Electric-drift generated trajectories and particle acceleration in collisionless magnetic reconnection

Vekstein, G.; Browning, Philippa

doi:10.1063/1.872555

Cited by 30 publications

(43 citation statements)

References 6 publications

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“…their gyro-radii are much smaller than the field's scale length), their energies are approximately the same as for electrons. The small noticeable difference is most likely due to the difference in the initial thermal velocities, which are comparable to the drift velocity u E for protons and much higher than u E for electrons (see discussion in Vekstein & Browning 1997;Browning & Vekstein 2001).…”

Section: Particle Energy Spectramentioning

confidence: 99%

Particle acceleration in a transient magnetic reconnection event

Gordovskyy¹,

Browning²,

Vekstein³

2010

A&A

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Context. In the present paper, we investigate particle acceleration by direct electric field in solar flares. Aims. Proton and electron kinetics are considered based on MHD simulations of magnetic reconnection, with the aim of determining the properties of accelerated particles in a time-dependent reconnecting event model. Methods. At first, we considered several two-dimensional numerical models of forced reconnection in the initially force-free Harris current sheet. The electric and magnetic fields from these models were then used to study proton and electron motion with the guiding centre, test particle approach. Results. It is shown that protons and electrons can be accelerated to very high energies up to tens of MeV in the present model. The energy spectra for both particle species are combinations of exponential and rather hard power-law shapes. Also, protons and electrons are ejected from the CS in different directions.

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Section: Particle Energy Spectramentioning

confidence: 99%

Particle acceleration in a transient magnetic reconnection event

Gordovskyy¹,

Browning²,

Vekstein³

2010

A&A

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“…Moreover, the electric drift u E = E × B/B 2 may also cause particle acceleration (e.g, Vekstein & Browning 1997;Northrop 1963). When the particles move away from the null point, the continuous change of the magnetic and electric field will lead to the non-uniformity of the electric drift speed.…”

Section: How Can a Convective Electric Field Accelerate Particles?mentioning

confidence: 99%

Is the 3-D magnetic null point with a convective electric field an efficient particle accelerator?

Guo

Büchner

Otto

et al. 2010

A&A

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Aims. We study the particle acceleration at a magnetic null point in the solar corona, considering self-consistent magnetic fields, plasma flows and the corresponding convective electric fields. Methods. We calculate the electromagnetic fields by 3-D magnetohydrodynamic (MHD) simulations and expose charged particles to these fields within a full-orbit relativistic test-particle approach. In the 3-D MHD simulation part, the initial magnetic field configuration is set to be a potential field obtained by extrapolation from an analytic quadrupolar photospheric magnetic field with a typically observed magnitude. The configuration is chosen so that the resulting coronal magnetic field contains a null. Driven by photospheric plasma motion, the MHD simulation reveals the coronal plasma motion and the self-consistent electric and magnetic fields. In a subsequent test particle experiment the particle energies and orbits (determined by the forces exerted by the convective electric field and the magnetic field around the null) are calculated in time.Results. Test particle calculations show that protons can be accelerated up to 30 keV near the null if the local plasma flow velocity is of the order of 1000 km s −1 (in solar active regions). The final parallel velocity is much higher than the perpendicular velocity so that accelerated particles escape from the null along the magnetic field lines. Stronger convection electric field during big flare explosions can accelerate protons up to 2 MeV and electrons to 3 keV. Higher initial velocities can help most protons to be strongly accelerated, but a few protons also run the risk to be decelerated. Conclusions. Through its convective electric field and due to magnetic nonuniform drifts and de-magnetization process, the 3-D null can act as an effective accelerator for protons but not for electrons. Protons are more easily de-magnetized and accelerated than electrons because of their larger Larmor radii. Notice that macroscopic MHD simulations are blind to microscopic magnetic structures where more non-adiabatic processes might be taking place. In the real solar corona, we expect that particles could have a higher probability to experience a de-magnetization process and get accelerated. To trigger a significant acceleration of electrons and even higher energetic protons, however, the existence of a resistive electric field mainly parallel to the magnetic field is required. A physically reasonable resistivity model included in resistive MHD simulations is direly needed for the further investigations of electron acceleration by parallel electric fields.

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“…12 Detection of magnetic null points in numerical experiments requires both a fast and an accurate method. 13 The first step in understanding charged particle motion in the vicinity of null points was the development of twodimensional (2D) models and using a test particle approach, on either prescribed electromagnetic fields, i.e., X-type null point configuration 14,15 or fields calculated from the snapshots of magnetohydrodynamics (MHD) simulations. 16 In recent times, three dimensional (3D) models have also been studied in this context.…”

Section: Introductionmentioning

confidence: 99%

Dynamics of charged particle motion in the vicinity of three dimensional magnetic null points: Energization and chaos

Gascoyne

2015

Physics of Plasmas

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Using a full orbit test particle approach, we analyse the motion of a single proton in the vicinity of magnetic null point configurations which are solutions to the kinematic, steady state, resistive magnetohydrodynamics equations. We consider two magnetic configurations, namely, the sheared and torsional spine reconnection regimes [E. R. Priest and D. I. Pontin, Phys. Plasmas 16, 122101 (2009); P. Wyper and R. Jain, Phys. Plasmas 17, 092902 (2010)]; each produce an associated electric field and thus the possibility of accelerating charged particles to high energy levels, i.e., > MeV, as observed in solar flares [R. P. Lin, Space Sci. Rev. 124, 233 (2006)]. The particle's energy gain is strongly dependent on the location of injection and is characterised by the angle of approach b, with optimum angle of approach b opt as the value of b which produces the maximum energy gain. We examine the topological features of each regime and analyse the effect on the energy gain of the proton. We also calculate the complete Lyapunov spectrum for the considered dynamical systems in order to correctly quantify the chaotic nature of the particle orbits. We find that the sheared model is a good candidate for the acceleration of particles, and for increased shear, we expect a larger population to be accelerated to higher energy levels. In the strong electric field regime (E 0 ¼ 1500 V/m), the torsional model produces chaotic particle orbits quantified by the calculation of multiple positive Lyapunov exponents in the spectrum, whereas the sheared model produces chaotic orbits only in the neighbourhood of the null point. V C 2015 AIP Publishing LLC.

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Electric-drift generated trajectories and particle acceleration in collisionless magnetic reconnection

Cited by 30 publications

References 6 publications

Particle acceleration in a transient magnetic reconnection event

Particle acceleration in a transient magnetic reconnection event

Is the 3-D magnetic null point with a convective electric field an efficient particle accelerator?

Dynamics of charged particle motion in the vicinity of three dimensional magnetic null points: Energization and chaos

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