Characterization of edge instabilities in the Pegasus toroidal experiment

Field-aligned, rotating edge filamentary structures are observed on a routine basis in Pegasus Ohmic discharges. Imaging studies using a fast-framing camera indicate the filaments are large-scale, short-lived, coherent structures with an average lifetime varying between 10 and $\approx$150 $\mu$s. Measurements using a pair of toroidally separated, radially scannable internal magnetic probes indicate that these structures are electromagnetic in nature. They are clearly distinguished from typical $2/1$ tearing activity and appear as low amplitude, broadband ($\leq$150 kHz) magnetic turbulence. These fluctuations are not observed on probes far from the plasma edge, suggesting high poloidal mode number. The high edge current density ($j_{a}\sim100\ mbox{kA/m}^{2}$) and low toroidal field ($|B_{\phi,a}|\sim$ 0.1 T) typical in Pegasus may make the edge unstable to peeling modes. Additional magnetic probe arrays will be implemented, allowing a more accurate determination of $n$ and $m$, as well as estimates of filament propagation velocity.