The scaling of forced collisionless reconnection

We present two-fluid simulations of forced magnetic reconnection with finite electron inertia in a collisionless two-dimensional slab geometry. Reconnection in this system is driven by a spatially localized forcing function that is added to the ion momentum equation inside the computational domain. The resulting forced reconnection process is studied as a function of the temporal and spatial structure of the forcing function, the plasma beta, and strength of the out-of-plane guide magnetic field component, and the electron to ion mass ratio. Consistent with previous results found in unforced, large Delta(') systems, for sufficiently strong forcing the reconnection process is found to become Alfvenic, i.e., the inflow velocity scales roughly like some small fraction of the Alfven speed based on the reconnecting component of the magnetic field just upstream of the dissipation region. The magnitude of this field and thus the rate of reconnection is controlled by the behavior of the forcing function. When the forcing strength is below a certain level, fast reconnection is not observed. (c) 2005 American Institute of Physics.