Model development and analysis of temperature-dependent lithium sputtering and sputtered Li+ transport for tokamak plasma-facing applications

We developed and applied models for overall (atom + ion) sputtering and sputtered Li+ transport of liquid lithium tokamak divertor surfaces. The model/analysis has four parts: (1) a temperature-dependent data-calibrated empirical/code (TRIM) model of lithium sputtering by D+ and Li+ as a function of incident particle energy and angle; (2) temperature and energy-dependent molecular dynamics (MolDyn) modeling using an effective interionic pair potential of surface-reflected redeposited Li+; (3) analytical model of reflected lithium charge state; and (4) analytic model of Li+ near-surface emission/redeposition cascade. We predict: (1) strong temperature dependence of sputter yields, (2) reflection coefficients of order 50% (thermal energies) and 10% (hyperthermal energies), (3) reflected lithium charge fractions of 10–30% near 1 eV incidence, and (4) enhanced but non-runaway Li emission for the studied surface temperature range between 473 and 653 K.