A Time-Dependent Model for Magnetic Reconnection in the Presence of a Separator

Wilmot-Smith, A. L.; Hornig, G.

doi:10.1088/0004-637x/740/2/89

Cited by 20 publications

(29 citation statements)

References 35 publications

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“…In a similar calculation to that detailed in Sect. 5 of Wilmot-Smith & Hornig (2011), it is possible to estimate the reconnection rate of our separator reconnection event; for the chosen parameters, this is approximately 8.85×10 7 V. These values agree well with the reconnection rates determined from numerical experiments of separator reconnection. As an example, the reconnection rate and lengthscales used in our study fall exactly within the range of rates and scales recovered from a dynamic flux emergence experiment studied in Parnell et al (2010b) which yielded multiple magnetic separators, strengthening our conclusion that the electric fields and reconnection event studied here reproduce behaviour which is expected to occur within the solar atmosphere.…”

Section: Discussionsupporting

confidence: 77%

“…Our model can be broadly split into two parts: a (timedependent) large-scale electromagnetic field environment, into Wilmot-Smith & Hornig (2011). A black (white) sphere indicates the location of the upper (lower) null, the fan plane of which is seen in blue (orange) while the spines of both nulls are shown as thick black lines (due to the fan plane transparency, these lines adopt the colour of any fan planes they pass behind).…”

Section: Model Setupmentioning

confidence: 99%

“…Building on experiments by Haynes et al (2007) and Parnell (2007), recent work has highlighted that multiple magnetic separators may exist within a given magnetic environment at any given time (Parnell et al 2010a) and that separator reconnection is an important and fundamental process when emerging magnetic flux interacts with overlying magnetic field (Parnell et al 2010b). More recently, Wilmot-Smith & Hornig (2011) have shown that even simple magnetic configurations may evolve into configurations containing multiple separators.…”

Section: Introductionmentioning

confidence: 99%

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Particle acceleration at a reconnecting magnetic separator

Threlfall

Neukirch

Parnell

et al. 2015

A&A

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Context. While the exact acceleration mechanism of energetic particles during solar flares is (as yet) unknown, magnetic reconnection plays a key role both in the release of stored magnetic energy of the solar corona and the magnetic restructuring during a flare. Recent work has shown that special field lines, called separators, are common sites of reconnection in 3D numerical experiments. To date, 3D separator reconnection sites have received little attention as particle accelerators. Aims. We investigate the effectiveness of separator reconnection as a particle acceleration mechanism for electrons and protons. Methods. We study the particle acceleration using a relativistic guiding-centre particle code in a time-dependent kinematic model of magnetic reconnection at a separator. Results. The effect upon particle behaviour of initial position, pitch angle, and initial kinetic energy are examined in detail, both for specific (single) particle examples and for large distributions of initial conditions. The separator reconnection model contains several free parameters, and we study the effect of changing these parameters upon particle acceleration, in particular in view of the final particle energy ranges that agree with observed energy spectra.

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Section: Discussionsupporting

confidence: 77%

Section: Model Setupmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Particle acceleration at a reconnecting magnetic separator

Threlfall

Neukirch

Parnell

et al. 2015

A&A

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“…In 3-D, reconnection has been shown to occur at a multitude of sites, such as at topological features including 3-D null points (locations where all three components of the magnetic field equal zero) [e.g., Craig et al, 1995;Pontin et al, 2004Pontin et al, , 2005Pontin and Galsgaard, 2007;Priest and Pontin, 2009;Masson et al, 2009;Pontin et al, 2011] and magnetic separators (special field lines that link pairs of 3-D null points) [e.g., Priest and Titov, 1996;Longcope and Cowley, 1996;Longcope, 2001;Parnell et al, 2010aParnell et al, , 2010bWilmot-Smith and Hornig, 2011] or at the geometrical features known as quasi-separatrix layers (regions of magnetic field, which at one end are closely anchored but at the other end are anchored far apart) [e.g., Priest and Démoulin, 1995;Demoulin et al, 1996Demoulin et al, , 1997Aulanier et al, 2005Aulanier et al, , 2006 and in twisted or braided flux tubes [e.g., Galsgaard and Nordlund, 1996, 1997a, 1997bGalsgaard, 2006a, 2006b;Wilmot-Smith and De Moortel, 2007;Browning et al, 2008;Hood et al, 2009;Bareford et al, 2013].…”

Section: Introductionmentioning

confidence: 99%

Spontaneous reconnection at a separator current layer: 1. Nature of the reconnection

Stevenson

Parnell

2015

JGR Space Physics

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Magnetic separators, which lie on the boundary between four topologically distinct flux domains, are prime locations in three‐dimensional magnetic fields for reconnection, especially in the magnetosphere between the planetary and interplanetary magnetic fields and also in the solar atmosphere. Little is known about the details of separator reconnection, and so the aim of this paper, which is the first of two, is to study the properties of magnetic reconnection at a single separator. Three‐dimensional, resistive magnetohydrodynamic numerical experiments are run to study separator reconnection starting from a magnetohydrostatic equilibrium which contains a twisted current layer along a single separator linking a pair of opposite‐polarity null points. The resulting reconnection occurs in two phases. The first is short involving rapid reconnection in which the current at the separator is reduced by a factor of around 2.3. Most (75%) of the magnetic energy is converted during this phase, via Ohmic dissipation, directly into internal energy, with just 0.1% going into kinetic energy. During this phase the reconnection occurs along most of the separator away from its ends (the nulls) but in an asymmetric manner which changes both spatially and temporally over time. The second phase is much longer and involves slow impulsive bursty reconnection. Again, Ohmic heating dominates over viscous damping. Here the reconnection occurs in small localized bursts at random anywhere along the separator.

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“…This also ties in nicely with the separator model of Wilmot-Smith and Hornig. 49 These authors developed a time dependent kinematic model for reconnection occurring along the separator joining two magnetic nulls. They found that singular (since in their model the field near the nulls is ideal) cyclic flows were driven at the nulls by reconnection along a single separator and that as the non-ideal region grows stronger multiple separators form.…”

Section: Discussionmentioning

confidence: 99%

Reconnection at three dimensional magnetic null points: Effect of current sheet asymmetry

Wyper

Jain

2013

Physics of Plasmas

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Use policyThe full-text may be used and/or reproduced, and given to third parties in any format or medium, without prior permission or charge, for personal research or study, educational, or not-for-pro t purposes provided that:• a full bibliographic reference is made to the original source • a link is made to the metadata record in DRO • the full-text is not changed in any way The full-text must not be sold in any format or medium without the formal permission of the copyright holders.Please consult the full DRO policy for further details. Asymmetric current sheets are likely to be prevalent in both astrophysical and laboratory plasmas with complex three dimensional (3D) magnetic topologies. This work presents kinematic analytical models for spine and fan reconnection at a radially symmetric 3D null (i.e., a null where the eigenvalues associated with the fan plane are equal) with asymmetric current sheets. Asymmetric fan reconnection is characterized by an asymmetric reconnection of flux past each spine line and a bulk flow of plasma across the null point. In contrast, asymmetric spine reconnection is characterized by the reconnection of an equal quantity of flux across the fan plane in both directions. The higher modes of spine reconnection also include localized wedges of vortical flux transport in each half of the fan. In this situation, two definitions for reconnection rate become appropriate: a local reconnection rate quantifying how much flux is genuinely reconnected across the fan plane and a global rate associated with the net flux driven across each semi-plane. Through a scaling analysis, it is shown that when the ohmic dissipation in the layer is assumed to be constant, the increase in the local rate bleeds from the global rate as the sheet deformation is increased. Both models suggest that asymmetry in the current sheet dimensions will have a profound effect on the reconnection rate and manner of flux transport in reconnection involving 3D nulls. V C 2013 AIP Publishing LLC.[http://dx

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A Time-Dependent Model for Magnetic Reconnection in the Presence of a Separator

Cited by 20 publications

References 35 publications

Particle acceleration at a reconnecting magnetic separator

Particle acceleration at a reconnecting magnetic separator

Spontaneous reconnection at a separator current layer: 1. Nature of the reconnection

Reconnection at three dimensional magnetic null points: Effect of current sheet asymmetry

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