Kinematic and thermodynamic effects on liquid lithium sputtering

Lithium sputtering yields of D+, H+, He + and Li+ on D-saturated liquid lithium and liquid tin-lithium at 45-degree incidence have been measured and modeled in the energy range of 100–1000 eV. These sputtering yields are also measured as a function of target temperature ranging from 200–420°C. In addition the secondary sputtered ion fraction under various conditions are measured as well. The Ion-surface InterAction Experiment (IIAX) is designed to measure the lithium-sputtering yield in liquid phase from bombardment with a Colutron Ion source. The lithium sample is treated with a deuterium plasma from a hollow cathode source. Measurements also include bombardment of non D-treated lithium surfaces.; Results suggest that preferential sputtering of deuterium atoms over lithium atoms in D-treated samples significantly decrease the absolute sputtering yield of lithium by at least 60% in the case of He+ bombardment. The secondary sputtered ion fraction for lithium bombardment has been measured for a variety of incident particle energies and sample temperatures. The fractions measured vary from 55–70%. Liquid lithium sputtering at or just above the melting point shows little difference between solid and liquid phase sputtering. As the temperature is raised a non-linear enhancement is noted in the lithium-sputtering yield from various bombardment conditions for both liquid lithium and liquid tin-lithium. The enhancement measured in IIAX is caused by a combination of temperature-dependent effects. In addition, the evaporation flux measured in IIAX indicates coverage by segregated oxygen from the sample bulk. Other results include lithium-sputtering results under high-flux conditions (i.e. tokamak exposures) are consistent with lithium sputtering results in IIAX for solid lithium and temperatures near or at the melting temperature. All experimental results are complemented with Monte Carlo simulations using VFTRIM-3D, where a fractal dimension equal to 2.00, consistent with a flat surface, is used for the liquid phase cases. In addition to simulations analytical and semi-empirical models have been developed to help explain lithium-sputtering reductions by deuterium treatment and lithium-sputtering enhancement by possible thermal or displacement spike effects, among other mechanisms.