Kinetic simulations of magnetic reconnection in presence of a background   O+ population
  Particle-in-Cell simulations of magnetic reconnection with an H+ current sheet and a mixed background plasma of H+ and O+ ions are completed using physical mass ratios. Four main results are shown. First, the O+ presence slightly decreases the reconnection rate and the magnetic reconnection evolution depends mainly on the lighter H+ ion species in the presented simulations. Second, the Hall magnetic field is characterized by a two-scale structure in presence of O+ ions: it reaches sharp peak values in a small area in proximity of the neutral line, and then decreases slowly over a large region. Third, the two background species initially separate in the outflow region because H+ and O+ ions are accelerated by different mechanisms occurring on different time scales and with different strengths. Fourth, the effect of a guide field on the O+ dynamics is studied: the O+ presence does not change the reconnected flux and all the characteristic features of guide field magnetic reconnection are still present. Moreover, the guide field introduces an O+ circulation pattern between separatrices that enhances high O+ density areas and depletes low O+ density regions in proximity of the reconnection fronts. The importance and the validity of these results are finally discussed. 
Stefano Markidis, Giovanni Lapenta, Lapo Bettarini, Martin V. Goldman,   David Newman, Laila Andersson
physics.plasm-ph