Isolating the vortex magnetic action. The lines show the magnetic runs with the MHD instabilities (magneto-elliptic and magneto-rotational) resolved in ideal MHD (P, black solid); unresolved with strong field (Q1, green dot-dot-dot-dashed); most unstable wavelength under-resolved with weak field (R, red dashed); and quenched with resistivity (S, blue dot-dashed). The nonmagnetic 3D hydro run is shown as dotted line in the lower panels. Run Q1 shows that strong magnetic fields have a stabilizing effect on the elliptical instability. Run R shows the magneto-elliptic instability seeming to saturate (at 203 orbits) before the MRI takes over (at 207 orbits). In runs Q2 and S2, the vortex survives until a channel flow develops in the box.