Possible accuracy of the Cotton-Mouton polarimetry in a sheared toroidal plasma

The Cotton-Mouton effect in the sheared plasma with helical magnetic lines is studied, using the equation for the complex amplitude ratio (CAR). A simple model for helical magnetic lines in plasma of toroidal configuration is suggested. Equation for CAR is solved perturbatively, treating the shear angle variations as a small perturbation, caused by the spiral form of the magnetic lines. It is shown that the uncertainty of the polarization measurements in the toroidal plasma with a spiral form of the magnetic lines does not exceed 1.0–2.0%, which determines the limiting accuracy of the Cotton-Mouton polarimetry. It is furthermore pointed out that the method of a priori subtraction of the “sheared” term may significantly improve the accuracy of the Cotton-Mouton polarimetry.