Characteristics of the instability for Re = 2 × 10⁴ and Lu_p = 60. Panels a)–d) are snapshots of, respectively, the azimuthally averaged toroidal field on which the poloidal field lines are superimposed, a meridional cut of and a volume rendering showing surfaces of constant and magnetic field lines at t = 0.33t_ap. Panel b) shows the temporal evolution of the toroidal magnetic energy contained in the first 12 azimuthal wavenumbers.