Three-Dimensional Reconnection and Turbulence in the Outer Heliosphere

Abstract:

In the outer heliosphere, close to the heliopause, we can expect the heliospheric current sheet to form a region of closely-packed, thin current sheets. These structures may be subject to an ion-kinetic tearing instability, and hence generate magnetic islands and hot populations of ions associated with magnetic reconnection. It has been suggested that reconnection processes in this environment have important implications for local particle transport, influencing the porosity of the sectored heliosheath, and for the generation of anomalous cosmic rays via acceleration at reconnection sites. We study this complex environment by means of three-dimensional hybrid simulations over long time scales, in order to capture the evolution of the system from linear growth of the tearing instability at early times, to a fully developed turbulent cascade at late times. Simulations are conducted using both force-free and Harris current sheet equilibria, with varying plasma beta and guide field angle. We discuss the evolution of the magnetic topology, and how changes in the initial conditions affect reconnection rates, particle acceleration, cross-boundary transport and magnetic spectra. We also examine the effect of including an energetic population of interstellar H+ pick-up ions. Finally, given the turbulent end state in the simulations, we also investigate the multiple current sheet system as a general scenario for driving turbulence, and as an alternative to the common methods for simulating decaying turbulence.