Determination of the Poloidal Magnetic Field Profiles in a Tokamak by Polarization Spectroscopy of an Impurity Ion Line

Abstract

Profiles of the poloidal magnetic field in Ohmically heated, sawtoothing discharges are determined in the Texas Experimental Tokamak (TEXT) from a precise measurement of the partial circular polarization of an impurity-ion line, TiXVII 3834 \AA{}. The sawtooth-period-averaged safety factor (inverse of the rotational transform) on the plasma axis is found to be close to 1.0, independent of its value on the plasma edge. The measurements indicate a decoupling of the current and temperature profiles and a flat current density profile in the center of the discharge.