Deuterium flux measurements in the edge plasmas of PLT and PDX during auxiliary heating experiments

Abstract

The flux of deuterium in the plasma edge several centimeters outside the limiter has been measured using collector probes during neutral beam heating experiments on the PDX tokamak and rf heating experiments on the PLT tokamak. The dependence of the flux on the distance from the plasma was determined, and the time dependence of the flux was measured with a time resolution of 90 ms. In PDX the deuterium flux decreases rapidly with increasing distance from the plasma. The deuterium flux increased strongly when the beams came on and decreased when they turned off. The depth distribution of the deuterium in the samples, measured using SIMS, shows that when the beams are on, about 30% of the deuterium incident on the probe is superthermal deuterium from the beams. In PLT the deuterium flux decreased only slightly with increasing distance from the plasma. The ICRH heating in PLT caused an increase of about 30% in the flux of deuterium to the samples and in the plasma density. In both machines the deuterium fluxes were fairly low (≲1016 D/cm2s) at the positions sampled.