Electric currents in the scrape-off layer in ASDEX Upgrade

Scrape-off layer (SOL) currents are measured by means of Langmuir probes an d shunts in the divertor of ASDEX Upgrade. They consist of the overlayed co ntributions of thermoelectric and Pfirsch-Schluter (PS) currents. The SOL c urrents exhibit a drastic decrease when the line-averaged density approache s the Greenwald density in the I-I-mode. An analytical model is presented w hich reproduces the measured thermoelectric current quantitatively. Matchin g of the analytical model with the measured current scaling yields informat ion about divertor temperatures and SOL e-folding lengths. (C) 2001 Elsevie r Science B.V. All rights reserved.