B2-Eirene modelling of the density limit on ASDEX-Upgrade

The B2-Eirene code package was used to investigate the density limit in ASDEX-Upgrade, both in the old, open divertor configuration and the new, more closed configuration. A combination of time-dependent (directly simulating the experimental scenario of raising the plasma density with an external gas puff) and time-independent runs for discrete densities were performed, with carbon produced self-consistently via physical and chemical sputtering. In addition some time-independent calculations were done without impurities to further elucidate the physics. Good agreement was found with the experiment. In addition the role of flow reversal in the carbon contamination of the main plasma arising from divertor generated sources was clarified. (C) 1999 Elsevier Science B.V. All rights reserved.