Effects of Lithium Plasma-Facing Surfaces on Particle Confinement in CDX-U

Recent experiments on the CDX-U spherical torus have successfully achieved a significant reduction in recycling with large-area liquid lithium plasma-facing surfaces. The effects of a liquid lithium toroidal limiter and evaporative lithium coatings on overall density and $\tau_p^*$ will be presented. Such conditions have also demonstrated the need to improve plasma fueling. To address this challenge, a supersonic gas injector, based on a Mach 8 Laval nozzle design,[1] has been installed on CDX-U. The fueling efficiency of the nozzle compared to standard gas puffing will be compared. [1] M. Baumgartner, Ph. D. thesis, Princeton University (1997)