Particle Acceleration in the Outflow Region of Magnetic Reconnection on Solar Flare Loop-tops

Abstract The origin of high-energy particles that generate non-thermal emission at the loop-tops of flare remains unclear. The loop-top regions of flares, which can be reached by outflows generated by magnetic reconnection, are prime candidate regions for the production of high-energy particles. In this work, we study particle acceleration within these regions by combining magnetohydrodynamics and test particle models. We focused on investigating the dynamic characteristics of particles in the two magnetic field configurations with and without a magnetic trap. In one case, the magnetic field contains a downward-concave structure formed by the collision of rapid reconnection outflows with closed magnetic loops, this structure is capable of confining particles for an extended period. Under the influence of the complex electromagnetic field distribution, the particles undergo multiple stochastic acceleration and deceleration processes. Ultimately, a small fraction of particles gain very high energies, while most particles exhibit only modest energy gains. We also observe two distinct particle distribution characteristics: the vast majority of particles are confined within the magnetic trap, with only a small number escaping from this region along open magnetic fields. Notably, the sharp bending of magnetic field lines at the exit of the magnetic trap triggers the aggregation of some particles. In the other case, the magnetic field in the reconnection outflow region does not include the magnetic concave structure, particles are difficult to capture and can quickly leave the outflow area along an open magnetic field. Regardless of the presence or absence of a concave structure, the energy spectra consistently exhibit the power-law distribution.