Astronomy and Astrophysics – Astrophysics
Scientific paper
Mar 1994
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1994a%26a...283..331c&link_type=abstract
Astronomy and Astrophysics (ISSN 0004-6361), vol. 283, no. 1, p. 331-338
Astronomy and Astrophysics
Astrophysics
13
Current Sheets, Magnetic Field Reconnection, Magnetic Flux, Magnetohydrodynamics, Solar Magnetic Field, Topology, Linear Systems, Plasma Currents, Solar Flares
Scientific paper
We consider cylindrical, X-type magnetic equilibria specified by flux functions of the form rn cos(n theta) with greater than or equal to 2. It is shown that the excess energy associated with arbitrary disturbances comprises three components: a frictional component that can be dissipated by any form of mechanical damping: a topological component Ms that can be dissipated only by a resistive reconnection; and a residual component that is determined by the distribution of normal flux through the outer boundary. We demonstrate that long 'macroscopic' current sheets should naturally develop in compressible plasmas, even for weak finite amplitude disturbances. In particular, for the simplest topological disturbances the current sheet length scales as L2n approximately MS. Next we consider the possibility of fast dynamic reconnection for arbitrary, small amplitude perturbations of the X-point. Although the linear theory allows a formal demonstration of fast energy dissipation for the case n = 2, the dissipation rate is expected to slow for higher n due to the weaker equilibrium field in the vicinity of the neutral point. Simple casual arguments imply 'slow' power law dependences etaP-2/n of the dissipation rate for n greater than 2.
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