Collisionless m=1 reconnection in tokamaks

In high temperature tokamak regimes, the m=1 reconnecting mode is governed by two fluid effects associated with the electron skin-depth de=c/ωpe and the ion sound radius ρs=cs/Ωci. To clarify the early nonlinear dynamics of this mode, numerical simulations of a two fluid model are presented. To simulate physically reasonable parameters in a tokamak geometry, an efficient approach is used in which only a narrow layer surrounding the q=1 surface and m=1 magnetic island must be simulated. In the usual tokamak case ρs≳de, as well as the limit ρs=0, the early nonlinear growth of the mode is faster than exponential due a broadening of the flow layer. This broadening appears to result from tension in the magnetic field lines, which acts to pull the layer open as the island grows.