Kinetic modeling of lithium impurity transport in the HIDRA stellarator during controlled lithium evaporation
Steven Gula, Nina Mihajlov, Giovanni Diaz, Arnav Goyal, R Maingi, D Andruczyk, Davide Curreli
Post-operational imaging of the Hybrid Illinois Device for Research and Applications (HIDRA) stellarator following controlled lithium evaporation reveals distinct streak patterns of lithium deposition along the vacuum vessel wall. These localized structures exhibit strong alignment with magnetic field topology, suggesting that impurity transport in the scrape-off layer (SOL) is governed primarily by the three-dimensional magnetic geometry and associated electrostatic fields. In this work, large-scale kinetic simulations of trace lithium impurity transport are used to investigate the formation of these deposition structures. The magnetic field topology is reconstructed using a Biot-Savart law approach, from which a normalized flux-surface parameter is computed and used to prescribe the background helium plasma profiles. Electron density and plasma potential are modeled as normalized flux-surface-dependent fields scaled by representative scalar measurements and analytical sheath-based estimates, with the electric field obtained from ∇V p . These reconstructed fields are used to compute lithium ion trajectories and generate spatial maps of deposition on the vessel wall. The simulations reproduce streak-like deposition features aligned with magnetic flux tubes intersecting the wall, and the simulated deposition locations and orientations show qualitative agreement with experimental observations. These results demonstrate that magnetic field structure plays a dominant role in shaping impurity transport and deposition in HIDRA and establish a predictive framework for modeling impurity transport and surface deposition in plasma-surface interaction experiments involving liquid-metal plasma-facing components.
