Computing nonlinear magnetohydrodynamic edge localized instabilities in fusion plasmas

The onset and nonlinear evolution of Edge Localized Modes (ELMs) in toroidally confined plasmas are known to shed thermal energy from the edge of the confinement region, and may also affect the core plasma through nonlinear mode coupling. The physics of this process is not well understood, although the concomitant large bursts of thermal energy transport are a major concern for future burning plasma experiments. The evolution of ELMs is inherently nonlinear and analytic approaches are limited by the complexity of the problem. Save a handful of recent important theoretical works, the nonlinear consequences of ELMs are mainly unexplored. Recent developments in the NIMROD code [http://nimrodteam.org] have enabled the computational study of ELMs in tokamaks in the extended magnetohydrodynamic (MHD) framework, and a new initiative was formed to understand the basic physics of their nonlinear evolution. The results of these investigations are presented for both model equilibria and accurate reconstructions from the DIII-D experiment at General Atomics [http://fusion.gat.com/diii-d/]. These results show a filamentary high temperature structure propagating radially outward, which is strongly damped by experimentally relevant toroidal flow shear. Two fluid and gyroviscous terms are included linearly as a preliminary indication of these important physical effects, and stabilization of higher wave number modes is observed.