Power handling limit of liquid lithium divertor targets

A model is formulated to make a first estimate of the maximum tolerable power of liquid lithium divertor targets, and to gain insight into their behavior in terms of lithium loss rate and surface temperature. The model,formulated as a simple analytical expression, states that the incoming power is balanced by heat conduction through the target and by the lithium which is dissipating energy via evaporation, radiation and ion-neutral friction. A target is considered to fail when the net lithium loss flux from the surface exceeds the available supply. The model is evaluated over a range of input parameters: lithium supply rate, surface layer thickness, redeposition coefficient, and dissipated energy per Li particle lost to the plasma. Based on the results, first, surface temperature locking is expected above a deposited power of 10 MW/m2. Second, lithium targets are expected to be extremely robust against power deposited during short transient events. A surface layer thickness of 50 micron is sufficient to withstand 60 MJ/m2 vertical displacement events or 20 MJ/m2 disruptions.