Rapid Vapor-Driven Plasma Contamination and Suppressed Net Lithium Surface Loss in the HIDRA Stellarator

Experiments in the HIDRA stellarator show that the inferred lithium net-loss suppression factor R_eff, which absorbs effects from redeposition, recycling, and slow evaporation, remains between 0.91 and unity across hydrogen and helium plasmas. This implies a lithium lifetime far longer than would be expected from the evaporation rate alone. Lithium surface temperature locking appears only intermittently, and high-temperature operation consistently drives lithium release that overwhelms the available fueling. As a result, the plasma transitions quickly to a lithium-dominated regime, preventing sustained operation in vapor-shielding-relevant conditions. Despite HIDRA’s relatively low densities and particle fluxes, these findings highlight that unmitigated lithium vapor readily contaminates the confined plasma, underscoring the need for active capture or control to achieve stable lithium-based plasma–material interaction regimes.