Equilibrium selection via current sheet relaxation and guide field amplification

Although there is a continuous spectrum of current sheet equilibria, how a particular equilibrium is selected by a given system remains a mystery. Yet, only a limited number of equilibrium solutions are used for analyses of magnetized plasma phenomena. Here we present the exact process of equilibrium selection, by analyzing the relaxation process of a disequilibrated current sheet under a finite guide field. It is shown via phase-space analyses and particle-in-cell simulations that the current sheet relaxes in such a way that the guide field is locally amplified, yielding a mixed equilibrium from the spectrum. Comparisons to spacecraft observations and solar wind current sheet statistics demonstrate that such mixed equilibria are ubiquitous and exist as underlying local structures in various physical environments. Magnetized plasmas display continuous spectra of current-sheet equilibria. How they select a particular equilibrium is not well understood. Now, equilibrium selection in magnetized plasmas is studied by analytical theory, particle-in-cell simulations and spacecraft observations, highlighting the role of current-sheet relaxation processes.

Automated summary

Although a continuous spectrum of current sheet equilibria exists, how a particular equilibrium is selected by a system remains unknown. This study reveals the exact process of equilibrium selection by analyzing the relaxation process of an unequilibrated current sheet with a finite guide field. The results demonstrate that the current sheet relaxes in a way that locally amplifies the guide field, leading to a mixed equilibrium. Comparisons with spacecraft observations and solar wind current sheet statistics show that such mixed equilibria are common and act as underlying local structures in various physical environments.