Does chaos matter in the plasma sheet?

Abstract

Can the average bulk flow of an ensemble of charged particles in Earth's plasma sheet still be described by adiabatic theory even if the ensemble contains a significant number of particles executing non-adiabatic motion? This is part of a broader spectrum of questions which ask if chaotic microscopic processes can be parametrized as macroscopic ones when ensemble averaged. Wolf and Pontius (1993) have shown that at least for a simple 2D, tail-like magnetic field configuration, the average particle drift speed of an appropriately chosen ensemble of particles, including those executing chaotic motion, is given correctly by the simple adiabatic guiding-center drift formula. Here, we extend the proof to 2${1\over2}$D magnetic fields (3 component, 2 spatial dependences) and include the effects of an electric field. The results of numerical test-particle simulations further show that the dispersion of particles about the mean drift speed tends to decrease due to the presence of chaotic particle scattering. Thus, we have shown that the standard way of representing particle transport in the inner magnetosphere, namely the isotropic pitch angle, bounce averaged drift formalism, is valid for the central plasma sheet despite the presence of non-adiabatic particle motion