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Beryllium Layer Deposition on Carbon and Tungsten from Beryllium-Seeded Plasmas

The deposition of beryllium (Be) on carbon (C) and tungsten (W) has been studied at the PISCES-B divertor simulator. Samples of C and W were exposed to a deuterium plasma that was seeded with Be from a small effusion cell mounted ˜120 mm upstream from the sample. The incident and eroded flux of Be from these samples was monitored through visible light spectroscopy. The surface composition and layer thickness were measured using Auger electron spectroscopy and ion beam analysis. Results on the formation of Be layers on C and W focusing on the layer growth rate and thickness as functions of temperature are presented. Modeling calculations of Be layer formation on graphite can explain the equilibrium surface composition, but a prediction of the layer formation rate is hampered by an incomplete model of the influence of surface morphology on chemical erosion of the surface. For Be layer formation on W, the modeling calculations including Be diffusion and sublimation correctly predict the Be uptake into the W surface.