Internal rotation of ELM filaments on NSTX

Edge localized modes (ELMs) are a threat to tokamaks due to their high heat and particle loads on the plasma facing components (PFCs). A significant portion of this energy is carried and deposited by the emerging ELM filaments, whose dynamics are directly connected to their impact. Therefore, understanding their underlying physics is important for the operation of future fusion reactors. We extend our knowledge of ELM filaments by investigating their internal rotation around their own axis. Our analysis of gas-puff imaging (GPI) data on NSTX show that ELM filaments are characterized by internal rotation in the direction of the ion-gyro motion with 15.2krad/s median angular velocity. The characteristic size of the ELM filament was also assessed and found to be similar to the blobs emerging in intermittent SOL turbulence. A nearly linear trend was found between the angular velocity of the ELM filament and both its radial velocity and its distance from the separatrix, as well. An analytical model called the shear-induced rotation model was identified as a candidate for explaining the physics of the observations. Our results show that the modelled mechanism could significantly influence the rotation of the ELM filament, however, it cannot be a sole contributor.