Plasma transport in the Io torus: The importance of microscopic diffusion

Abstract

We consider the question of whether the distribution of mass in the Io plasma torus is consistent with the concept of interchange eddy transport. Specifically, the flux tube content exhibits a gradual decrease with increasing radial distance from the source near Io without any evidence for substantial density irregularity associated with the plasma source or loss. Using a simple one dimensional numerical model to simulate macroscopic interchange eddy transport, we demonstrate that this smooth equilibrium distribution of mass can occur but only with the inclusion of a minimal level of small scale microscopic mixing at a rate approaching Bohm diffusion. Otherwise the system exhibits a chaotic appearance which never approaches an equilibrium distribution. We discuss various physical mechanisms for the microscopic diffusion process which is required to provide a sufficiently rapid mixing of material between the macroscopic eddies.