The influence of the divertor magnetic configuration and of ELM frequency on target heat fluxes in MAST

ELM characteristics in a large spherical tokamak with significant auxiliary heating are explored. Access to H-mode is significantly easier when the plasma magnetic configuration is near to a connected double null. The change in ELM frequency with core density and/or auxiliary heating power is broadly similar to conventional devices of a similar size in the type III regime. Power at the targets during an ELM arrives predominantly at the outboard side, irrespective of ELM frequency. The data are consistent with transport into the scrape-off layer being driven predominantly by diffusive processes in quiescent periods between ELMs, and thus being distributed roughly according to the 4:1 ratio of outboard to inboard separatrix surface areas. In L-mode and during ELMs themselves, however, the transport is augmented by turbulent processes, which are more prominent at the outboard side, where the field is very low and where the magnetic surfaces have bad curvature.