Characterization of the 3D Scrape-off Layer and Particle Source with RMP Application at MAST

Using the plasma fluid and kinetic neutral code EMC3-EIRENE, a new 3D scrape-off layer (SOL) was characterized in simulations of H- and L-mode discharges at the Mega-Ampere Spherical Tokmak (MAST) with applied resonant magnetic perturbations (RMPs). Due to these RMPs, there were regions of the previously confined plasma now with field lines of short connection length. By following field lines 100 m from the divertor surfaces, the length of this new extended SOL in the chaotic region, a new volume of the simulation domain was determined where the particle transport is dominated by parallel convection. This open volume was constrained based on a 3-D analysis of the finite fluid flow towards the divertor targets in terms of the local Mach number in the EMC3-EIRENE solution. Due to increased parallel transport, ionizations occurring on these open field lines cannot contribute to the confined plasma density. From this analysis, a fueling efficiency was determined by comparing the fueling within the confined plasma in the axisymmetric cases to the RMP cases where the confined volume was constrained by this physics-based approach to defining the new SOL with direct connection to the divertor. This showed a decrease in the fueling efficiency when RMPs are applied of 21% for H-mode and 12% for L-mode, which is comparable to experimentally determined change.