Simulations of transport mechanisms across the X-points in snowflake divertors

The snowflake divertor (SFD) has been proposed as a potential solution to the exhaust problem in tokamaks. It is formed by bringing a second X-point into the vicinity of the first, resulting in four divertor legs instead of two. SFD experiments have provided evidence of enhanced transport across the region close to the X-points, resulting in redistributed exhaust power across divertor legs and reduced peak heat fluxes at the targets. A leading candidate for this transport is the churning mode (CM): near the X-points, the SFD features a large region (~0.1 m) with poloidal beta >> 1, which can lead to convection in the poloidal plane. Simulations of the CM have been carried out using a 2D reduced-MHD model in conditions relevant to MAST-U, demonstrating this convection can lead to enhanced transport across the X-points when the ratio of thermal pressure at the X-points to the magnetic pressure at the midplane is greater than around 6%. A simple diffusive model of this transport captures its magnitude, but not its direction amongst the divertor legs. A second candidate for this transport is strong ExB flows driven by parallel gradients. We will present progress towards simulations of this effect with the edge transport code UEDGE, which includes electromagnetic drifts. Early results indicate the effect of these particle drifts may be small in MAST-U conditions.