We present MHD simulations in both 2D axisymmet-ric and 3D spherical geometries of the evolution of a twisted magnetic flux rope emerging into the low-β corona previously occupied by a potential arcade field. These simulations show two distinct stages of the evolution. The earlier evolution is quasistatic during which if the flux emergence is stopped, the flux rope settles to a neighboring equilibrium with stored free magnetic energy. Loss of equilibrium and eruption of the flux rope are found for both a 2D axisymmetric flux rope and a 3D line-tied flux rope, when too much twisted flux has been transported into the corona.
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