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Abstract
Plasma facing components (PFCs) play an important role in the performance of fusion research devices. In order to investigate the effects of liquid lithium plasma facing components on plasma performance, the Current Drive Experiment - Upgrade (CDX-U) spherical torus installed a toroidal liquid lithium tray limiter and an electron beam lithium evaporation system.
Measurements of the effective particle confinement time, [special characters omitted], were performed by using transient gas puffing and observing the time dependence of the plasma density with microwave interferometry. A significant drop in [special characters omitted] was observed in the discharges with liquid lithium PFCs, which is consistent with increased particle pump-put. Spectroscopic measurements also support an overall decrease in the particle flux to the plasma. In order to look at the global particle balance in the CDX-U discharges with liquid lithium PFCs, modeling of the plasma discharges with DEGAS2, a neutral particle transport code, has been performed. Utilizing the available spectroscopic data, this modeling allows a calculation of a global recycling coefficient ( R) for both standard discharges and ones with liquid lithium PFCs. The modeling shows a significant reduction in recycling, with R = 0.75 in the liquid lithium case. An analysis of the impact of light reflections on the spectroscopic measurements was also performed.
