Statistical properties of turbulent fluctuations associated with electron-only magnetic reconnection

Arrò, Giuseppe; Califano, Francesco; Lapenta, G.

doi:10.1051/0004-6361/202038696

Cited by 13 publications

(5 citation statements)

References 29 publications

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“…Idealized PIC simulations of laminar magnetic reconnection, in which the length of the reconnecting current sheets were artificially varied by changing the size of the simulation domain, have shown that if the length of the current sheet along the outflow direction is less than ∼ 40d i then the ions will only partially couple to the reconnected magnetic field, resulting in reduced ion jet speeds relative to expectations, and if the the current sheet length is less than ∼ 10d i , the ion jets are virtually non-existent and are consistent with electrononly reconnection 78 . More recent PIC and Vlasov simulations of plasma turbulence have also begun to confirm that turbulent dynamics can generate electron-only reconnection [81][82][83] .…”

Section: Introductionmentioning

confidence: 98%

Turbulence-driven magnetic reconnection and the magnetic correlation length: Observations from Magnetospheric Multiscale in Earth's magnetosheath

et al. 2022

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Turbulent plasmas generate a multitude of thin current structures that can be sites for magnetic reconnection. The Magnetospheric Multiscale (MMS) mission has recently enabled the detailed examination of such turbulent current structures in Earth's magnetosheath and revealed that a novel type of reconnection, known as electron-only reconnection, can occur. In electron-only reconnection, ions do not have enough space to couple to the newly reconnected magnetic fields, suppressing ion jet formation and resulting in thinner sub-proton-scale current structures with faster super-Alfvénic electron jets. In this study, MMS observations are used to examine how the magnetic correlation length (λ C ) of the turbulence, which characterizes the size of the largescale magnetic structures and constrains the length of the current sheets formed, influences the nature of turbulence-driven reconnection. We systematically identify 256 reconnection events across 60 intervals of magnetosheath turbulence. Most events do not appear to have ion jets; however, 18 events are identified with ion jets that are at least partially coupled to the reconnected magnetic field. The current sheet thickness and electron jet speed have a weak anti-correlation, with faster electron jets at thinner current sheets. When λ C < ∼ 20 ion inertial lengths, as is typical near the sub-solar magnetosheath, a tendency for thinner current sheets and potentially faster electron jets is present. The results are consistent with electron-only reconnection being more prevalent for turbulent plasmas with relatively short λ C , and may be relevant to the nonlinear dynamics and energy dissipation in turbulent plasmas.

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Section: Introductionmentioning

confidence: 98%

Turbulence-driven magnetic reconnection and the magnetic correlation length: Observations from Magnetospheric Multiscale in Earth's magnetosheath

et al. 2022

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“…It is known that plasma turbulence naturally tends to generate magnetic field shears associated with intense current sheets (Servidio et al 2009(Servidio et al , 2010. The role of these structures in turbulence has been extensively studied in relation to the occurrence of energetic phenomena, such as reconnection, that can influence the properties of the turbulent cascade and of dissipation Franci et al 2017;Dong et al 2018;Comisso et al 2018;Arrò et al 2020). Here we have shown that electron velocity shears are also spontaneously generated by the turbulence and their disruption via the EKHI supports the cascade of energy from large to sub-ion scales, producing kinetic scale EVMHs that possibly contribute to dissipation.…”

Section: Discussionmentioning

confidence: 99%

Generation of sub-ion scale magnetic holes from electron shear flow instabilities in plasma turbulence

Arrò

Pucci

Califano

et al. 2023

Preprint

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<p>Magnetic holes are coherent structures associated with a strong depression in the magnetic field amplitude. Such structures are ubiquitous in space plasmas and are observed in the solar wind, in planetary bow shocks and magnetosheaths, in the Earth's magnetotail and around comets. Magnetic holes may have very different sizes and properties. The largest ones have a size of hundreds of ion gyroradii while the smallest ones are sub-ion scale structures of the order of a few electron gyroradii. The drop in magnetic field amplitude associated with magnetic holes is often sustained by an increase in plasma density and enhanced ion and electron temperature anisotropies, with temperatures that are typically higher in the plane perpendicular to the local magnetic field. These properties seem to suggest that the generation of magnetic holes may result from the nonlinear evolution of mirror modes whose growth is fed by perpendicular temperature anisotropies and that are characterized by anticorrelated magnetic field and density perturbations. Some observational and numerical studies seem to support the idea of a scenario in which magnetic holes are generated by the mirror instability but in many cases this picture is not consistent with observations, especially in the case of sub-ion scale magnetic holes for which a number of possible generation mechanisms have been considered. Hence, the origin of magnetic holes is still controversial and under debate.&#160;</p> <p>Plasma turbulence is also known as a driver for the generation of coherent structures and may play a key role in the formation of magnetic holes, especially in the solar wind and in the Earth's magnetosheath that are in a turbulent state. Indeed, numerical simulations of plasma turbulence show that sub-ion scale magnetic holes can develop self-consistently out of small scale magnetic fluctuations that locally reduce the magnetic field amplitude and trap hot electrons. However, it is still unclear how such small scale fluctuations can emerge in a turbulent plasma where energy is typically injected at large scales. In this work, we study the formation of sub-ion scale magnetic holes by means of fully kinetic particle-in-cell simulations of plasma turbulence. We show that by injecting energy at scales relatively large with respect to ion scales, the turbulence naturally tends to generate sub-ion scale electron velocity shear layers associated with elongated magnetic field grooves. These elongated magnetic dips then become unstable and break up into sub-ion scale magnetic holes characterized by an intense azimuthal electron current and a strong perpendicular electron temperature anisotropy. We show that the properties of magnetic holes generated by this mechanism are consistent with satellite observations. Our results may provide a possible explanation of how magnetic holes develop in a realistic turbulent environment.</p>

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“…An immediate application of this novel theory is to estimate energy dissipation in localized structures (e.g., reconnecting current sheets) frequently reported in numerical simulations [55] and spacecraft observations in the near-Earth space [28,56]. Indeed, even if the theory is based on a fluid (HMHD) model, the fact that π (x) is shown to reflect local dissipation (within the aforementioned assumptions) regardless of the explicit form of the dissipation operators makes it particularly relevant to collisionless plasmas where the damping of the fluid and electromagnetic fluctuations is believed to originate from kinetic processes that would show up in the moment equation as complex damping operators d ν , d η .…”

Section: Discussionmentioning

confidence: 99%

Local cascade and dissipation in incompressible Hall magnetohydrodynamic turbulence: the Coarse-Graining approach

Manzini,

Sahraoui,

Califano

et al. 2022

Preprint

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We derive the coarse-graining (CG) equations of incompressible Hall Magnetohydrodynamics (HMHD) turbulence to investigate the local (in space) energy cascade rate as a function of the filtering scale . First, the CG equations are space averaged to obtain the analytical expression of the mean cascade rate. Its application to 3 dimensional (3D) simulations of (weakly compressible) HMHD shows a cascade rate consistent with the value of the mean dissipation rate in the simulations and with the classical estimates based on the "third-order" law. Furthermore, we developed an anisotropic version of CG that allows us to study the magnitude of the cascade rate along different directions with respect to the mean magnetic field. Its implementation on the numerical data with moderate background magnetic field shows a weaker cascade along the magnetic field than in the perpendicular plane, while an isotropic cascade is recovered in the absence of a background field. The strength of the CG approach is further revealed when considering the local-in-space energy transfer, which is shown theoretically and numerically to match at a given position x, when locally averaged over a neighboring region, the (quasi-)local dissipation. Prospects of exploiting this new model to investigate local dissipation in spacecraft data are discussed. II. COARSE-GRAINED INCOMPRESSIBLE HMHD EQUATIONSWe introduce the notion of a coarse grained (CG) measurement of a field f with a scale resolution . We choose a kernel function G normalized to one drG(r) = 1, centered drrG(r) = 0 and with variance of order unity

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Statistical properties of turbulent fluctuations associated with electron-only magnetic reconnection

Cited by 13 publications

References 29 publications

Turbulence-driven magnetic reconnection and the magnetic correlation length: Observations from Magnetospheric Multiscale in Earth's magnetosheath

Turbulence-driven magnetic reconnection and the magnetic correlation length: Observations from Magnetospheric Multiscale in Earth's magnetosheath

Generation of sub-ion scale magnetic holes from electron shear flow instabilities in plasma turbulence

Local cascade and dissipation in incompressible Hall magnetohydrodynamic turbulence: the Coarse-Graining approach

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