Response of NSTX Liquid Lithium divertor to High Heat Loads
Authors: Tyler Abrams, M.A. Jaworski, J. Kallman, R. Kaitaa, E.L. Foley, T.K. Grayd, H. Kugel, F. Levinton, A.G. McLean, and C.H. Skinner
Abstract:
Samples of the NSTX Liquid Lithium Divertor (LLD) with and without an evaporative Li
coating were directly exposed to a neutral beam ex-situ at a power of ~1.5 MW/m2 for 1-3
seconds. Measurements of front face and bulk sample temperature were obtained. Predictions of
temperature evolution were derived from a 1D heat flux model. No macroscopic damage
occurred when the "bare" sample was exposed to the beam but microscopic changes to the
surface were observed. The Li-coated sample developed a lithium hydroxide (LiOH) coating,
which did not change even when the front face temperature exceeded the pure Li melting point.
These results are consistent with the lack of damage to the LLD surface and imply that heating
alone may not expose pure liquid Li if the melting point of surface impurities is not exceeded.
This suggests that flow and heat are needed for future PFCs requiring a liquid Li surface.
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Submitted to: Journal of Nuclear Materials (May 2012 and 20th International Conference on Plasma Surface Interactions 2012 Aachen, Germany May 21-25, 2012.
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