Comparison of collector probe measurements of sputtered copper fluxes from the ASDEX divertor plate with a two-dimensional computer simulation

Abstract

Cu fluxes in the upper divertor of ASDEX have been measured with a collector probe. Experimental deposition profiles are compared with a two-dimensional computer model based on sputtering of divertor plate Cu by deuterium ions followed by ionisation of the Cu atoms in the divertor plasma and their redeposition onto the plate. Within the experimental uncertainties the profile shapes obtained for standard ohmic discharges were found to be in reasonable agreement. Measured values of Cu deposits were, however, much greater than model predictions. The results indicate that in order to better explain the collector probe measurements, the simple picture of Cu erosion and transport may need to be modified to take into account toroidal plasma asymmetries, sputtering contributions from impurity ions and additional Cu sources. Time resolved measurements on two discharges which were additionally heated by neutral beam injection and lower hybrid wave heating are also presented.