Paul Cassak
University of Maryland
Catastrophe Model for the Onset of Fast Magnetic Reconnection
The mechanism triggering the onset of fast magnetic reconnection, the driver of solar eruptions and fusion device disruptions, has long been elusive. We have found that for a wide range of resistivities, both the collisional ("Sweet-Parker", exceedingly slow) and collisionless ("Hall", fast) reconnection solutions are independently valid for identical values of the resistivity, a condition known as bistability. However, when the dissipation region becomes thinner than the ion skin depth, the Sweet-Parker solution ceases to exist (i.e., there is a bifurcation), and a catastrophic transition to Hall reconnection ensues - increasing the rate of reconnection by a factor of 105. Since the current sheet naturally thins during the reconnection process as stronger magnetic fields are convected into the dissipation region, this process is entirely spontaneous. In this talk, we will review the Sweet-Parker and Hall reconnection models, present theory and simulation results on the resistivity dependence of magnetic reconnection, and discuss the potential impact of this onset mechanism on solar flares.