FLUX DEPENDENCE AND ISOTOPE EFFECT OF THE CHEMICAL EROSION OF CARBON UNDER TOKAMAK CONDITIONS

Chemical erosion of carbon is investigated in the outer Divertor II of the ASDEX Upgrade tokamak for ion flux densities up to 1023 m 2 s 1 and up to reactor-relevant values of the power per major plasma radius, P/R 12 MW/m. Surface temperatures are relatively low and do not exceed 100 oC at the position of the measurements. The erosion yields calculated from CH molecular line emission exhibit a pronounced hydrogen flux dependence and an isotope effect, resulting in lower yields for higher fluxes and a factor of 2 higher yields for deuterium in comparison to hydrogen. Corresponding yields derived from carbon ion lines corroborate these results. The observed parameter dependences of the chemical erosion yields can be described with the analytical model of Roth and Garcia-Rosales, Nucl. Fusion 36 (1996), if an additional, empirical time constant for the hydrogenation process is introduced.