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

The Lithium Evaporation EXperiment (LEEX) campaign on the Hybrid Illinois Device for Research and Applications (HIDRA) investigates helium retention effects induced by in-operando lithium evaporations into HIDRA. Lithium droplets were applied to tungsten samples and then exposed to a 600 s helium plasma at different distances, D, from the plasma edge. LEEX data has confirmed previous results at the University of Illinois Urbana-Champaign of in-operando lithium evaporations producing a low recycling regime for HIDRA helium plasmas and additionally proves the retained species is helium. The lithium evaporation from the D = 25 mm 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 aims to investigate this. This study’s outcomes are thoroughly presented and provides additional justification for conducting further research on lithium’s behavior in fusion environments, given its substantial potential impact on the development of PFCs.