Comparative Analysis of Electron Acceleration Mechanisms During Magnetotail Reconnection

Magnetic reconnection is a critical process in astrophysical environments responsible for converting magnetic energy into plasma kinetic energy, often manifested as particle acceleration. This study aims to determine the dominant mechanism responsible for electrons acceleration during magnetic reconnection by investigating the average properties of energetic electron acceleration in the magnetotail reconnection region, focusing on three key mechanisms: Fermi acceleration, Betatron acceleration, and acceleration by parallel electric field. Using Magnetospheric MultiScale (MMS) observations of seven magnetic reconnection events during 2015-2017 in the magnetotail, we evaluate and compare the reconnection rate, power density, and the electron acceleration rate associated with each mechanism. The analysis reveals that Betatron acceleration contributes most significantly, exhibiting higher average acceleration rates than the other two mechanisms while acceleration due to parallel electric fields contributes considerably less. Betatron acceleration has an average relative contribution of 76.6%, compared with 16.9% for the Fermi mechanism and 6.5% for the parallel electric field mechanism. Furthermore, reconnection events with enhanced particle acceleration rate generally coincide with enhanced power density, indicating that faster reconnection facilitates stronger and more efficient energy transfer to electrons. The event with high acceleration rates also coincide with relatively high reconnection rates (0.05 and 0.07). These results suggest that Betatron-type acceleration plays a dominant role in energetic electrons acceleration. The findings provide observational support for the mechanism responsible for electron acceleration and contribute to a better understanding of energy conversion and particle acceleration in collisionless plasmas.