Particle trajectories and acceleration during 3D fan reconnection

¹ School of Physics and Astronomy, University of Manchester, Manchester M13 9PL, UK

² Centre for Astrophysics, University of Central Lancashire, Preston PR1 2HE, UK e-mail: sdalla@uclan.ac.uk

Received: 12 March 2008
Accepted: 6 September 2008

Abstract

Context. The primary energy release in solar flares is almost certainly due to magnetic reconnection, making this a strong candidate as a mechanism for particle acceleration. While particle acceleration in 2D geometries has been widely studied, investigations in 3D are a recent development. Two main classes of reconnection regimes at a 3D magnetic null point have been identified: fan and spine reconnection

Aims. Here we investigate particle trajectories and acceleration during reconnection at a 3D null point, using a test particle numerical code, and compare the efficiency of the fan and spine regimes in generating an energetic particle population.

Methods. We calculated the time evolution of the energy spectra. We discuss the geometry of particle escape from the two configurations and characterise the trapped and escaped populations.

Results. We find that fan reconnection is less efficent than spine reconnection in providing seed particles to the region of strong electric field where acceleration is possible. The establishment of a steady-state spectrum requires approximately double the time in fan reconnection. The steady-state energy spectrum at intermediate energies (protons 1 keV to 0.1 MeV) is comparable in the fan and spine regimes. While in spine reconnection particle escape takes place in two symmetric jets along the spine, in fan reconnection no jets are produced and particles escape in the fan plane, in a ribbon-like structure.