Modeling and analysis of mixed-material surface evolution and sputtering

Analysis of near-surface compositional changes in materials exposed to ion fluxes is important to a number of technological applications. These applications include preferential sputtering of multi-component materials, ion implantation, plasma contamination, and erosion of plasma facing components in future tokamak devices such as ITER. A model is developed that addresses the dynamics of compositional changes in the near surface region of a plasma facing component where the synergistic effects of sputtering, implantation, and re-deposition are taken into account self consistently. The Monte Carlo binary collision methodology is combined with phenomenological kinetics modeling to study the evolution of the near surface region and the mixing of incident particles with the target material. To show the model capabilities, example model calculations simulated the evolution of beryllium in the sub-surface region of a tungsten divertor that is exposed to multiple fluxes of deuterium, tritium, oxygen, and beryllium. The calculations show that Be can remain in sub-surface region only if the re-deposition fraction is near 1.0 and the confinement of most implanted Be to that region. The calculations also show that the time needed for Be fraction to reach equilibrium is within 1 s after the start of irradiation.