Modeling of the first mirror surface composition under ITER relevant particle irradiation

Metal mirrors are widely used for optical diagnostics in ITER. Degradation of the mirror surface due to erosion and impurity deposition leads to deterioration of its reflecting properties. In the paper the transport of impurities in a cylindrical steel duct and surface composition change of a diagnostic molybdenum mirror irradiated simultaneously with D, He and Be atoms is simulated for the outer equatorial port of ITER. Net-deposition of Be and Fe on the mirror surface is found even for small Be fraction in the incident flux. The main reason is the formation of a mixed layer due to the high-energy CX-neutrals. However, using the protective duct with the aspect ratio L/D=10 leads to 14,000 times reduction of Be flux to the mirror compared to Be flux to the first wall; this characteristic factor is sufficiently lower in the cases of L/D=5 and 2.