Dynamic Behavior of Peeling-Ballooning Modes in a Shifted-Circle Tokamak Equilibrium*

Progress in understanding edge localized modes (ELMs) has been made by investigating the stability properties of peeling-ballooning modes. We focus on the linear and nonlinear evolution of the peeling-ballooning modes over the entire spectrum in a shifted-circle tokamak equilibrium, using the extended-MHD code NIMROD. The TOQ-generated equilibrium models an H-mode plasma with a pedestal pressure profile and parallel driven edge currents. ~A vacuum region is prescribed by a resistivity profile that transitions from a small to very large value at a specified location. We manipulate the modes that govern the pedestal evolution, by changing this location. Ballooning-like instabilities dominate distant vacuum cases, whereas peeling mode physics is expected to dominate as the vacuum approaches the pedestal. An extensive nonlinear study is planned in addition to a linear analysis as functions of the pedestal parameters and vacuum location. We present our linear results and nonlinear computational comparisons between the peeling-dominated and ballooning-dominated mode evolution.