Three-dimensional magnetic reconnection regimes: A review

Pontin, D. I.

doi:10.1016/j.asr.2010.12.022

Cited by 138 publications

(123 citation statements)

References 89 publications

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“…This effect is also highlighted in Fig. 12 of Pontin (2011), in order to demonstrate the relative complexity of such a model compared with early separator reconnection models. Protons are affected to a greater extent than the electrons by the twisting of magnetic field around the separator since they travel slower than electrons and, therefore, remain in the reconnection region for longer.…”

Section: Discussionmentioning

confidence: 99%

“…However, in 3D, the presence of a localised A&A 574, A7 (2015) non-ideal region (where there exists some component of electric field parallel to the magnetic field) means that this simple "cut and paste" picture of field line reconnection no longer holds; instead magnetic flux is reconnected continually and continuously throughout the non-ideal region (for reviews of 3D magnetic reconnection, see e.g. Priest & Forbes 2000;Birn & Priest 2007;Pontin 2011). Hence, one could view the work presented here as a natural extension of previous work to three dimensions.…”

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: Discussionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Particle acceleration at a reconnecting magnetic separator

Threlfall

Neukirch

Parnell

et al. 2015

A&A

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“…However, we finish by noting that solar nulls are unlikely to be current-free (potential), as is found to be the case in field extrapolations (e.g., Valori et al 2012;Sun et al 2012). Non-potential nulls are more topologically complicated and asymmetric than the potential class (examples of non-potential fieldline geometry can be found in, e.g., Al Hachani & Pontin 2010;Pontin et al 2011;Pontin 2011). Currently, it is unclear to what extent the above results hold in the case of non-potential null points.…”

Section: Discussionmentioning

confidence: 99%

3D Alfvén wave behaviour about proper and improper magnetic null points

Thurgood¹,

McLaughlin²

2013

A&A

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Context. Magnetohydrodynamic (MHD) waves and magnetic null points are both prevalent in many astrophysical plasmas, including the solar atmosphere. Interaction between waves and null points has been implicated as a possible mechanism for localised heating events. Aims. Here we investigate the transient behaviour of the Alfvén wave about fully 3D proper and improper magnetic null points. Methods. We introduce an Alfvén wave into the vicinity of both proper and improper null points by numerically solving the ideal, β = 0 MHD equations using the LARE3D code. A magnetic fieldline and flux-based coordinate system permits the isolation of resulting wave modes and the analysis of their interaction. Results. We find that the Alfvén wave propagates throughout the region and accumulates near the fan-plane, causing current build up. For different values of null point eccentricity, the qualitative behaviour changes only by the imposition of anisotropic pulse dilation, owing to the differing rates at which fieldlines diverge from the spine. For all eccentricities, we find that the fast and Alfvén waves are linearly decoupled. During the driving phase, an independently propagating fast wave is nonlinearly generated owing to the ponderomotive force. Subsequently, no further excitation of fast waves occurs. Conclusions. We find that the key aspects of the theory of Alfvén waves about 2D null points extends intuitively to the fully 3D case; i.e. the wave propagates along fieldlines and thus accumulates at predictable parts of the topology. We also highlight that unlike in the 2D case, in 3D Alfvén-wave pulses are always toroidal, and thus any aspects of 2D Alfvén-wave-null models that are pulse-geometry specific must be reconsidered in 3D.

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“…However, full 3D initial configurations can lead to very different outcomes, as suggested by the few existing kinetic studies (Baumann & Nordlund 2012;Olshevsky et al 2013). Reconnection and particle acceleration at 3D nulls or at quasi separatrix layers (Pontin 2011) deserves further research.…”

Section: Open Questionsmentioning

confidence: 99%

The energetics of relativistic magnetic reconnection: ion-electron repartition and particle distribution hardness

Melzani

Walder

Folini

et al. 2014

A&A

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Collisionless magnetic reconnection is a prime candidate to account for flare-like or steady emission, outflow launching, or plasma heating, in a variety of high-energy astrophysical objects, including ones with relativistic ion-electron plasmas. But the fate of the initial magnetic energy in a reconnection event remains poorly known. What are the amounts assigned to kinetic energy, the ion and electron distribution, and the hardness of the particle distributions? We explored these questions with 2D particle-in-cell simulations of ion-electron plasmas. We find that 45 to 75% of the total initial magnetic energy ends up in kinetic energy, this fraction increasing with the inflow magnetization. Depending on the guide field strength, ions get from 30% to 60% of the total kinetic energy. Particles can be separated into two populations that mix only weakly: (i) particles initially in the current sheet heated by its initial tearing and subsequent contraction of the islands, and (ii) particles from the background plasma that primarily gain energy via the reconnection electric field when passing near the X-point. Particles of (ii) tend to form a power law with an index p = −dlog n(γ)/dlog γ that depends mostly on the inflow Alfvén speed V A and magnetization σ s of species s. For electrons p = 5 to 1.2 for increasing σ e . The highest particle Lorentz factor for ions or electrons increases roughly linearly with time for all the relativistic simulations. This is faster, and the spectra can be harder, than for collisionless shock acceleration. We discuss applications to microquasar and AGN coronae, to extragalactic jets, and to radio lobes. We point out situations where effects, such as Compton drag or pair creation, are important.

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Three-dimensional magnetic reconnection regimes: A review

Cited by 138 publications

References 89 publications

Particle acceleration at a reconnecting magnetic separator

Particle acceleration at a reconnecting magnetic separator

3D Alfvén wave behaviour about proper and improper magnetic null points

The energetics of relativistic magnetic reconnection: ion-electron repartition and particle distribution hardness

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