Carbon erosion and deposition on the ASDEX Upgrade divertor tiles

Carbon deposition and erosion were measured on ASDEX Upgrade divertor tiles and below the roof baffle during the operation period 2002/2003. The inner divertor is a net carbon deposition area, while a large fraction of the outer divertor is erosion dominated and the roof baffle tiles show a complicated distribution of erosion and deposition areas. In total, 43.7 g B + C were redeposited, of which 88% were deposited on tiles and 9% in remote areas (below roof baffle, on vessel wall structures). 0.6 g C was pumped out as volatile hydrocarbon molecules. Carbon sources in the main chamber are too low by a factor of more than ten to explain the observed carbon divertor deposition. Carbon erosion is observed at the outer divertor strike point tiles, but it is arguable if material can be transported from the outer strike point to the inner divertor.