Turbulent transport in 2D collisionless guide field reconnection

Abstract

Transport in hot and dilute, i.e., collisionless, astrophysical and space plasmas is called "anomalous". This transport is due to the interaction between the particles and the self-generated turbulence by their collective interactions. The anomalous transport has very different and not well known properties compared to the transport due to binary collisions, dominant in colder and denser plasmas. Because of its relevance for astrophysical and space plasmas, we explore the excitation of turbulence in current sheets prone to componentor guide-field reconnection, a process not well understood yet. This configuration is typical for stellar coronae, and it is created in the laboratory for which a 2.5D geometry applies. In our analysis, in addition to the immediate vicinity of the X-line, we also include regions outside and near the separatrices. We analyze the anomalous transport properties by using 2.5D Particle-in-Cell 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 (due to a net momentum transfer from particles to waves) 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, is mainly electrostatic and "patchy" in space, and so is the associated anomalous transport. Parts of the energy exchange between turbulence and particles are reversible and quasi-periodic. The remaining irreversible anomalous resistivity can be parametrized by an effective collision rate 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. This article may be downloaded for personal use only. Any other use requires prior permission of the author and the American Institute of Physics. The following article appeared in P.A. Muñoz, J. Büchner and P. Kilian, Physics of Plasmas 24, 022104 (2017), and may be found at http://dx.

Kinetic turbulence in fast three-dimensional collisionless guide-field magnetic reconnection

“…This instability is relevant to understand the consequences of the self-generated turbulence in reconnection, because it can produce anomalous resistivity and thus balance the reconnection electric field associated to magnetic reconnection [80,81]. Even though in 2.5D fully-kinetic reconnection simulations this anomalous resistivity could not be found [82], other 3D fully-kinetic reconnection simulations provided some positive evidence [80,[83][84][85][86].…”

How anomalous resistivity accelerates magnetic reconnection

“…... denotes the ensemble average of the turbulence properties. is a fundamental problem in both plasma physics and space physics and is a subject of debate for nearly half a century 34,37,[42][43][44][45][46][47][48][49][50][51][52][53] . The problem is particularly difficult because AR and AV are highly nonlinear processes which take part in the even more complex magnetic reconnection processes.…”

“…AR 40 is induced by ES instabilities, arising from ion-electron drag, and AV 41 is induced by EM instabilities, arising from anomalous momentum transport. Whether AR and AV can facilitate fast magnetic reconnection in collisionless plasma (if so, how it is achieved) is a fundamental problem in both plasma physics and space physics and is a subject of debate for nearly half a century 34,37,[42][43][44][45][46][47][48][49][50][51][52][53] . The problem is particularly difficult because AR and AV are highly nonlinear processes which take part in the even more complex magnetic reconnection processes.…”

A Brief Review on Particle Acceleration in Multi-island Magnetic Reconnection

“…In 3D MR, it is almost unavoidable that various kinetic instabilities are triggered. This results in plasma heating that may suppress the generation of a power-law energy distribution function [59,45,46,74]. How to reconcile this issue with the observed power-law spectra is probably the key to understand particle acceleration in solar flares and solar wind.…”