Comparison of scrape-off layer behaviour between DIV-I and DIV-II operations on ASDEX-Upgrade

The divertor geometry on ASDEX-Upgrade has changed from an open to a more c losed configuration. The effects of this change on midplane scrape-off laye r profiles for temperature and density are discussed. Investigations concer ning the accuracy of separatrix positions are described. The relation betwe en neutral gas flux density in the divertor and midplane density is analyse d and scalings are presented. No decrease in the maximum achievable density in the II-mode with the new dosed divertor in comparison to the former ope n one has been found. For comparable discharges the scrape-off layer densit y for the closed divertor has been found to be higher or at least as high a s for the open divertor. (C) 1999 Elsevier Science B.V. All rights reserved .