Spatial structure of scrape-off-layer filaments near the midplane and X-point regions of Alcator-C-Mod

Movies of edge turbulence at both the outboard midplane and the region outboard of the typical lower X-point location in C-Mod have been obtained using gas-puff-imaging together with fast-framing cameras. Intermittent turbulence structures, typically referred to as blobs or filaments, are observed in both locations. Near the midplane the filaments are roughly circular in cross-section, while in the X-point region they are highly elongated. Filament velocities in this region are ∼3x faster than the radial velocities at the midplane, in a direction roughly outward across the local flux surfaces. The observations are consistent with the picture that the filaments arise in the outboard region and, as a consequence of the rapid parallel diffusion of the potential perturbations, map along field lines. Results from a 3D BOUT turbulence simulation reproduce many of the spatial features observed in the experiment.