New results on carbon release and transport in ASDEX-Upgrade

The behaviour of carbon in the divertor of ASDEX-Upgrade is investigated by means of optical spectroscopy, bolometry and thermography. Apparent chemic al erosion yields, derived from CH molecular band emission and Hp spectrosc opy are shown to exhibit a pronounced flux dependence and isotope effect, Y -chem proportional to m(H) x Gamma(-01.7), while no dependence on surface t emperature (T-surf < 100 degrees C) and impact energy is seen. The flux and isotope dependences also show up in the CII, CIII and total carbon radiati on. The weak correlation between the carbon yields in the divertor and the core plasma carbon concentration supports the assumption that main chamber sources are important for the core plasma carbon content under the low temp erature, high recycling conditions of this study. (C) 1999 Elsevier Science B.V. All rights reserved.