Particle Confinement Times for Discharges with Lithium Plasma-facing Surfaces 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. Modeling of low recycling discharges with DEGAS2, a neutral particle transport code, has been performed. Utilizing available spectroscopic data, this modeling allows a calculation of a global particle confinement time ($\tau_p$) for the low recycling discharges. The $\tau_p$ values deduced with the modeling were used with $\tau_p^*$ to obtain the recycling coefficient $R$. Measurements of $\tau_p^*$ were performed by using transient gas puffing and observing the time dependence of the plasma density with microwave interferometry. The effects of a liquid lithium toroidal limiter and evaporative lithium coatings on the recycling coefficient $R$ will be presented.