Nonlinear excitation of coherent structures and associated cross-field transport in a magnetized plasma

Abstract

Nonlinear interactions between zero-frequency electrostatic convective cells (CCs)/zonal flows (ZFs) and magnetostatic (MS) modes in a magnetoplasma are numerically investigated. These nonlinearly coupled flute-like modes can be spontaneously excited, and contribute significantly to the anomalous cross-field transport. While they are degenerate in a linear regime and form purely damped modes, their mutual nonlinear interactions give rise to large-scale coherent structures through a turbulent relaxation that leads to a self-organization via an inverse cascade. Remarkably, we find that nonlinear excitations of large-scale structures give rise to an effective cross-field diffusion coefficient that varies initially as ∼ t 1 / 2 with time, and enhances the transport level dramatically.