PSI modeling of liquid lithium divertors for the NSTX tokamak

We analyzed plasma surface interaction issues for the planned Module-A static liquid lithium divertor for NSTX using coupled codes/models describing the plasma edge, divertor temperature, and erosion/redeposition, with input data from tokamak and laboratory experiments. A 300 nm lithium pre-shot deposited coating will strongly pump impinging D⁺ ions. This yields a low-recycle SOL plasma with high plasma temperature, T_e ∼ 200-400 eV, low density, N_e ∼ 1-3 × 10¹⁸ m ^-3, and peak heat loads of ∼8-20 MW/m², for 2-4 MW core plasma heating power. This regime has advantages for the NSTX physics mission. Peak surface temperature can be held to an acceptable ≤470 °C with moderate strike point sweeping (10 cm/s) using a carbon (for 2 MW) or Mo/Cu or W/Cu substrate (2-4 MW). Erosion/redeposition analysis shows acceptable coating lifetime for a 2 s pulse and low core plasma contamination by sputtered lithium.