Development of an absorbing first-wall interface: Deuterium trapping in Tantalum cold-spray coatings

Effective control of hydrogen isotopes’ (HIs) partial pressure in the plasma edge in small fusion devices such as WHAM [1] is important to limit energy losses associated with the charge exchange events. We have investigated tantalum (Ta) cold-sprayed deposit [2,3] as a potential plasma-facing material capable of trapping significant amounts of HIs and to withstand the high particle loads at surface temperatures up to 1000 K. Ta was cold-sprayed on 316L stainless-steel substrates under five different spray conditions to achieve a range of coating microstructures. Surface and cross-sectional Scanning Electron Microscopy observations were used to evaluate the microstructure of the coatings. X-ray photoelectron spectroscopy confirmed a presence of a few nm-thick Ta₂O₅ oxide layer on the surface. 95 eV/D ion (deuterium) irradiation of the samples performed at the fluence of ~3×10²⁵ D m^-2 at the surface temperature T_surf=523 K revealed the formation of D incorporated Ta-oxide at the surface. Tantalum deutoride (TaD) was observed in the bulk due to the incorporation of D in the Ta lattice, however no TaD, was observed at T_surf=1000 K. Thermodesorption experiments performed on the ion irradiated samples and samples exposed to a D₂ gas flow revealed enhanced D trapping in the cold-sprayed Ta compared to the bulk Ta when heated up to 1000 K.