Abstract:

A plasma flow near a stagnation point, which may be produced by a local squeezing in one direction with outflow on both sides of a central channel, convects a magnetic field towards the inner layer, while enhancement of the initial magnetic energy and formation of a current sheet with intense Joule dissipation rates take place when the magnetic Reynolds number is large. In systems with no magnetic flux injection, starting from a generic initial magnetic field and after a transient in which amplification followed by annihilation of the odd component occurs, a large even magnetic remnant concentrated in a thin slab is formed in a few hydrodynamic times. If the pressure gradient that drives the motion is switched off, the magnetic field extinguishes at a much slower pace than the corresponding buildup process. When there is continuous magnetic flux injection, the even component of the magnetic field, in general, becomes dominant over the odd part after some number of hydrodynamic times. For astrophysical plasmas the significance of the mechanism considered here is that i) fast dissipation of magnetic energy does not invoke anomalous resistivity, and ii) neutral sublayers where change of sign of magnetic field occurs may vanish during the current sheet evolution, so that steady-state configurations prone to processes of reconnection or tearing instabilities do not develop. © 1992 IEEE