Liquid Lithium Divertor Characteristics and Plasma-Material Interactions in NSTX High-Performance Plasmas
Authors: Michael A. Jaworski, et. al.
Abstract:
Liquid metal plasma facing components have been proposed as a means
of solving several problems facing the creation of economically viable fusion power
reactors. To date, few demonstrations exist of this approach in a diverted tokamak and
we here provide an overview of such work on the National Spherical Torus Experiment
(NSTX). The Liquid Lithium Divertor (LLD) was installed and operated for the 2010
run campaign using evaporated coatings as the filling method. The LLD consisted of
a copper-backed structure with a porous molybdenum front-face. Nominal Li filling
levels by the end of the run campaign exceeded the porosity void fraction by 150%.
Despite a nominal liquid level exceeding the capillary structure and peak current
densities into the PFCs exceeding 100 [kA/ m2 ], no macroscopic ejection events were
observed. In addition, no substrate line emission was observed after achieving lithiummelt
temperatures indicating the lithium wicks and provides a protective coating on
the molybdenum porous layer. Impurity emission from the divertor suggests that the
plasma is interacting with oxygen-contaminated lithium whether diverted on the LLD
or not. A database of LLD discharges is analyzed to consider whether there is a
net effect on the discharges over the range of total deposited lithium in the machine.
Examination of H-97L indicates that performance was constant throughout the run,
consistent with the hypothesis that it is the quality of the surface layers of the lithium
that impact performance. The accumulation of impurities suggests a fully-flowing
liquid lithium system to obtain a steady-state PFC on timescales relevant to NSTX.
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Submitted to: Nuclear Fusion (June 2013)
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Download PPPL-4884 (pdf 706 KB 19 pp)
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