H. Ji1 - S. C. Prager2
1Princeton Plasma Physics Laboratory Princeton, New Jersey 08543, USA
2Department of Physics, University of Wisconsin Madison, Wisconsin 53706, USA
Abstract
A concise review of observations of the a dynamo effect
in laboratory plasmas is given.
Unlike many astrophysical systems, the laboratory pinch plasmas
are driven magnetically. When the
system is overdriven, the resultant instabilities cause magnetic
and flow fields to fluctuate, and their
correlation induces electromotive forces along the mean magnetic field.
This a-effect drives
mean parallel electric current, which, in turn, modifies
the initial background mean magnetic structure
towards the stable regime. This drive-and-relax cycle,
or the so-called self-organization process,
happens in magnetized plasmas in a time scale much shorter
than resistive diffusion time, thus it is a fast
dynamo process active in a strong magnetic field.
The observed a-effect redistributes
magnetic helicity (a measure of twistedness and knottedness
of magnetic field lines) but conserves its
total value. It can be shown that fast dynamos are natural
consequences of a driven system, where
fluctuations are statistically either not stationary in time
or not homogeneous in space, or both. Implications
to astrophysical phenomena will be discussed. Figs 15, Refs 57.
Full paper: pdf file (493 Kb)
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