Evaluating the Impact of Helium Bubble Layers on Hydrogen Diffusion*

We describe a qualitative and quantitative assessment of hydrogen permeation in thin tungsten slabs with a (100) surface morphology using molecular dynamics. The simulations have been performed with and without low-energy 100 eV helium implantation at a flux of 4x10²⁵ He m^-2s^-1 to a fluence of ~4x10¹⁹He m^-2, and have involved either 60 eV H implantation or introduction of a concentrated hydrogen layer at ~10 nm below the surface of the W slab.  The simulations reveal that H diffusion is reduced by the presence of the He nano-bubble layer, and that H is observed to segregate to, and trap at, the interface of the high pressure helium bubbles with the tungsten matrix. These results provide atomistic insight into the mechanisms controlled the reduced permeation and retention of hydrogen during mixed He-H plasma exposure.