TMAP7 simulations of deuterium trapping in pre-irradiated tungsten exposed to high-flux plasma

Tungsten targets are irradiated with 12.3 MeV W4+ ions to damage levels up to 2.0 displacements per atom. These irradiated targets are then exposed to high-flux deuterium plasmas with surface temperatures ranging from 360 to 950 K. Nuclear reaction analysis shows significant enhancement of retention in the damaged region of the tungsten for all temperatures. Thermal desorption spectroscopy (TDS) shows an enhancement of both high energy and low-energy trap concentrations due to the W4+ irradiation although the distribution of the trapped deuterium among these different trap types can vary strongly with temperature. In this investigation, TMAP7, a 1-D slab model hydrogen transport code, is used to fit the TDS spectra to gain insight into the trap energies and evolution and trapping mechanisms during the plasma exposure. At lower temperatures the trapping is diffusion-limited, while at the highest temperatures, there is a significant fraction of unfilled low-energy traps and trap annealing. (C) 2011 Elsevier B.V. All rights reserved.