Experiments and simulation of edge turbulence and filaments in MAST

Experimental and simulation results on filamentary structures observed in the Mega-Amp Spherical Tokamak (MAST) are presented and discussed. Fast camera data have been used to determine the mode number, toroidal and radial sizes and velocities of the filaments observed in L-mode, inter-edge localized mode (ELM) periods and ELMs which are summarized. Automated methods are applied to the analysis of L-mode image data in order to measure dependence with plasma parameters. This indicates that the mode number of L-mode edge turbulence increases with density and decreases with q95, while filament width has the opposite dependence. Simulations of L-mode discharges using the 3D, 2-fluid BOUT code produce similar sizes and radial velocities to the observations, and indicate that the source of these filaments is within a region ∼2 cm from the plasma edge in a spontaneously formed E x B shear layer. Ion temperature fluctuations in these filaments are found to be approximately double the magnitude of electron temperature fluctuations, probably due to fast parallel electron heat transport.