Observation of RMP-Induced Edge Kink-Like Modes and Their Effects on Density Pump-Out in KSTAR

The application of resonant magnetic perturbations (RMPs) in tokamaks commonly leads to a decrease in plasma density; this RMP-induced side effect is referred to as the ’density pump-out’ effect. In KSTAR, the density pump-out effect is shown to be accompanied by kink-like modes at the plasma edge. These modes align in phase with the applied RMPs, as measured by multiple diagnostics systems. In particular, a poloidally nonuniform plasma surface displacement caused by these modes was accurately captured using a novel image processing technique predicted by previous studies [1]. When the edge kink-like modes are present, the symmetry-breaking effect due to the displacement is found to be much larger than that of the applied RMPs themselves near the plasma boundary. Since these modes distort the equilibrium magnetic flux surfaces, the modification in the magnetic field strength B variation on the distorted surface can significantly enhance neoclassical particle transport [2]. In this study, our work focuses on calculating the neoclassical particle transport through B variation due to the edge kink-like modes. Through 1D transport analysis, we demonstrate that the enhanced electron particle transport, driven by the symmetry-breaking effect due to the edge kink-like modes, is large enough to explain the experimentally observed density pump-out effect by RMPs.