Three-dimensional magnetic reconnection in astrophysical plasmas -: Kinetic approach

Reconnection is the most efficient way to release the energy accumulated in the tense astrophysical magnetoplasmas. As such it is a basic paradigm of energy conversion in the universe. Astrophysical reconnection is supposed to heat plasmas to high temperatures, it drives fast flows, winds and jets, it accelerates particles and leads to structure formation. Reconnection can take place only after a local breakdown of the plasma ideality, enabling a change of the magnetic connection between plasma elements. After Giovanelli first suggested magnetoplasma discharges in 1946, reconnection has usually been identified with vanishing magnetic field regions. However, for the last ten years a discussion has been going on about the structure of 3 D reconnection, e.g., whether in 3 D it is possible also without magnetic nulls or not. We first shortly review the relevant magnetostatic and kinematic fluid theory results to argue than that a kinetic approach is necessary to reveal the generic three-dimensional structure and dynamics of reconnection in collisionless astrophysical plasmas. We present results about the 3 D structure of kinetic reconnection in initially antiparallel magnetic fields. They were obtained by selfconsistently considering ion and electron inertia as well as dissipative wave-particle resonances. In this approach reconnection is a natural consequence of the instability of thin current sheets. We present the results of a nonlocal linear dispersion theory and describe the nonlinear evolution of the instability using numerical particle code simulations. The decay of thin current sheets directly leads to a configurational instability and three-dimensional dynamic reconnection. We report the resulting generic magnetic field structure. It contains pairs of magnetic nulls, connected by separating magnetic flux surfaces through which the plasma flows and along which reconnection induces large parallel electric fields. Our results are illustrated by virtual reality views and movies, both stored on the attached CD-ROM and also being available from the Internet.