Vapor shielding of liquid lithium divertor target during steady state and transient events

摘要

We develop a OD model of vapor shielding including a vast variety of processes in the vapor cloud and plasma-surface interactions. The model is applied to a liquid lithium (Li) divertor with targets covered by a self-restoring Li coating. Calculations show that in the steady state, the target heat flux saturates with increasing external heat flux at approximately 7.5 MW m~(-2). This value may seem very optimistic. However, we show that a significant part of the external heat is removed with the eroded particles. Hence, the maximum sustainable heat load is restricted by the coating renewal rate. The response of the coating to pulsed loads similar to the ITER-scale type I edge localized modes (ELMs) demonstrates high shielding efficiency. Similar to the steady-state regime, the coating renewal rate is the critical quantity for the target survival under pulsed heat loads. Surviving an ELM with an external heat load of 100 MW m~(-2) requires a fast coating recovery rate (10~(26) m~~(-2) s~(-1)) or a substantial reservoir of Li on the surface, which may be a concern for some target designs.