Deuterium retention in NSTX with lithium conditioning*

Fuel retention is an important constraint in the selection of plasma facing materials for next-step tokamaks. Gas balance measurements of retention in NSTX have been performed before- and with lithiumization of the vessel. The gas retained in ohmic discharges was measured by comparing the vessel pressure rise after a discharge to that of a gas-only pulse with the pumping valves closed. For neutral beam heated discharges the gas input and gas pumped by the NB cryopanels was tracked. Preliminary results show high ($\sim$ 90\%) prompt retention both with- and without lithiumization. Outgassing of deuterium follows, initially at a high rate that then slowed over the following 24 hours to become comparable to the baseline vessel presure rate of rise and reduced the retention to the $\sim$ 50\% level. Four material samples were exposed to the plasma and analysed in-vacuo the same evening in order to investigate the fundamental processes governing particle balance with lithium coatings.