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Magnetic reconnection can convert magnetic energy into kinetic energy ofnon-thermal electron beams. Those accelerated electrons can, in turn, causeradio emission in astrophysical plasma environments such as solar flares viamicro-instabilities. The properties of the electron velocity distributionfunctions (EVDFs) of those non-thermal beams generated by reconnection are,however, still not well understood. In particular properties that are necessaryconditions for some relevant micro-instabilities. We aim at characterizing theEVDFs generated in 3D magnetic reconnection by means of fully kineticparticle-in-cell (PIC) code simulations. In particular, our goal is to identifythe possible sources of free energy offered by the generated EVDFs and theirdependence on the strength of the guide field. By applying a machine learningalgorithm on the EVDFs, we find that: (1) electron beams with positivegradients in their 1D parallel (to the local magnetic field direction) velocitydistribution functions are generated in both diffusion region and separatrices.(2) Electron beams with positive gradients in their perpendicular (to the localmagnetic field direction) velocity distribution functions are observed in thediffusion region and outflow region near the reconnection midplane. Inparticular, perpendicular crescent-shaped EVDFs (in the perpendicular velocityspace) are mainly observed in the diffusion region. (3) As the guide fieldstrength increases, the number of locations with EVDFs featuring aperpendicular source of free energy significantly decreases. The formation ofnon-thermal electron beams in the field-aligned direction is mainly due tomagnetized and adiabatic electrons, while in the direction perpendicular to thelocal magnetic field it is attributed to unmagnetized electrons.

Nonthermal electron velocity distribution functions due to 3D kinetic magnetic reconnection for solar coronal plasma conditions