New results on carbon release and transport in ASDEX-Upgrade

The behaviour of carbon in the divertor of ASDEX-Upgrade is investigated by means of optical spectroscopy, bolometry and thermography. Apparent chemical erosion yields, derived from CH molecular band emission and H β spectroscopy are shown to exhibit a pronounced flux dependence and isotope effect, Y chem m H x Γ -0.7 , while no dependence on surface temperature (T surf < 100°C) and impact energy is seen. The flux and isotope dependences also show up in the CII, CIII and total carbon radiation. The weak correlation between the carbon yields in the divertor and the core plasma carbon concentration supports the assumption that main chamber sources are important for the core plasma carbon content under the low temperature, high recycling conditions of this study.