  The launching process of a magnetically driven outflow from an accretion disk
is investigated in a local, shearing box model which allows a study of the
feedback between accretion and angular momentum loss. The mass-flux instability
found in previous linear analyses of this problem is recovered in a series of
2D (axisymmetric) simulations in the MRI-stable (high magnetic field strength)
regime. At low field strengths that are still sufficient to suppress MRI, the
instability develops on a short radial length scale and saturates at a modest
amplitude. At high field strengths, a long-wavelength "clump" instability of
large amplitude is observed, with growth times of a few orbits. As speculated
before, the unstable connection between disk and outflow may be relevant for
the time dependence observed in jet-producing disks. The success of the
simulations is due in a large part to the implementation of an effective
wave-transmitting upper boundary condition.
