Carbon transport and escape fraction in a high density plasma beam

Hydrocarbon injection experiments on molybdenum targets facing high-density plasmas in Pilot-PSI were simulated with the 3D Monte Carlo impurity transport and PSI code ERO. Impurity transport and calculation of redeposition profiles were decoupled by calculating carbon redistribution matrices with ERO. Redeposition was found to be strongly dependent on the electron density: greater densities result in a much more localized redeposition pattern. The calculated average number of recycling events of hydrocarbon molecules on the surface went up from 1.5 for ne=5×1019m-3 to 19.2 for ne=4×1020m-3; at the latter density, only 2.4% of the hydrocarbon molecules escapes the simulated plasma beam without returning to the target at least once. Agreement with experimental deposition profiles in argon was fair. The results in hydrogen point towards a strong gradient in chemical erosion yield along the target.