Numerical MHD separator model starting from MHS1; electron a) initial and b) final positions with initial kinetic energy 20 eV and initial pitch angle 45°. c) and d) are the same, but for protons. The colour of each position identifies the (scaled) peak kinetic energy gained during each orbit (see colour bar). For b) and d), the grey orbs indicate the initial position grid, while pink/purple lines indicate interpolated field lines in the fan planes associated with the upper/lower null (indicated by trapezoids) and thick pink/purple lines indicate the corresponding null spines. To aid visualisation, the orb size for each final position has been enhanced in proportion to the final energy. For reference, b_scl = 10 G, l_scl = 1 Mm, and t_scl = 20 s for these orbit simulations.