On Extending Simple but Exact 2-D Plasma - Magnetic Field Configurations

We have followed the Harris (1962) and Kan (1973) technique for obtaining self-consistent magnetic field and plasma structures and have constructed several exact, 2-D plasma - magnetic field configurations, including ones with X-points, where a Maxwellian plasma is consistent with the magnetic field. The models are restrictive: for example, the current is unidirectional and thereis no electric field. These and other restrictions can be removed through perturbation techniques and we give examples of how this can be done. We emphasize the usefulness of the generalized first invariant, the form it takes in regions of steep field gradients, and show how analytic drift equations can be derived that describe the guiding-point motions of the particles. The effects of the perturbations are obtained by including the drifts in the particle distribution functions and solving for the resulting modifications to the structure. This analysis of the interaction between the magnetic field and the local plasma can be used to help interpret particle and field observations in current sheet regions with steep gradients or in X-point structures, as in the magnetopause and tail current sheet. It should also help to improve our understanding of the kinetic behavior of the plasma and fields in these regions.