Theoretical study of hydrogen desorption from tungsten in divertor conditions*

Using a recently developed W-H interatomic potential [1], H thermal desorption from W surface is simulated for various material temperature T=1000K-1700K and low H surface coverage. It is observed that both atomic and molecular H desorption occurs at similar rates, and are of second order with respect to H surface coverage. Both desorption processes follow a H precursor state [2] induced by H-H short-range interactions on W surface. The second order nature of atomic desorption results from such precursor state.

H desorption induced by incoming H ions may be comparable to thermal desorption when W surface  is saturated with H. Ion-induced H desorption is characterized by simulating H particles impinging onto a fully covered W surface. At low incident energy <1eV, impinging H either deposit onto W surface, or induce molecular desorption. In contrast, impinging H at higher incident energy ~10eV induce atomic desorption of one or two separate H atoms. [1] Wang, Journal of Physics: Condensed Matter (2017) [2] Cassuto, A. Surface Science (1981)