Plasma Physics Seminar ( Phys 769)

Paul Cassak, IREAP

Magnetic Reconnection Onset: A New Mechanism

An open question in Magnetic Reconnection theory is the so-called Onset Problem, which addresses why fast reconnection events in, for example, solar flares and tokamaks begin suddenly after a prolonged quiescent period. Many past models have focused on an instability as the mechanism. In this talk, a new mechanism is proposed, which suggests that the onset of fast reconnection is due to a catastrophic transition from resistive (Sweet-Parker) reconnection - which is very slow - to collisionless reconnection as the resistivity of the system decreases past a critical value. Below this value, the Sweet-Parker configuration ceases to exist. Above this value, both the Sweet-Parker and collisionless reconnection configurations are stable for the same choice of parameters, a condition known as bistability. The configuration that the system takes, then, depends on the history of the system, i.e., there is hysteresis. We present a scaling analysis suggesting the above features and the results of two-fluid numerical simulations. Finally, we discuss the application of this model for reconnection onset in solar flares and sawtooth crashes.