In-operando Lithium Evaporation Inducing Helium Retention in Long-Pulse HIDRA Helium Plasmas

The Lithium Evaporation EXperiment (LEEX) investigated helium retention effects induced by in-operando lithium evaporations into the Hybrid Illinois Device for Research and Applications (HIDRA) at the University of Illinois Urbana-Champaign (UIUC). Lithium droplets were applied to tungsten samples and then exposed to a 600s helium plasma at different distances from the plasma edge (D=0mm, D=25mm, D=47.5mm). Spectrometers, residual gas analyzers (RGAs), and pressure gauges were employed to characterize the plasma throughout the plasma discharge. LEEX data has confirmed previous results at UIUC of in-operando lithium evaporations producing a low-recycling regime for HIDRA helium plasmas and additionally proves the retained specie is helium. The lithium evaporation from the D=25mm case had an 85.3% ± 1% increase in helium retention in the low recycling regime when compared to the steady state plasma of the LEEX control shot. Data presented substantiates previous helium retention claims and advances research surrounding liquid metal PFCs. A retention mechanism has not been identified, but further research utilizing HIDRA and HIDRA-MAT aims to investigate this. This study's outcomes are thoroughly presented and provide an additional justification for conducting further research on lithium's behavior in fusion environments, given its substantial potential impact on the development of plasma-facing components (PFCs).