The measurement of electron density and poloidal magnetic field in a Tokamak by polarization changes in an EM wave

Abstract

Describes the theoretical basis of a method of measuring the radial distribution of electron density and poloidal magnetic field in a Tokamak from the polarization changes occurring in a test wave propagating across a series of chords of the discharge. When the test wave is linearly polarized at an angle of 45 degrees to the toroidal direction the power transferred to a direction perpendicular to the initial polarization is related to electron density only. When the initial polarization is directed along the toroidal direction the power transferred to the perpendicular direction is related to both electron density and poloidal field. The optimum wavelength to obtain maximum power transfer to the direction perpendicular to the initial polarization is lambda approximately 1 mm. An experimental multi-channel system using a far infrared laser source is suggested.