Evolution of the pedestal on MAST and the implications for ELM power loadings

Studies of the pedestal characteristics and quantities determining edge-localized mode (ELM) energy losses in MAST are presented. High temperature pedestal plasmas have been achieved which have collisionalities (νped* = 0.03-0.1) one order of magnitude lower than previous results (νped* = 1-5). A stability analysis performed on these plasmas shows them to be near the ballooning limit. The fraction of pedestal energy released by an ELM as a function of collisionality on MAST is consistent with data from other devices. The evolution of the filamentary structures observed during ELMs has been studied and has shown that they exist near to the last closed flux surface for the time over which the majority of particles and energy are being released from the pedestal region into the scrape off layer. A simple model has been developed, which is in reasonable agreement with the observed ELM energy losses and target profiles