The Effect of Externally Applied Magnetic Perturbations on NSTX Edge Turbulence

We report on a study of the structure and motion of the edge turbulence of NSTX when non-axisymmetric magnetic perturbations are applied. For this study, the turbulence that occurs in the presence of these perturbations is compared to the turbulence seen when these 3D fields are not present using imaging data from the gas puff imaging (GPI) diagnostic. When magnetic perturbations resonate with a particular magnetic surface, usually at the plasma edge, they are referred to as resonant magnetic perturbations (RMPs). RMPs can be used to mitigate damaging edge instabilities called edge localized modes (ELMs) that are found in the high confinement operating mode of tokamaks. The GPI diagnostic uses a puff of neutral deuterium gas to increase the local D-alpha emissions which allows for improved imaging of the edge turbulence. The imaging data consists of high speed movies of the plasma edge taken at 400,000 frames/second. Understanding how 3D fields effect edge transport will lead to a greater understanding of the plasma response to these 3D fields.