometer/Polarimeter on the Compact Toroidal Hybrid (CTH) Experiment

A combined mm-wave interferometer/polarimeter based on the method of Dodel and Kunz$^{1}$ is being developed to measure the density and current profiles of current-driven discharges in the CTH torsatron (R = 0.75 m, a $\sim $ 0.2 m, B $\le $ 0.7 T, n$_{e} \quad \le $ 10$^{19}$ m$^{-3})$. Measurement of the internal magnetic field by Faraday rotation wavelengths is less costly than FIR approaches, but is more susceptible to refraction effects and the Cotton-Mouton (C-M) broadening of the polarization. Computational modeling of Faraday rotation, beam refraction, and C-M effects for wavelengths between 1.0 and 4.0 mm have been performed in 3-D geometry using plasma parameter values relevant to CTH plasmas in order to minimize the undesired refraction and C-M broadening while maintaining an adequate magnitude of Faraday rotation. Study results indicate that a 1 mm system is optimal for the CTH. 1. G. Dodel and W. Kunz, Infrared Phys. \textbf{18}, 773 (1978)