Carbon Deposition and Deuterium Inventory in ASDEX Upgrade

Abstract Carbon erosion and deposition in the ASDEX Upgrade divertor was investigated using a poloidal section of marked divertor tiles and silicon samples below the divertor structure. The whole 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). Identified carbon sources in the main chamber are too low by a factor of ten to explain the observed carbon divertor deposition, but carbon erosion is observed at the outer divertor tiles. Deuterium is trapped mainly on the surfaces of the inner divertor tiles. The long term retention in codeposited hydrocarbon layers is about 3 % of the total deuterium fuel input. 1