Aspects of three-dimensional magnetic reconnection

The nonlinear behavior of reconnecting modes in three spatial dimensions s3Dd is investigated, on
the basis of a collisionless fluid model in slab geometry, assuming a strong constant guide field in
one direction. Unstable modes in the so-called large D8 regime are considered. Single helicity
modes, i.e., modes with the same orientation with respect to the guide field, depending on all three
spatial coordinates correspond to "oblique" modes with, in general, mixed parity around the
corresponding resonant magnetic surface, giving rise to a nonlinear drift of the magnetic island X
point. The nonlinear coupling of initial perturbations with different helicities introduces additional
helicities that evolve in time in agreement with quasilinear estimates, as long as their amplitudes
remain relatively small. Magnetic field lines become stochastic when islands with different helicities
are present. Basic questions such as the proper definition of the reconnection rate in 3D are
addressed.