Simulation of fast flow liquid lithium divertor for next step fusion devices using coupled boundary plasma transport and liquid metal MHD/heat transfer codes

Plasma computations using the SOLPS-ITER code have been coupled with a liquid metal (LM) MHD/heat transfer code to develop a lithium (Li) open-surface divertor design and assess its impact on the scrape-off-layer (SOL) and core plasma performance for a conceptual future fusion device “Fusion Nuclear Science Facility (FNSF)”. The LM MHD/Heat Transfer code computes the LM flow and surface temperature based on the incident heat flux on the LM surface. The goals of the study are: (1) to identify the required gas puffing and impurity seeding levels to maintain acceptable upstream and core conditions, and (2) to identify the acceptable LM operating temperature window to avoid core contamination due to fuel dilution.

Simulation results indicate that neon (Ne) seeding significantly mitigates divertor heat flux but potentially reduces both upstream electron and main ion density due to fuel dilution and core radiation. The combined application of Ne seeding and simultaneous Deuterium (D₂) puffing is identified to be effective in satisfying all FNSF design requirements on upstream electron density (n_esepm ~10²⁰ m^-3) and the peak divertor heat flux (< 10 MW/m²). The comprehensive analysis through the coupling between the boundary code and the LM MHD code identifies the acceptable Li flow parameters, LM surface temperature, and emitted Li fluxes necessary to meet the major design constraints. The emitted Li fluxes exhibit minimal impact on the upstream plasma at surface temperatures up to approximately 525°C, corresponding emitted Li fluxes of up to ~ 10²³atoms/s. Conversely, evaporation predominantly drives the Li loss processes at higher surface temperatures range (>525°C), contaminating both the divertor and upstream plasma via fuel dilatation.