Turbulent magnetic reconnection in 2D and 3D
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abstract
Magnetic field embedded in a perfectly conducting fluid preserves its
topology for all time. Although ionized astrophysical objects, like stars and
galactic disks, are almost perfectly conducting, they show indications of
changes in topology, `magnetic reconnection', on dynamical time scales.
Reconnection can be observed directly in the solar corona, but can also be
inferred from the existence of large scale dynamo activity inside stellar
interiors. Solar flares and gamma ray busts are usually associated with
magnetic reconnection. Previous work has concentrated on showing how
reconnection can be rapid in plasmas with very small collision rates. Here we
present numerical evidence, based on three dimensional simulations, that
reconnection in a turbulent fluid occurs at a speed comparable to the rms
velocity of the turbulence, regardless of the value of the resistivity. In
particular, this is true for turbulent pressures much weaker than the magnetic
field pressure so that the magnetic field lines are only slightly bent by the
turbulence. These results are consistent with the proposal by Lazarian and
Vishniac (1999) that reconnection is controlled by the stochastic diffusion of
magnetic field lines, which produces a broad outflow of plasma from the
reconnection zone. This work implies that reconnection in a turbulent fluid
typically takes place in approximately a single eddy turnover time, with broad
implications for dynamo activity and particle acceleration throughout the
universe. In contrast, the reconnection in 2D configurations in the presence of
turbulence depends on resistivity, i.e. is slow.
