Nonlinear Simulations of Peeling‐Ballooning Modes with Parallel Velocity Perturbation

Abstract

AbstractThe fast‐reconnection simulation of ELMs in high‐confinement mode tokamak discharges with non‐ideal physics effects has been reported by Xu, et al [1] with a minimum set of three‐field two‐fluid equations. Here we improve the simulation by adding the perturbed parallel velocity and Hall effect, then extend the model to a set of four‐field two‐fluid equations to describe the pedestal collapse with the BOUT++ simulation code. Compared to the previous results, we find that the perturbed parallel velocity can decrease the growth rate by 20.0%, and the ELM size is decreased by 12.1%. The Hall effect influences the linear growth rate effectively. Without perturbed parallel velocity, the Hall effect will increase the growth rate by 9.8%. It is increased by 19.1% if the parallel velocity is considered. These results are consistent with the qualitative theoretical analysis. In order to smooth the perturbed zigzags of the profiles of variables, we add the hyper‐diffusion terms in the equations. We use the hyper‐diffusion of pressure which does not affect the linear growth rate and the ELM structure obviously, but they can smooth the profiles effectively on grid scales. Last the effects of other differencing methods are discussed and we find that lower order method yeilds lower fluctuation level and smaller ELM size (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)