Drive of a long-lived vortex-flow pattern by coupling to zonal flows in presence of resonant magnetic perturbations

Abstract

The working hypothesis for the origin of edge-localized-mode stabilization is that Resonant Magnetic Perturbations (RMPs) increase transport in the pedestal, thus lowering the pressure gradient below the ideal MHD threshold. Large-scale vortex-flows matching the RMP helicity were observed experimentally [N. Vianello et al., Plasma Phys. Controlled Fusion 57, 014027 (2015)]. We derive and solve numerically a 1D model for the generation of long-lived vortex-flows in presence of RMPs. We show that, in presence of RMPs, zonal flows are damped and partially transfer their energy to a resonant vortex-flow pattern. The resulting vortex-flow has a multiscale nature with a fast-varying fine-structure set by zonal flows and a slowly-varying radial envelope with a resonant character. The model predicts that the saturated vortex-flow energy E scales with RMP amplitude as E∼δBrBα with α≃1.9. This novel type of nonlinearly driven non-axisymmetric flow has a radial—streamer like—component, and is therefore a candidate for increased convective transport.