Plasma Facing Surface Composition During NSTX Li Experiments
Authors: C.H. Skinner, R. Sullenberger, B.E. Koel, M.A. Jaworski and H.W. Kugel
Abstract:
Lithium conditioned plasma facing surfaces have lowered recycling and enhanced plasma
performance on many fusion devices. However, the nature of the plasma-lithium surface
interaction has been obscured by the difficulty of in-tokamak surface analysis. We report
laboratory studies of the chemical composition of lithium surfaces exposed to typical residual
gases found in tokamaks. Solid lithium and a molybdenum alloy (TZM) coated with lithium has
been examined using x-ray photoelectron spectroscopy, temperature programmed desorption,
and Auger electron spectroscopy both in ultrahigh vacuum conditions and after exposure to trace
gases. Lithium surfaces near room temperature were oxidized after exposure to 1-2 Langmuirs of
oxygen or water vapor. The oxidation rate by carbon monoxide was four times less. Lithiated
PFC surfaces in tokamaks will be oxidized in about 100 s depending on the tokamak vacuum
conditions.
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Submitted to: Journal of Nuclear Materials (May 2012)
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