Power spectrum of the magnetic field in the simulation box as a sequence of time (run A). While the magnetic energy is initially localized on larger scales owing to the coherent toroidal field, a distinct peak at 3.6 Gyr and ~4.4 Gyr is visible. This is due to the generation of fluctuations on smaller scales, in particular through the decreasing separation of the central cores. While these peaks disappear again after the merger, a noticeable amount of power is nevertheless shifted to smaller scales.