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(33) m(-2). XPS analysis evidenced the formation of WxNy 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.