Comparison of impurity generation and penetration models with spectroscopyfor the Tore Supra ergodic divertor

Three-dimensional (3D) simulations of impurity dynamics in the vicinity of a Tore Supra ergodic divertor neutralizer are presented and compared with s pectroscopic observations for a medium density pulse in the high recycling regime. The numerical tool used for the description of impurity generation and transport is a version of the Monte Carlo code BBQ, while the geometry of the magnetic field lines is calculated by use of the MASTOC code. Substa ntial quantitative consistency is found between the experimental data and o ur simulations based on recent impurity generation and propagation models. For the given plasma conditions, physical sputtering induced by impact from deuterium ions is found to be the dominant mechanism leading to the carbon contamination of the edge plasma. Chemical sputtering releases a comparabl e number of carbon impurities from the surface interacting with the plasma but those particles are rapidly re-deposited or pumped away. We find the ro le of friction of the impurities with the background plasma to be of crucia l importance for the determination of the impurity distribution close to th e neutralizer. We further find that a flow reversal of the background plasm a takes place at the leading edge of the neutralizer with a flow velocity o f a few per cent of the ion sound speed in the region that is just clear of the edge.