Three-dimensional (3D) simulations of impurity dynamics in the vicinity ofa Tore Supra ergodic divertor neutralizer are presented and compared withspectroscopic observations for a medium density pulse in the high recyclingregime. The numerical tool used for the description of impurity generationand transport is a version of the Monte Carlo code BBQ, while the geometryof the magnetic field lines is calculated by use of the MASTOC code.Substantial quantitative consistency is found between the experimental dataand our simulations based on recent impurity generation and propagationmodels. For the given plasma conditions, physical sputtering induced byimpact from deuterium ions is found to be the dominant mechanism leading tothe carbon contamination of the edge plasma. Chemical sputtering releases acomparable number of carbon impurities from the surface interacting withthe plasma but those particles are rapidly re-deposited or pumped away. Wefind the role of friction of the impurities with the background plasma tobe of crucial importance for the determination of the impurity distributionclose to the neutralizer. We further find that a flow reversal of thebackground plasma takes place at the leading edge of the neutralizer with aflow velocity of a few per cent of the ion sound speed in the region thatis just clear of the edge.
Time-dependent shell model for spreading of impurities locally injected into hot plasmas