The Diffusion Region in Collisionless Magnetic Reconnection

Hesse, Michael; Neukirch, T.; Schindler, K.; Кузнецова, М. М.; Zenitani, Seiji

doi:10.1007/s11214-010-9740-1

Cited by 144 publications

(139 citation statements)

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“…Specifically, we now know that reconnection is typically fast, 1 even though the rate may vary depending on the presence of magnetic islands, 2 and reconnection appears to be mediated by thermal inertia effects, which most prominently manifest themselves in form on nongyrotropic behavior of charged particles of all types, including electrons. 3,4 We further understand that the reconnection electric field is self-consistently required to maintain both current density and plasma pressure in the diffusion region, 5 and that a substantial component of outflow energy is in form of enthalpy flux. 6,7 Strictly speaking, however, symmetric systems are an exception, even though they are often seen as a good approximation to the night side of Earth's magnetosphere.…”

Section: Introductionmentioning

confidence: 98%

Aspects of collisionless magnetic reconnection in asymmetric systems

et al. 2013

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International audienceAsymmetric reconnection is being investigated by means of particle-in-cell simulations. The research has two foci: the direction of the reconnection line in configurations with nonvanishing magnetic fields; and the question why reconnection can be faster if a guide field is added to an otherwise unchanged asymmetric configuration. We find that reconnection prefers a direction, which maximizes the available magnetic energy, and show that this direction coincides with the bisection of the angle between the asymptotic magnetic fields. Regarding the difference in reconnection rates between planar and guide field models, we demonstrate that a guide field can provide essential confinement for particles in the reconnection region, which the weaker magnetic field in one of the inflow directions cannot necessarily provide

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Section: Introductionmentioning

confidence: 98%

Aspects of collisionless magnetic reconnection in asymmetric systems

et al. 2013

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“…However, over longer timescales these simulations reveal a new scenario in which flux ropes can be generated through secondary instabilities in the highly extended electron-scale current sheets that form nonlinearly during the onset of reconnection. These electron layers are a general feature of fast reconnection in collisionless plasmas and play a crucial role in breaking the frozen-in condition [1][2][3][4] . In sufficiently large systems, previous 2D simulations have demonstrated that these layers may become highly extended and form secondary magnetic islands [5][6][7][8][9][10] .…”

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Role of electron physics in the development of turbulent magnetic reconnection in collisionless plasmas

et al. 2011

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Magnetic reconnection releases energy explosively as field lines break and reconnect in plasmas ranging from the Earth's magnetosphere to solar eruptions and astrophysical applications. Collisionless kinetic simulations have shown that this process involves both ion and electron kinetic-scale features, with electron current layers forming nonlinearly during the onset phase and playing an important role in enabling field lines to break 1-4 . In larger two-dimensional studies, these electron current layers become highly extended, which can trigger the formation of secondary magnetic islands 5-10 , but the influence of realistic three-dimensional dynamics remains poorly understood. Here we show that, for the most common type of reconnection layer with a finite guide field, the three-dimensional evolution is dominated by the formation and interaction of helical magnetic structures known as flux ropes. In contrast to previous theories 11 , the majority of flux ropes are produced by secondary instabilities within the electron layers. New flux ropes spontaneously appear within these layers, leading to a turbulent evolution where electron physics plays a central role.Thin current layers are the preferred locations for magnetic reconnection to develop. The most common configuration in nature is guide-field geometry, where the rotation of magnetic field across the layer is less than 180 • . Present theoretical ideas of how reconnection proceeds in these configurations are deeply rooted in early analytical work 11 that, if correct, would imply a direct transition to three-dimensional (3D) turbulence due to a broad spectrum of interacting tearing instabilities. At the core of this idea is the notion that a spectrum of tearing instabilities develops across the initial current sheet for perturbations satisfying the local resonance condition. As these modes grow, the resulting magnetic islands would overlap, leading to stochastic magnetic-field lines and a turbulent evolution. Recently, this type of scenario was proposed as a mechanism for accelerating energetic particles during reconnection 12 . Similar ideas for generating turbulence have been studied in fusion plasmas 13 using resistive magnetohydrodynamics (MHD) and two-fluid 14 models. Alternatively, other researchers have imposed turbulent fluctuations within MHD models in an attempt to understand the consequences 15 . In either case, these results are not applicable to the highly collisionless environment of the magnetosphere, where reconnection is initiated within kinetic ion-scale current layers. The ability to study the self-consistent generation of turbulence during magnetic reconnection with first-principles 3D simulations has only become feasible in the past year.1 Los Alamos National Laboratory, Los Alamos, New Mexico 87545, USA, 2 University of California San Diego, La Jolla, California 92093, USA. *e-mail: daughton@lanl.gov. tearing instability gives rise to flux ropes as illustrated by an isosurface of the particle density coloured by the magnitude of the curr...

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“…Below the electron inertial length scale, even electrons are no longer frozen-in along the magnetic field lines. The electron inertial term and anisotropic electron pressure term have important roles [18,[26][27][28][29][30][31]. The reconnection rate is dominated by the Hall effect because of the electron inertial length being smaller than the ion inertial length.…”

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Electron dynamics in collisionless magnetic reconnection

Wang

Xie

et al. 2011

Chin. Sci. Bull.

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Magnetic reconnection provides a physical mechanism for fast energy conversion from magnetic energy to plasma kinetic energy. It is closely associated with many explosive phenomena in space plasma, usually collisionless in character. For this reason, researchers have become more interested in collisionless magnetic reconnection. In this paper, the various roles of electron dynamics in collisionless magnetic reconnection are reviewed. First, at the ion inertial length scale, ions and electrons are decoupled. The resulting Hall effect determines the reconnection electric field. Moreover, electron motions determine the current system inside the reconnection plane and the electron density cavity along the separatrices. The current system in this plane produces an out-of-plane magnetic field. Second, at the electron inertial length scale, the anisotropy of electron pressure determines the magnitude of the reconnection electric field in this region. The production of energetic electrons, which is an important characteristic during magnetic reconnection, is accelerated by the reconnection electric field. In addition, the different topologies, temporal evolution and spatial distribution of the magnetic field affect the accelerating process of electrons and determine the final energy of the accelerated electrons. Third, we discuss results from simulations and spacecraft observations on the secondary magnetic islands produced due to secondary instabilities around the X point, and the associated energetic electrons. Furthermore, progress in laboratory plasma studies is also discussed in regard to electron dynamics during magnetic reconnection. Finally, some unresolved problems are presented. Magnetic reconnection provides an effective mechanism for fast conversion of magnetic energy into plasma kinetic energy. Simultaneously, the topology of magnetic field changes [1][2][3]. First proposed by Giovanelli, magnetic reconnection is related to many explosive phenomena, such as solar flares, magnetospheric substorms, and disruptive instabilities in Tokamak plasmas [4][5][6][7][8]. Giovanelli thought discharge phenomena would occur around the neutral line or point where the magnetic field vanishes, an idea that could be very important in solar-flare production [9]. In 1958, Dungey first introduced the concept of "magnetic reconnection" , applying it in the construction of the open *Corresponding author (email: qmlu@ustc.edu.cn) Earth magnetosphere model [10]. The first magnetic reconnection model was proposed by Sweet and Parker, separately. In this model, plasma and magnetic field flow into the center of the current sheet from both sides where magnetic field lines are cut off and reconnected. Magnetic energy is converted into plasma kinetic energy; energized plasma then flows out of the region from both ends [11,12]. However, the predicted reconnection rate in this model is so low that it is unable to account for the explosive phenomena in space. Petschek improved the Sweet-Parker model and suggested that magnetic reconnecti...

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The Diffusion Region in Collisionless Magnetic Reconnection

Cited by 144 publications

References 46 publications

Aspects of collisionless magnetic reconnection in asymmetric systems

Aspects of collisionless magnetic reconnection in asymmetric systems

Role of electron physics in the development of turbulent magnetic reconnection in collisionless plasmas

Electron dynamics in collisionless magnetic reconnection

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