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P: Fachverband Plasmaphysik
P 11: Poster Session- Plasma Wall Interaction
P 11.1: Poster
Dienstag, 1. März 2016, 16:30–19:00, Empore Lichthof
Study of the Temperature Dependent Nitrogen Retention in Tungsten Surfaces by XPS-Analysis — •Ulrike Plank1,2, Gerd Meisl1, and Till Höschen1 — 1Max-Planck-Institut für Plasmaphysik, Boltzmannstr. 2, D-85748 Garching — 2Fakultät für Physik der Ludwig-Maximilians-Universität München, Schellingstraße 4, D-80799 München
To reduce the power load on the divertor of fusion experiments, nitrogen (N) is puffed into the plasma. As a side effect, nitrogen gets implanted into the tungsten (W) walls of the reactor and forms nitride layers. Their formation and, therefore, the N accumulation in W showed an unexpected temperature dependence in previous experiments. To study the nitrogen retention, we implanted N ions with an energy of 300 eV into W and observed the evolution of the surface composition by X-ray photoelectron spectroscopy (XPS). We find that the N content does not change when the sample is annealed up to 800 K after implantation at lower temperatures. In contrast, the N concentration decreases with increasing implantation temperature. At 800 K implantation temperature, the N saturation level is about 5 times lower compared to 300 K implantation. A possible explanation for this difference is an enhanced diffusion during ion bombardment due to changes in the structure or in the chemical state of the tungsten nitride system. Ongoing tungsten nitride erosion experiments shall help to clarify whether the strong temperature dependence is the result of enhanced diffusion or of phase changes.