H-mode Characterization and Edge Stability at Near-Unity Aspect Ratio in \textsc{Pegasus} Discharges*

Unique features of operating at near-unity aspect ratio include: ready access to Ohmic H-mode; operation in the low collisionality regime with strong neoclassical effects; and ELM instabilities driven by peeling and peeling- ballooning modes. Ohmic H-mode is achieved in both limited and diverted configurations by using high-field-side fueling. The access to and characteristics of H-mode regimes as well as various ELM types in \textsc{Pegasus} is currently being explored. Characteristics of the L-H transition are: formation of an edge current pedestal; reversal of the direction of toroidal flow at the transition; doubling of the stored energy; and the presence of ELMs. Modest temperatures and pulse lengths in \textsc{Pegasus} allow the use of insertable probes to measure the properties of the edge plasma with high spatial and temporal resolution, even in ELMy H-mode. A current pedestal in the edge $J(R,t)$ profile is observed in H-mode but not in L-mode operation. This pedestal is destroyed during an ELM event cycle, but returns quickly after the ELM. Peeling modes, identified in the edge of L-mode plasmas with strong edge current, drive the formation of an edge current hole and ejection of a current-carrying filament consistent with electromagnetic blob theory. Similar behavior is indicated with ELMs in H-mode plasmas.