Ammonia formation and W coatings interaction with deuterium/nitrogen plasmas in the linear device GyM

In this work results of the first D 2 /N 2 experiments in GyM, a linear device able to produce plasmas of interest for the ITER divertor ( n e 5 ⋅ 10 10 cm −3 , Te 5 eV, ion flux 3–5 ⋅ 10 20 m −2 s −1 ) are presented. Plasmas simulating a N-seeding scenario have been performed to evaluate ammonia formation and its effect on exposed W coatings. The presence of ND emission lines in the plasma can be correlated with the formation of ammonia, further directly detected and quantified by chromatography analysis of the exhaust. Four different W specimens were exposed in GyM to a plasma fluence of 8.78 ⋅ 10 23 m −2 . XPS analysis evidenced the formation of W x N y layers with nitrogen concentration in the range of 1–10% depending on the initial morphology and structure of the W samples. In all analyzed cases, nitrogen was bound and retained within the first 6 nm below the surface and no further diffusion of N into the bulk was observed.