3D modeling of the ASDEX Upgrade edge plasma exposed to a localized tungsten source by means of EMC3-Eirene

We report on simulations carried out by the Edge Monte Carlo 3D (EMC3)-Eirene code package of ASDEX Upgrade divertor discharges exposed to a localized source of W impurities and compare our results to dedicated experiments. By injecting the impurities first into the divertor and then into the main chamber while observing the impact on the impurity concentration in the core we can determine the 'divertor retention' R, i.e. the capability of the divertor to screen the core from impurities. The simulations show a strong dependence on the strike point-source distance and on collisionality. Experiments with a massive introduction of W with a melting W pin in the divertor and a moderate injection of W in the main chamber yield a value of R similar to 25 which seems to be consistent with the simulation. (C) 2010 Elsevier B.V. All rights reserved.