Magnetic reconnection simulation using the 2.5 D electromagnetic direct implicit code 'Avanti'

Collisionless reconnection of magnetic field lines depends upon electron inertia effects and details of the electron and ion distribution functions, thus requiring a kinetic description of both. Though traditional explicit particle-in-cell (PIC) techniques provide this description in principle, they are severly limited in parameters by time step constraints. This parameter regime has been expanded by using the recently constructed 2.5 D electromagnetic code AVANTI in this work. The code runs stably with arbitrarily large δt and is quite robust with respect to large fluctuations occurring due to small numbers of particles per cell. We have found several qualitatively new features. The reconnection process is found to ocur indistinct stages: 1)early spontaneous reconnection fed by the free energy of an initial anisotropy in the electron component, 2) coalescence of the resulting small-scale filaments of electron current, accompanied by electron jetting, and 3) oscillatory flow of electrons through the magnetic X-point, superposed on continuing nonlinear growth of ion-mediated reconnection. The time evolution of stage 3) is strongly dependent on M-i/m-e. (author). 12 refs.; 6 figs