Electrostatic Field Formed by Charge Separation in Magnetic Reconnection with a Guide Field

Abstract The formation of charge separation in antiparallel magnetic reconnection has previously been investigated in S. Hu et al., and the results show that the charge separation arises from the combined effects of the parallel electron flux and the changes in the geometric dimensions of the magnetic flux tube. In this paper, using a 2.5-dimensional particle-in-cell simulation, we characterized the properties of charge separation in guide field magnetic reconnection and conducted a quantitative analysis on how these effects alter the formation of charge separation. In guide field magnetic reconnection, the charge separation develops in the separatrix region: the upper-right and lower-left subregions exhibit positive charge density, whereas the upper-left and lower-right subregions exhibit negative charge density, or conversely, depending on the guide field direction. Under a sufficiently strong guide field, the effect of the geometric dimensions of the flux tube becomes negligible, and the charge separation is dominated by the parallel electron flux. As electrons flow into the vicinity of the X-line along the separatrix in the upper-right and lower-left regions, the parallel electron flux increases. This leads to a negative net flux of electrons, thereby causing positive charge accumulation. Similarly, as electrons flow out of the vicinity of the X-line along the separatrix in the upper-left and lower-right regions, the parallel electron flux decreases, thereby causing negative charge accumulation. Additionally, as the guide field weakens, the effect of the geometric dimensions of the flux tube becomes increasingly significant, and charge separation gradually transforms into the distribution observed in antiparallel magnetic reconnection.