Experimental Observation of Energetic Electrons during Magnetic Island Merging

Non-thermal particles have been observed in space as a consequence of magnetic reconnection, but the exact acceleration mechanisms are not well understood. The energization of electrons during magnetic island merging is studied in the Magnetic Reconnection Experiment (MRX). A double-sided electron energy analyzer is developed to simultaneously measure the electron energy distribution in two directions, parallel and anti-parallel to the electron flow. The bias of the selector grid is swept from -30 to 0 V with respect to the floating potential within 1 $\mu s$, comparable to the Alfv\'{e}n time of the typical MRX plasma. Energetic electrons are found inside the magnetic island after island merging is completed. The measured electron tail distribution is well modeled by a high temperature Maxwellian. In the parallel direction, the tail temperature ($\sim $ 28 eV) is found to be up to four times higher than the bulk temperature ($\sim $ 7 eV). In the anti-parallel direction, a negligible tail population is observed. The measured electron energy distribution is discussed in connection with possible electron acceleration mechanisms.