The impact of n=0 zonal flows and zonal fields on ELM crashing dynamics*

To solve low-n and zonal components of potential and magnetic field, field solver using 3D hypre is implemented in BOUT++ framework. Both linear and nonlinear simulations show that the simulation results, such as linear growth rate and ELM size, are comparable for the cases without zonal effects by using original 2D and the new 3D hypre solver. Nonlinear simulations are performed with a shifted circular equilibrium to investigate the zonal flows and zonal magnetic fields effects for ELM crashing dynamics using 3D hypre solver. The interplay between fluctuation driven toroidal axisymmetric flows (n=0) and peeling-ballooning mode turbulence after the pedestal collapse is studied. A dramatic change of dynamics takes place during ELM crashing. The strong flow shear suppresses the radial transport of pressure filaments, and the ELM size decreases as the zonal flows increases. When the ideal peeling-ballooning mode are stabilized after the initial ELM crash, a new instability is developed due to a strong excitation of zonal vorticity, resulting in a series of secondary crashes. The presence of subsidiary bursts after a main crash increases the effective crash time and energy loss. While with zonal fields effects, the pedestal will get into completely stabilized phase after the secondary crash. Analyses in this paper indicate that n=0 zonal flow and zonal magnetic field effects play an important role on ELM crashing and pedestal transport processing.