Study of lithium and carbon sputtering from lithium-coated graphite plasma facing components in the NSTX divertor

In this work, the behavior of lithium conditioned graphite PFCs in the NSTX divertor is characterized in terms of lithium and carbon sputtering yields and gross impurity influxes during H-mode ELM-free NBI-heated discharges. Impurity influxes and sputtering yield measurements in the NSTX divertor are derived from photometrically calibrated filtered cameras and divertor Langmuir probes via the S/XB method. Neutral lithium sputtering yield $Y_{Li}$ from solid lithium coatings in NSTX is found to be consistent with values reported from test stand experiments (with $Y_{Li} \sim 0.03-0.07$). Temperature-enhanced sputtering yield is generally observed for surface temperatures above the lithium melting point (with $Y_{Li} \sim 0.1-0.2$) in the proximity of the divertor strike point, leading to divertor gross lithium influxes of a few $10^{21}$ atoms/s. A moderate reduction of the carbon sputtering yield is observed with the application of lithium coatings with gross divertor carbon influxes of several $10^{20}$ atoms/s.