Helium transport and exhaust with an ITER-like divertor in ASDEX Upgrade

After modification of the ASDEX Upgrade divertor, i.e., installation of the 'LYRA'-divertor, extensive helium exhaust and transport studies have been performed to investigate two different aspects important for the development of a steady-state fusion device: (1) helium transport in the scrape-off layer (SOL) and divertor with a divertor geometry similar to the one foreseen for ITER, and (2) helium transport in the plasma core with internal transport barriers (ITBs). In ohmic and H-mode discharges larger compression ratios and enrichment factors as competed to divertor I have been found. With the new divertor configuration both quantities depend on the heating power and deteriorate with divertor detachment. In ITB-discharges with an I-I-mode edge, helium exhaust is rather slow - as expected for such low density scenarios - but not hindered by the transport barrier. (C) 2001 Elsevier Science B.V. All rights reserved.