  The Accretion-Ejection Instability (AEI) described by Tagger & Pellat (1999)
is explored numerically using a global 2d model of the inner region of a
magnetised accretion disk. The disk is initially currentless but threaded by a
vertical magnetic field created by external currents, and frozen in the flow.
In agreement with the theory a spiral instability, similar in many ways to
those observed in self-gravitating disks, develops when the magnetic field is,
within a factor of a few, at equipartition with the disk thermal pressure.
Perturbations in the flow build up currents and create a perturbed magnetic
field within the disk. The present non-linear simulations give good evidence
that such an instability can occur in the inner region of accretion disks, and
generate accretion of gas and vertical magnetic flux toward the central object,
if the equilibrium radial profiles of density and magnetic flux exceed a
critical threshold.
