  We analyze the magnetic evolution of solar active region (AR) NOAA 11476
that, between 9 and 10 May 2012, produced a series of surge-type eruptions
accompanied by GOES X-ray class M flares. Using force-free models of the AR
coronal structure and observations in several wavelengths, in previous works we
studied the detailed evolution of those eruptions, relating them to the
characteristic magnetic topology of the AR and reconstructing the involved
reconnection scheme. We found that the eruptions were due to the ejection of
minifilaments, which were recurrently ejected and reformed at the polarity
inversion line of a bipole that emerged in the middle of the positive main AR
magnetic polarity. The bipole was observed to rotate for several tens of hours
before the events. In this article we analyze, for the full AR and the rotating
bipole, the evolution of a series of magnetic parameters computed using the
Helioseismic and Magnetic Imager (HMI) vector magnetograms. We combine this
analysis with estimations of the injection of magnetic energy and helicity
obtained using the Differential Affine Velocity Estimator for Vector
Magnetograms (DAVE4VM) method that determines, from vector magnetograms, the
affine velocity field constrained by the induction equation. From our results,
we conclude that the bipole rotation was the main driver that provided the
magnetic energy and helicity involved in the minifilament destabilizations and
ejections. The results also suggest that the observed rotation is probably due
to the emergence of a kinked magnetic flux rope with negative writhe helicity.
