Measurement of the Poloidal Magnetic Flux in the Text 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 poloidal magnetic field force. In a nearly toroidally symmetric device such as the Texas Experimental Tokamak (TEXT), the toroidal position of the ions at the detector consists of a part proportional to the poloidal flux in a localized sample volume and an integrated contribution of the poloidal magnetic flux along the ion beam trajectory. Within a single shot, data is taken from several sample volumes. The poloidal magnetic flux at each sample volume is obtained with an iterative algorithm whose corrections are based on the local term. The q-profile and the current density profile can be derived from the measured poloidal flux. Measurement errors can be caused by uncertainties in the analyzer position, the sample volume location, the plasma current, and the plasma position. It is also essential to know the magnetic field outside the plasma. The calculation of the outside field is complicated by the presence of the iron core. The cumulative effect of these uncertainties is a 1% error in the poloidal flux measurement. The current profiles and q-profiles were measured for discharges with on-axis and off-axis electron cyclotron resonance heating (ECRH) and with impurity injection. The current profiles for central ECRH discharges are peaked, as are the profiles for impurity injection. The current profiles for off-axis ECRH discharges are broadened.