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Solar Particle Acceleration at Reconnecting 3D Null Points  

Adam Stanier   Submitted: 2012-01-24 07:01

Context: The strong electric fields associated with magnetic reconnection insolar flares are a plausible mechanism to accelerate populations of highenergy, non-thermal particles. One such reconnection scenario occurs at a 3Dmagnetic null point, where global plasma flows give rise to strong currents inthe spine axis or fan plane. Aims: To understand the mechanism of chargedparticle energy gain in both the external drift region and the diffusion regionassociated with 3D magnetic reconnection. In doing so we evaluate theefficiency of resistive spine and fan models for particle acceleration, andfind possible observables for each. Method: We use a full orbit test particleapproach to study proton trajectories within electromagnetic fields that areexact solutions to the steady and incompressible magnetohydrodynamic equations.We study single particle trajectories and find energy spectra from manyparticle simulations. The scaling properties of the accelerated particles withrespect to field and plasma parameters is investigated. Results: For fanreconnection, strong non-uniform electric drift streamlines can accelerate thebulk of the test particles. The highest energy gain is for particles that enterthe current sheet, where an increasing 'guide field' stabilises particlesagainst ejection. The energy is only limited by the total electric potentialenergy difference across the fan current sheet. The spine model has both slowexternal electric drift speed and weak energy gain for particles reaching thecurrent sheet. Conclusions: The electromagnetic fields of fan reconnection canaccelerate protons to the high energies observed in solar flares, gaining up to0.1 GeV for anomalous values of resistivity. However, the spine model, whichgave a harder energy spectrum in the ideal case, is not an efficientaccelerator after pressure constraints in the resistive model are included.

Authors: A. Stanier, P. Browning, S. Dalla
Projects: None

Publication Status: Submitted to A&A
Last Modified: 2012-01-24 11:24
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Solar Particle Acceleration at Reconnecting 3D Null Points

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