Electron magnetohydrodynamic simulations of magnetic island coalescence

The role of electrons in driving magnetic island coalescence in the electron magnetohydrodynamic limit is investigated. In particular, the dependence of the coalescence time t(c)((f)) (defined as the time required for a fixed fraction f of the initial island magnetic flux to reconnect) on the resistivity eta for constant Lundquist number S-lambda (defined in terms of the island wavelength lambda) is studied. Two distinct island coalescence regimes are observed: (1) a "resistive diffusion regime" where t(c)((f)) proportional to t(w)/eta (t(w) equivalent to (lambda (2)/Omega (ci)d(i)(2)), where Omega (ci) is the ion cyclotron frequency, and d(i) is the ion inertial length), and (2) an "electron driven regime" where t(c)((f)) proportional to t(w). Defining the "ion Lundquist number," S-i equivalent to S(lambda)d(i)/lambda, the resistive diffusion regime is observed when S-i less than or similar to 50, while the electron driven regime is observed when S-i greater than or similar to 50. In the electron driven regime, the coalescence time is insensitive to S-i over the range 50 less than or similar to S-i less than or similar to 250. (C) 2001 American Institute of Physics.