Speaker
Description
Liquid metal (LM) divertor conditions for a pilot-plant class tokamak are simulated using a multi-component integrated model which considers plasma transport, LM magnetohydrodynamics and heat transfer, and formation and transport of lithium released from the divertor surface. Fast-flow LM divertors have several intrinsic advantages over solid surface concepts due to their self-replenishing nature and low atomic charge, avoiding long-term erosion and unacceptable core radiation issues that are faced by tungsten divertors. On the other hand, lithium can still lead to unacceptable core ion dilution and particles emitted via evaporation and sputtering should ideally be confined to the near-SOL to avoid accumulation on first wall components. Limiting these effects leads to maximum liquid lithium and plasma temperatures to keep evaporation and sputtering to tolerable levels. To better understand the lithium sourcing, transport, and impact on the plasma, integrated models are required.
Building on previous open-surface LM divertor modeling using SOLPS-ITER [1,2], a new workflow includes the OpenEdge code [3] for a self-consistent description of sputtering, evaporation, and droplet transport applied. The integrated model is applied to the CAT tokamak [4], modified to have flat target plates consistent with a fast-flow liquid lithium divertor concept. OpenEdge is a multi-purpose Monte Carlo code which traces neutral and charged particles against a prescribed plasma background considering Lorentz forces, plasma collisions, and for this problem mass and size evolution due to evaporation. Several characteristic lithium macroparticle mechanisms are considered, including mist (~um scale), droplets (~mm scale), and ligaments (~cm scale), supported by two-phase flow simulations. Depending on the size and velocity of the macroparticles, time-dependent simulations may be used to describe the effect of the emission on the background plasma state. Initial results of the coupled workflow and an assessment of compatibility the LM divertor concept for CAT will be presented.
[1] M.S. Islam et al 2024 Nucl. Fusion 64 056036
[2] S. Smolentsev S. et al 2022 IEEE Trans. Plasma Sci. 50 4193
[3] A. Diaw et al OpenEdge: A collaborative, multi-purpose direct simulation Monte Carlo for plasma simulation in magnetic fusion environments, submitted to Computer Physics Communications
[4] R.J. Buttery et al 2021 Nucl. Fusion 61 046028