Plasma Response to Magnetic Perturbations Relevant to Edge Localised Modes

Edge Localized Modes (ELMs) are repetitive eruptions of particles and energy which occur in many high confinement mode plasmas. In present devices the power loads delivered to the divertor during an ELM do not pose a serious problem. However, extrapolations to the ITER tokamak suggest that divertor lifetimes maybe reduced below acceptable levels. The application of Resonant Magnetic Perturbations (RMPs) to the plasma has successfully demonstrated ELM mitigation and suppression, under a number of operating scenarios. However, the physical mechanism by which mitigation and suppression is achieved is still not well understood. Furthermore many questions remain concerning the threshold perturbation strength and perturbation spectrum required.
Models and theory initially developed for error field analysis are increasingly being used, and developed, to explain the plasma response to RMPs. The BOUT++ code is tested against a selection of linear layer problems. This is the first step in applying the code to model the self consistent plasma response to RMPs. The code is demonstrated to be consistent with theory in all cases modeled. In addition for the first time the importance of radial grid packing is considered in obtaining accurate simulations to RMP experiments.
A novel multi-surface model is developed, and a single and two surface model is applied to the neighborhood of the radial location at which the perpendicular electron rotation is zero. Bifurcation windows are produced which are in qualitative agreement with ELM suppression q95 windows. Bifurcation locusts are also shown to be in qualitative agreement with the experimental spectrum results of M. E. Fenstermacher et at, Nucl Fusion 48:122001, 2008