Driven reconnection in a quadrupole cusp field

Driven magnetic reconnection in a quadrupole cusp field is examined numerically in various collisionality regimes. Quasi-steady-state reconnection rates far in excess of often-quoted limits are observed. As expected, the rate is determined by external boundary conditions and appears to be limited only by computational concerns; thus, in this configuration the slow reconnection is differentiated from the fast one only by changes in the reconnection-layer geometry. Collisional reconnection exhibits the typical extended current layer of the Sweet-Parker model, whereas the collisionless reconnection mediated by kinetic-Alven or whistler waves has the Petschek-type 'X-layer' configuration. The current density at the X point is reduced in the collisionless cases, in qualitative agreement with the results from the Versatile Toroidal Facility experiment