Collisionless magnetic reconnection with arbitrary guide field

A set of reduced equations governing nonlinear, two-dimensional, two-fluid, collisionless magnetic reconnection with arbitrary guide field is derived. These equations represent an improvement on the existing nonlinear reduced equations generally used to investigate collisionless reconnection, which are only valid in the large guide-field limit. The improved equations are used to calculate the linear growth rate of a strongly unstable, spontaneously reconnecting, plasma instability, as well as the general linear dispersion relation for such an instability.