Comparisons of electron acceleration efficiency among different structures during magnetic reconnection: a Cluster multicase study

摘要

Magnetic reconnection has long been believed to be an efficient engine forenergetic electrons production. Four different structures have been proposedfor electrons being energized: flux pileup region, density cavitylocated around the separatrix, magnetic island and thin current sheet. Inthis paper, we compare the electron acceleration efficiency among thesestructures based on 12 magnetotail reconnection events observed by theCluster spacecraft in 2001–2006. We used the flux ratio between theenergetic electrons (> 50 keV) and lower energy electrons(< 26 keV) to quantify the electron acceleration efficiency. We donot find any specific sequence in which electrons are accelerated withinthese structures, though the flux pileup region, magnetic island and thincurrent sheet have higher probabilities to reach the maximum efficiencyamong the four structures than the density cavity. However, the mostefficient electron energization usually occurs outside these structures. Wesuggest that other structures may also play important roles in energizingelectrons. Our results could provide important constraints for the furthermodeling of electron acceleration during magnetic reconnection.