Tungsten erosion by arcs in ASDEX upgrade

The transition from carbon to high-Z divertor devices reduces the erosion of the plasma facing components (PFC) strongly. Arcing as second erosion mechanism beside physical sputtering may now dominating the erosion. A procedure based on photographic techniques, profilometry and scanning electron microscopy was developed to investigate arc damage in ASDEX Upgrade. At the inner divertor baffle region erosion by arcing dominates the physical sputtering by a factor of 7. Whereas the number of arc traces only depends on the position of the tile, the effective erosion strongly depends on the surface resistivity of the PFCs. Video observations with high temporal and spatial resolution correlates the onset of arcing with the appearance of ELMs at the inner divertor baffle.