Carbon erosion and migration in fusion devices

This paper summarizes observations about net carbon erosion and re-deposition in the limiter tokamak TEXTOR, and the divertor tokamaks ASDEX Upgrade and JET. The major carbon source in TEXTOR is the toroidal graphite belt limiter. Eroded carbon is mainly re-deposited on net deposition dominated areas of that limiter, and on areas perpendicular to the magnetic field in the scrape-off layer. In ASDEX Upgrade and JET the major carbon sources are located in the main chamber. Eroded carbon is re-deposited on the divertor tiles in the inner and to a lesser extent outer divertors. Carbon migration to remote areas without direct plasma contact like the JET louvres, or the area below the divertors II and IIb of ASDEX Upgrade, is observed. Soft, hydrogen rich hydrocarbon layers with a deuterium to carbon ratio of 0.7 - 1.4 are formed in these areas. Precursor for this layer formation is sticking of hydrocarbon radicals like CD(3) or C(2)D(x) (x = 1, 3, 5) created by re-erosion of deposited hydrocarbon layers on the divertor tiles.