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tokens: open field lines. The plots of null height (Figure 4 (a), red line) and free magnetic energy (Figure 4 (b), red line) also indicate that the system has almost relaxed back to its equilibrium state. The free magnetic energy (b) sharply drops as soon as the photospheric driving stops. This is because energy is being propagated out of the open top boundary along the jet spire, but is no longer being injected through the lower boundary. The null height (a) continues to increase until around t = 70, showing that the jet dome has continued to expand. The decrease in null height after this point is more rapid than that in PAD09 (black line) as there is no longer photospheric driving injecting energy and twist into the field. We now compare our PAD10 simulation with that of Pariat et al. ( 2010 ), as well as PAD09 and PAD09R. In Pariat et al. ( 2009 ) they see a peak and sudden drop in free magnetic energy when the eruption occurs after kinking breaks the symmetry of the model. In Pariat et al. ( 2010 ), the model is initially set up to be non-symmetric, with the background magnetic field inclined at 10° to the vertical. They continue to rotate the positive magnetic polarity after the first eruption, resulting in a series of eruptive events, hence a series of peaks and drops in free energy. The free magnetic energy in our model can be seen in Figure 4 (b) (blue line). We do see a series of peaks in our model, but they are not sharply defined, as there is not as rapid a decrease in energy after each peak. Again, this is due to the quasi-static nature of the magnetofrictional method. We cannot accurately follow the dynamics of an eruption, so the result is that not as much energy and twist is released before it starts building up again due to the photospheric driving. The first peak occurs at a similar time to that of our PAD09 simulation. The peak free magnetic energy built up before the first release is 1.45 × 10 25 erg and 1.29 × 10 25 erg for the PAD09 and PAD10 simulations, respectively. The energy buildup is greater in PAD09, as changes in connectivity do not occur until after the onset of the kink and the breaking of the structure’s symmetry. In PAD10, the symmetry is already broken in the initial setup, so changes in connectivity can occur as soon as the simulation begins and magnetic energy can already be released. Figure 5 (a) shows in the xz -plane at y = 9 Mm for PAD09 (left), PAD10 (center), and PAD09R (right). An animated version of these panels is available online. In PAD09 and PAD09R, current is initially all contained within the twisted dome of the jet and along the narrow, vertical jet spire, indicating that no twist has been released and almost all non-potentiality is contained within the dome. After the onset of the kink, the symmetry of the system is broken and we see a broader jet spire, as in Figure 5 (a). In PAD10, the spire broadens more rapidly, as connectivity changes occur with background magnetic field right from the start