A magnetic field topology in the vicinity of a single X-nullpoint of RCS with a thickness of 2d along the X-axis (+d and −d from X = 0) and a half width of a along the Z-axis. The particle inflows dragged in at the upper boundary (“x+”) are marked by the blue arrows and the ones at the lower boundary (“x−”) by the red arrows. The x = 0 line represents the current sheet midplane. The green lines show magnetic field lines of B_x and B_z, with the guiding field B_y and reconnecting electric field E_y being perpendicular to the plane of drawing.