As in Fig. 5 panel f), showing vortical flows in 3D simulation runs with a guide-field of 0.6B_P according to the Q-value at t = 387ω_pe. Panels use perspectives as indicated by axes. In panel a), the dashed lines signify the distance of vortex tubes from the centre of the domain and thus from the centre of the diffusion region. Dashed lines in panel b) are inclined at the calculated value of θ, based on Eq. (6), and show a strong correspondence with the inclination of vortex tubes.