Abstract
Hybrid-Vlasov–Maxwell simulations of magnetized plasma turbulence including non-linear electron-inertia effects in a generalized Ohm's law are presented. When fluctuation energy is injected on scales sufficiently close to ion-kinetic scales, the ions efficiently become de-magnetized and electron-scale current sheets largely dominate the distribution of the emerging current structures, in contrast to the usual picture, where a full hierarchy of structure sizes is generally observed. These current sheets are shown to be the sites of electron-only reconnection (e-rec), in which the usual electron exhausts are unaccompanied by ion outflows and which are in qualitative agreement with those recently observed by MMS in the Earth's turbulent magnetosheath, downstream of the bow shock. Some features of the e-rec phenomenology are shown to be consistent with an electron magnetohydrodynamic description. Simulations suggest that this regime of collisionless reconnection may be found in turbulent systems where plasma processes, such as micro-instabilities and/or shocks, overpower the more customary turbulent cascade by directly injecting energy close to the ion-kinetic scales.
Highlights
Accurate in situ satellite measurements of plasma fluctuations and particle distribution functions in the heliosphere are today the primary experimental tool for the study of plasma turbulence (e.g., [1,2,3]) and magnetic reconnection (e.g., [4, 5])
Using numerical simulations of kinetic plasma turbulence in a hybrid Vlasov–Maxwell model that includes fully non-linear electron-inertia effects, we have demonstrated for the first time that short CSs in which electron-only reconnection takes place can naturally develop within kinetic plasma turbulence at β ∼ 1 when fluctuations are injected on a range of wavenumbers near ion-kinetic scales
All CSs showing clear evidence of ongoing magnetic reconnection exhibit electron exhausts that are unaccompanied by ion outflows, with the ions being decoupled from the magnetic-field and electron dynamics almost everywhere
Summary
Accurate in situ satellite measurements of plasma fluctuations and particle distribution functions in the heliosphere are today the primary experimental tool for the study of plasma turbulence (e.g., [1,2,3]) and magnetic reconnection (e.g., [4, 5]). While e-rec has been recently shown to occur in kinetic simulations of magnetic reconnection when a single electron-scale CS is ad-hoc initialized [12] or after a quasi-parallel shock [13], it is difficult to explain e-rec in the context of a classical turbulent cascade, in which turbulent energy is e-rec in Plasma Turbulence transferred conservatively from magneto-fluid scales down to ion-kinetic scales, thereby coupling to the ion dynamics in the usual way [4, 14,15,16,17,18,19,20,21,22,23,24]. We show that the physics underlying some features of the e-rec phenomenology can be described by the equations of electron magnetohydrodynamics (EMHD; [30,31,32])
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