Erosion of plasma facing components by arcing at ASDEX Upgrade

摘要

The plasma facing components (PFCs) in a future fusion device has to meet several requirements. A low yield for physical and chemical erosion will allow long live time and reduces the contamination of the plasma. A high melting temperature and high heat conductivity is needed to withstand the power input from the plasma. Additionally manufacturing and costs issues have to be taken into account. In this contribution the possible contribution of arcs, which are observed in all major tokamak experiments, on the erosion of PFCs is discussed. Commonly the material released by arcing is assumed to be insignificant in comparison to physical sputtering and chemical erosion. Recent investigations with metallic PFCs at the inner divertor baffle region of ASDEX Upgrade (AUG) show that locally arcing can be the dominant erosion meachanism[l]. Differently to the sputter process, a significant amount of material is released during arcing as droplets, i.e. spheres of a typical size of some microns. For tungsten it was found that a significant fraction of the dust collected in AUG consists out of these droplets [2]. In the literature erosion by arcs is mostly investigated without or with magnetic fields perpendicular to the surface. In fusion devices the magnetic field lines hit the PFCs under a shallow angle. This may influence the release of molten material, i.e. the production of droplets.