MHD simulation of resonant magnetic perturbations and ELMs

Resonant magnetic perturbations (RMP) applied by non-axisymmetric coils placed outside the plasma have been found effective in suppressing Edge Localized Modes (ELMs) in the DIII-D experiment. The experimental temperature profile is found to be less affected by the RMP than the density profile. Simulations with the M3D code indicate that plasma toroidal rotation has an essential effect on the RMP. When the rotation is below a threshold value, the magnetic field including the RMP is stochastic in the outer part of the plasma. The temperature is strongly affected by parallel thermal conduction, while the density is modified much less. At higher rotation speed, the RMP is screened from the plasma, and the temperature is hardly affected by the RMP. The density is perturbed at the plasma edge and accumulates near the magnetic separatrix x-point. When a poloidal rotation is added, or two-fluid diamagnetic drifts, the effect is further enhanced. The scaling of the screening effect with rotation shear and Lundquist number S will be discussed. In the absence of an RMP, unstable ELMs show a difference between temperature and density behavior during the nonlinear evolution, similar to that seen with the RMP. (author)