Relaxation of current-carrying flux tubes and flux rope formation*

Flux ropes are ubiquitous structures in space and laboratory plasma environments. Although their equilibrium states have been extensively studied, how they relax from non-equilibrium states is an important process that has been relatively less explored. By analogy to previous studies on current sheets, particle orbits are analyzed and their phase-space trajectories are studied. Analytical calculations show that orbital transitions must occur in a non-equilibrium current sheet and leave distinct footprints in the phase-space distributions. These footprints are verified by kinetic simulations of disequilibrated current sheets, confirming the relaxation process. It is shown that any small parallel current will relax to a flux rope configuration.