Metal impurity release in diverted tokamak discharges

Plasma materials interaction at the wall of the main plasma chamber of the divertor tokamak ASDEX was investigated by a combined probe, allowing simultaneous measurements of the erosion rate by neutral particles, and the flux and average energy of neutrals. The erosion was measured by collecting part of the released material on a carbon strip. Subsequent surface analysis was performed by electron induced x-ray analysis. Flux and energy of the impinging neutral particles were measured after each single discharge with an energy resolving carbon resistance probe. Such combined measurements yield the erosion yield being characteristic for the erosion process. Data for ohmic discharges in deuterium and helium are compared. It turns out that the carbon resistance probe is a simple but powerful means to study the metal impurity release from the tokamak walls by charge exchange neutrals