Hybrid kinetic-MHD model of RMP interaction with tokamak plasmas

We present a hybrid kinetic–MHD approach realized within the code MEPHIT for the linear modeling of the interaction of resonant magnetic perturbations (RMPs) with tokamak plasmas. The model uses an iterative approach, where the solution of Ampère’s law in realistic device geometry is combined with the computation of plasma response currents to a given magnetic perturbation. The latter computation employs the ideal MHD model in most of the plasma volume, and a 1D collisional kinetic model in the resonant layers centered around rational flux surfaces. Within a 1D kinetic model, a straight inhomogeneous plasma cylinder geometry is assumed, and the finite Larmor radius expansion of the plasma response current and charge densities up to second order is employed. The hybrid kinetic–MHD model is applied to RMPs in ASDEX Upgrade experiments on edge-localized mode suppression and compared to the results of the code GPEC used in the ideal MHD limit. In particular, the new hybrid model allows the estimation of the size of an RMP-induced magnetic island well in the case where the electron shielding current is nearly eliminated by quasilinear effects due to the electron fluid resonance. Moreover, the hybrid approach developed here easily permits further incorporation of more detailed and accurate kinetic models of the resonant layer.