Particle acceleration in a transient magnetic reconnection event

Gordovskyy, Mykola; Browning, Philippa; Vekstein, G.

doi:10.1051/0004-6361/200913569

Cited by 54 publications

(36 citation statements)

References 55 publications

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“…Unfortunately the timestep required to resolve the evolution of the test particle is too small to be practical (for the magnetic field strengths typical of the corona). A common alternative is to use the guiding centre approximation when computing particle orbits (see for example Gordovskyy et al 2010;Threlfall et al 2016;Borissov et al 2016). In this approach the position of the test particle is averaged over a gyration period (this averaged position is referred We present only the subset of the MHD simulation domain which is within the test particle computational box.…”

Section: Governing Equations For Test Particle Evolutionmentioning

confidence: 99%

Particle acceleration with anomalous pitch angle scattering in 2D magnetohydrodynamic reconnection simulations

Borissov

Kontar

Threlfall

et al. 2017

A&A

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The conversion of magnetic energy into other forms (such as plasma heating, bulk plasma flows, and non-thermal particles) during solar flares is one of the outstanding open problems in solar physics. It is generally accepted that magnetic reconnection plays a crucial role in these conversion processes. In order to achieve the rapid energy release required in solar flares, an anomalous resistivity, which is orders of magnitude higher than the Spitzer resistivity, is often used in magnetohydrodynamic (MHD) simulations of reconnection in the corona. The origin of Spitzer resistivity is based on Coulomb scattering, which becomes negligible at the high energies achieved by accelerated particles. As a result, simulations of particle acceleration in reconnection events are often performed in the absence of any interaction between accelerated particles and any background plasma. This need not be the case for scattering associated with anomalous resistivity caused by turbulence within solar flares, as the higher resistivity implies an elevated scattering rate. We present results of test particle calculations, with and without pitch angle scattering, subject to fields derived from MHD simulations of two-dimensional (2D) X-point reconnection. Scattering rates proportional to the ratio of the anomalous resistivity to the local Spitzer resistivity, as well as at fixed values, are considered. Pitch angle scattering, which is independent of the anomalous resistivity, causes higher maximum energies in comparison to those obtained without scattering. Scattering rates which are dependent on the local anomalous resistivity tend to produce fewer highly energised particles due to weaker scattering in the separatrices, even though scattering in the current sheet may be stronger when compared to resistivity-independent scattering. Strong scattering also causes an increase in the number of particles exiting the computational box in the reconnection outflow region, as opposed to along the separatrices as is the case in the absence of scattering.

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Section: Governing Equations For Test Particle Evolutionmentioning

confidence: 99%

Particle acceleration with anomalous pitch angle scattering in 2D magnetohydrodynamic reconnection simulations

Borissov

Kontar

Threlfall

et al. 2017

A&A

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“…Electron distribution functions are calculated using the GCA test-particle code based on first-order guiding-centre approxima- tion (Gordovskyy et al 2010;Gordovskyy & Browning 2011):…”

Section: Test-particle Trajectories and Synthetic Hard X-ray Bremsstrmentioning

confidence: 99%

Thermal and non-thermal emission from reconnecting twisted coronal loops

Pinto

Gordovskyy

Browning

et al. 2016

A&A

Self Cite

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Context. Twisted magnetic fields should be ubiquitous in the solar corona, particularly in flare-producing active regions where the magnetic fields are strongly non-potential. The magnetic energy contained in such twisted fields can be released during solar flares and other explosive phenomena. It has been shown recently that reconnection in helical magnetic coronal loops results in plasma heating and particle acceleration distributed within a large volume, including the lower coronal and chromospheric sections of the loops. Hence, the magnetic reconnection and particle acceleration scenario involving magnetic helicity can be a viable alternative to the standard flare model, where particles are accelerated only in a small volume located in the upper corona. Aims. The key goal of this study is to investigate the links and observational signatures of plasma heating and particle acceleration in kink-unstable twisted coronal loops. Methods. We use a combination of MHD simulations and test-particle methods. These simulations describe the development of kink instability and magnetic reconnection in twisted coronal loops using resistive compressible MHD, and incorporate atmospheric stratification and large-scale loop curvature. The resulting distributions of hot plasma let us estimate thermal X-ray emission intensities. The electric and magnetic fields obtained are used to calculate electron trajectories using the guiding-centre approximation. These trajectories combined with the MHD plasma density distributions let us deduce synthetic hard X-ray bremsstrahlung intensities. Results. Our simulations emphasise that the geometry of the emission patterns produced by hot plasma in flaring twisted coronal loops can differ from the actual geometry of the underlying magnetic fields. In particular, the twist angles revealed by the emission threads (soft X-ray thermal emission; SXR) are consistently lower than the field-line twist present at the onset of the kink-instability. Hard X-ray (HXR) emission due to the interaction of energetic electrons with the stratified background are concentrated at the loop foot-points in these simulations, even though the electrons are accelerated everywhere within the coronal volume of the loop. The maximum of HXR emission consistently precedes that of SXR emission, with the HXR light-curve being approximately proportional to the temporal derivative of the SXR light-curve.

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“…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. The main features of an isolated 3D magnetic null point are the spine axis and fan plane.…”

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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Particle acceleration in a transient magnetic reconnection event

Cited by 54 publications

References 55 publications

Particle acceleration with anomalous pitch angle scattering in 2D magnetohydrodynamic reconnection simulations

Particle acceleration with anomalous pitch angle scattering in 2D magnetohydrodynamic reconnection simulations

Thermal and non-thermal emission from reconnecting twisted coronal loops

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

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