Current density profile measurement on the Texas Experimental Tokamak using a heavy ion beam probe

For the first time, a heavy ion beam probe has been used to measure the poloidal magnetic flux in a tokamak. In this measurement, first proposed over 20 years ago, the toroidal displacement of the heavy ion beam probe particles is caused by the force of the poloidal magnetic field on the ion beam probe particles. In a nearly toroidally symmetric device such as the Texas Experimental Tokamak, the toroidal position of the ions at the detector consists of a part proportional to the poloidal magnetic flux at the sample volume and an integrated contribution of the poloidal magnetic flux along the trajectory. The local part in the relation between beam position and magnetic flux is used as a correction term in an iterative algorithm that calculates the poloidal magnetic flux. The q profile and the current density profile can be derived from the measured poloidal flux. Errors of the measurement can be due to uncertainties in the analyzer position and also in the knowledge of the location of the sample volume. Al...