Effect of hydrogen retention on tungsten erosion by oxygen

One important problem for future tokamak reactors with a tungsten divertor armor is chemical erosion. Impurities such as oxygen contained in the scrape-off layer (SOL) hydrogen isotope plasma at the divertor surface heated by the plasma can form volatile molecular complexes, e.g. WxOy, causing erosion. Interstitial H atoms retained in the implantation layer also participate in the surface processes, creating volatile HxOy complexes, which reduce the formation of WxOy and could mitigate the corrosion effect (H is tritium or deuterium). To consistently estimate the armor erosion by oxygen, the retention of H atoms in the implantation layer and the surface reactions are preliminary modeled. The behavior of H atoms is described by equations that include the diffusion in- and the slowing down by the lattice, and the elastic collisions between hot plasma H atoms and the cold H atoms. Creation, destruction, and sublimation of WO2, WO3, HO, and H2O molecules at the W surface are described in terms of a simplified approach. The possible reduction of the chemical erosion due to the retained hydrogen isotopes is discussed.