Magnetotail Turbulent Reconnection and Associated Particle Energization

Magnetic reconnection and plasma turbulence are ubiquitous and key processes in the Universe. These two processes are suggested to be intrinsically related: magnetic reconnection can develop turbulence, and, in turn, turbulence can influence or excite magnetic reconnection. In this study, we start with a rare and unique case study, an electron diffusion region (EDR) observed by the Magnetospheric Multiscale mission in the Earth’s magnetotail with significantly enhanced energetic particle fluxes. The EDR is in a region of strong turbulence within which the plasma density is dramatically depleted. This turbulent EDR demonstrates following salient features. (1) Despite the turbulence, the EDR behaves nearly the same as that in 2D quasi-planar reconnection; (2) The observed reconnection electric field and inferred energy transport are exceptionally large. However, the aspect ratio of the EDR (one definition of reconnection rate) is pretty typical. Instead, extraordinarily large-amplitude Hall electric fields appear to enable strong energy transport. Next, we explore the particle energization processes during turbulent reconnection with test particle simulations. Recent studies using test particle simulation compare the particle distributions in a reconnection event with and without turbulence. The results show a separate but sizable population of ions accelerated to significantly higher energies (>80 keV) by the turbulent fields. The extent of the X-line limits the highest acceleration energies, which is consistent with our anticipation that reconnection events with extraordinarily high energization may often have limited cross-tail extension. A similar investigation on electrons shows that electron energization can be dominated by stochastic energization. While low energy electrons experience more parallel energization, and high energy electrons receive more perpendicular energization.