Particle acceleration in self-driven turbulent reconnection

Abstract

The theoretical prediction that magnetic reconnection spontaneously drives turbulence has been supported by magnetohydrodynamic (MHD) and kinetic simulations. While reconnection with externally driven turbulence is accepted as an effective mechanism for particle acceleration, the acceleration during the reconnection with self-driven turbulence is studied for the first time in this work. By using high-resolution 3D MHD simulations of reconnection with self-generated turbulence, we inject test particles into the reconnection layer to study their acceleration process. We find that the energy gain of the particles takes place when they bounce back and forth between converging turbulent magnetic fields. The particles can be efficiently accelerated in self-driven turbulent reconnection with the energy increase by about 3 orders of magnitude in the range of the box size. The acceleration proceeds when the particle gyroradii become larger than the thickness of the reconnection layer. We find that the acceleration in the direction perpendicular to the local magnetic field dominates over that in the parallel direction. The energy spectrum of accelerated particles is time-dependent with a slope that evolves toward -2.5. Our findings can have important implications for particle acceleration in high-energy astrophysical environments.