Influence of nitrogen on deuterium retention in tungsten under sequential and simultaneous irradiation

Abstract

Nitrogen is a candidate for impurity seeding to reduce the edge plasma temperature for ITER’s tungsten divertor. Radiation characteristics and plasma performance are improved with N compared to other candidates neon and argon, however questions remain in terms of how the introduction of N might impact deuterium retention in W. The current study compares the influence of N on D retention in W with sequential (SEQ) and simultaneous (SIM) irradiation of D-3%N at 300–700 K with energies 500 eV/D+ and 1000 eV/N+. Thermal desorption spectroscopy (TDS) is used to measure the D retained, and X-ray photoelectron spectroscopy (XPS) is used to investigate nitride formation at different implantation temperatures. The XPS results show that for the beam composition of this study, the removal of N by D is the dominant interaction, working against N retention in W. Differences found between the N layer with D/N co-bombardment vs. N pre-irradiation might be worth considering when extrapolating sequential experiments to reactor conditions. The observed effect of the N-containing layer on the temperature dependence of deuterium release during TDS supports the XPS findings, suggesting that the phases of the W:N layer produced are different at different temperatures. It is found that SIM irradiation resulted in an overall increase (up to a factor of ∼4) in total D retention compared to SEQ and D-only experiments above 500 K. At 300–500 K, the D retention was not significantly changed by nitrogen pre-, post- or simultaneous irradiation.