Studies on Impurity Retainment in the ASDEX Divertor

Abstract The retainment and exhaust capability of the ASDEX divertor for neon and argon is investigated during ohmic heating and neutral injection heating. No pronounced influence of the scrape-off layer on the divertor particle outflux is observed, though ionization of neutrals in the divertor throats is most likely. The divertor outfluxes behave as if they are determined by the molecular flow conductances of the divertor throats. The plasma impurity outfluxes show strong top-bottom asymmetries which reverse with the direction of the toroidal field. The exhaust capability can be demonstrated by comparison with limiter discharges. The exhaust efficiency of the double-null configuration is about twice that of a single-null configuration.