Turbulent transport in 2D collisionless guide field reconnection

TL;DR

This study investigates turbulence-driven anomalous transport in 2D collisionless guide field reconnection using Particle-in-Cell simulations, revealing electrostatic turbulence localized at the separatrix and its role in effective resistivity.

Contribution

It provides detailed analysis of turbulence excitation and transport mechanisms in guide-field reconnection, with validation against theoretical and observational data.

Findings

Turbulence is most intense at the low density separatrix region.

Electrostatic streaming instabilities drive patchy turbulence.

Anomalous resistivity can be modeled by an effective collision frequency.

Abstract

Transport in collisionless plasmas is usually called anomalous, being due to the interaction between the particles and the self-generated turbulence by their collective interactions. Because of its relevance for astrophysical and space plasmas, we explore the excitation of turbulence in current sheets prone to component- or guide-field reconnection, a process not well understood, yet. We analyze the anomalous transport properties by using 2.5D Particle-in-Cell (PiC) code simulations. We split off the mean, slow variation (in contrast to the fast turbulent fluctuations) of the macroscopic observables and determine the main transport terms of the generalized Ohm's law. We verify our findings by comparing with the independently determined slowing-down rate of the macroscopic currents and with the transport terms obtained by the first order correlations of the turbulent fluctuations. We find that the turbulence is most intense in the "low density" separatrix region of guide-field reconnection. It is excited by streaming instabilities, it is mainly electrostatic, "patchy" in space and so is the associated quasi-periodic anomalous transport. The remaining irreversible anomalous resistivity can be parametrized by an effective collision frequency ranging from the local ion-cyclotron to the lower-hybrid frequency. The contributions to the parallel and the perpendicular (to the magnetic field) components of the slowly varying, DC-electric fields, balanced by the turbulence, are similar. This anomalous electric field is, however, smaller than the contributions of the off-diagonal pressure and electron inertia terms of the Ohm's law. This result can now be verified by in-situ measurements of the turbulence, in and around the magnetic reconnection regions of the Earth's magnetosphere by the multi-spacecraft mission MMS and in laboratory experiments like MRX and VINETA-II.