Influence of Nitrogen on Deuterium Retention in Polycrystalline Tungsten under Sequential and Simultaneous Irradiation

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 observed effect of the N-containing layer on the temperature dependence of deuterium retention during TDS suggests that the stoichiometry of the W:N layers produced are different at different temperatures. It is found that SIM irradiation resulted in a small overall increase 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.M.A.S