Study of Slow-Mode Shock Formation and Particle Acceleration in the Symmetric Magnetic Reconnection Based on Hybrid Simulations

Abstract

The structure of the magnetic reconnection region and the acceleration mechanism of particles as they traverse from upstream into the reconnection exhaust are explored using 2.5D hybrid simulations. The reconnection boundary was analyzed using the Rankine-Hugoniot conditions and the six specific conditions for slow-mode shocks. We observe that the reconnection boundary can be interpreted as a slow-mode shock from as close as ∼9 λ_i (λ_i = ion inertial length) from the X-point. The detection of slow-mode shocks increases with the increasing distance from the X-point and with the increasing ion plasma beta. Additionally, it is observed that if the slow-mode shocks are analyzed by taking artificial satellite cuts at various angles, the detection percentage of slow-mode shocks can decrease to ∼10% for very oblique crossings. The detection percentage of slow-mode shocks is the percentage of points out of the total points studied, where the slow-mode shocks were observed. At the point of incidence into the slow-mode shocks, cold particles get accelerated and they gain energy. However, as we move further from the X-point, a nonclassical picture of slow-mode shocks emerges, where accelerated particles are present in the downstream of the slow-mode shocks, but they are not accelerated in the immediate vicinity of the shock. This crescent-shaped beam population is first accelerated at the slow-mode shock much closer to the X-point, and then it travels to the slow-mode shock downstream region further away from the X-point, gaining energy on the way by reflecting between the two slow-mode shocks.