Modeling Impurity Transport in the HIDRA Stellarator During In-Operando Lithium Evaporation*

Interest in the use of lithium as a plasma facing component (PFC) has increased over the years due to lithium’s low-Z nature and the self-healing characteristics of flowing liquid metal divertors. Recent experimental campaigns on HIDRA as part of the domestic LMPFC program have identified and confirmed an additional benefit: Helium retention behavior during in-operando evaporation of lithium into a helium plasma. Post-experimental observations revealed patterns characterized by ‘double streaks’ of lithium deposition on the vacuum-vessel wall.  In this study, we compare these experimental observations with simulated ion transport in the scrape-off layer on a full 3D mesh of HIDRA’s magnetic field. The magnetic field is solved through direct application of the Biot-Savart law and corroborated against previous measurements and studies on HIDRA, while particle motion is modeled via the Boris-Buneman algorithm and parallelized over multiple CPU cores. Results of our simulation display the same ‘double streak’ patterns as observed on HIDRA.