Two-fluid theory of collisionless magnetic reconnection

Theoretical studies of collisionless reconnection in the framework of two-fluid theory are presented. In the high-beta case (beta greater than or similar to 1) reconnection is controlled by the whistler mode, leading to decoupling of ions from electrons on scales <c/omega(pi). Though reconnection requires electron inertia, the reconnection rate is independent thereof, controlled only by ion inertia. Reconnection is hence much faster than in the absence of the Hall term. In the opposite limit of small beta the strong axial field suppresses the whistler mode. Hence ions have to follow the electrons in the narrow reconnection layer delta similar to c/omega(pe), forming a macroscopic current sheet which strongly reduces the reconnection rate. Theoretical scaling laws are confirmed by numerical simulations. (C) 1997 American Institute of Physics.