A Systematic Examination of Particle Motion in a Collapsing Magnetic Trap Model for Solar Flares

TL;DR

This study systematically investigates particle energization in collapsing magnetic traps during solar flares, revealing how initial conditions and trap symmetry influence energy gains and acceleration mechanisms.

Contribution

It provides the first detailed comparison of symmetric and asymmetric trap models, highlighting differences in energy gain and particle escape behaviors.

Findings

Particles can gain up to 50 times their initial energy.

Highest energy gains occur for particles starting in weak field regions with pitch angles around 90°.

Symmetric traps yield larger energy gains and fewer escapes than asymmetric traps.

Abstract

Context. It has been suggested that collapsing magnetic traps may contribute to accelerating particles to high energies during solar flares. Aims. We present a detailed investigation of the energization processes of particles in collapsing magnetic traps, using a specific model. We also compare for the first time the energization processes in a symmetric and an asymmetric trap model. Methods. Particle orbits are calculated using guiding centre theory. We systematically investigate the dependence of the energization process on initial position, initial energy and initial pitch angle. Results. We find that in our symmetric trap model particles can gain up to about 50 times their initial energy, but that for most initial conditions the energy gain is more moderate. Particles with an initial position in the weak field region of the collapsing trap and with pitch angles around 90 degrees achieve the highest energy gain, with betatron acceleration of the perpendicular energy the dominant energization mechanism. For particles with smaller initial pitch angle, but still outside the loss cone, we find the possibility of a significant increase in parallel energy. This increase in parallel energy can be attributed to the curvature term in the parallel equation of motion and the associated energy gain happens in the center of the trap where the field line curvature has its maximum. We find qualitatively similar results for the asymmetric trap model, but with smaller energy gains and a larger number of particles escaping from the trap.