Fluctuating electric field particle acceleration at a magnetic field null point

Abstract

Release of stored magnetic energy via particle acceleration is a characteristic feature of astrophysical plasmas. Magnetic reconnection is one of the primary candidate mechanisms for releasing non-potential energy from magnetized plasmas. A collisionless magnetic reconnection scenario could provide both the energy release mechanism and the particle accelerator in flares. We studied particle acceleration consequences from fluctuating (in-time) electric fields superposed on an X-type magnetic field in collisionless hot solar plasma. This system is chosen to mimic generic features of dynamic reconnection, or the reconnective dissipation of a linear disturbance. Time evolution of thermal particle distributions are obtained by numerically integrating particle orbits. A range of frequencies of the electric field is used, representing a turbulent range of waves. Depending on the frequency and amplitude of the electric field, electrons and ions are accelerated to different degrees and often have energy distributions of bimodal form. Protons are accelerated to gamma-ray producing energies and electrons to and above hard X-ray producing energies in timescales of less than 1 second. The acceleration mechanism could be applicable to all collisionless plasmas