Effects of self-irradiation on deuterium retention and reflectivity of molybdenum, fusion plasma-facing material: Combined experimental and modeling study

Molybdenum is used as plasma-facing material in tokamaks and as material for plasma optical diagnostics mirrors. Harsh conditions of neutron irradiation, exposure to hydrogen isotopes and helium ions, and high operating temperatures result in degradation of the molybdenum surface and ultimately limit their lifetime in a fusion power plant. In the current paper, intake and subsequent thermal release of deuterium from self-irradiated by high energy (1 MeV) ions molybdenum as a function of irradiation dose are investigated. Several characteristic temperature regions where deuterium release takes place are identified and attributed to trapping of deuterium in intrinsic and radiation-induced microstructure defects. This attribution is further validated by molecular dynamics modeling, which confirms that increase and saturation of vacancy concentration found in simulations follows increase and saturation of experimentally determined deuterium content. Deuterium inventory and vacancy content saturate at a damage level of around 0.2 dpa (displacement per atom), similar to recent modeling and experimental studies of iron and tungsten. Reflectivity measurements of irradiated molybdenum show that it is only slightly affected by damage up to 1 dpa.