In:
Journal of Plasma Physics, Cambridge University Press (CUP), Vol. 46, No. 1 ( 1991-08), p. 179-199
Kurzfassung:
The dissipation of relative magnetic helicity due to the presence of a resistive reconnection region is considered. We show that when the reconnection region has a vanishing cross-section, helicity is conserved, in agreement with previous studies. It is also shown that in two-dimensional systems reconnection can produce highly twisted reconnected flux tubes. Reconnection at a high magnetic Reynolds number generally conserves helicity to a good approximation. However, reconnection with a small Reynolds number can produce significant dissipation of helicity. We prove that helicity dissipation in two-dimensional configurations is associated with the retention of some of the inflowing magnetic flux by the reconnection region, v r . When the reconnection site is a simple Ohmic conductor, all of the magnetic field parallel to the reconnection line that is swept into v r is retained. (In contrast, the inflowing magnetic field perpendicular to the line is annihilated.) We are able to relate the amount of helicity dissipation to the retained flux. A physical interpretation of helicity dissipation is developed by considering the diffusion of magnetic field lines through v r . When compared with helicity-conserving reconnection, the two halves of a reconnected flux sheet appear to have slipped relative to each other parallel to the reconnection line. This provides a useful method by which the reconnected field geometry can be constructed: the incoming flux sheets are ‘cut’ where they encounter v r , allowed to slip relative to each other, and then ‘pasted’ together to form the reconnected flux sheets. This simple model yields estimates for helicity dissipation and the flux retained by v r in terms of the amount of slippage. These estimates are in agreement with those expected from the governing laws.
Materialart:
Online-Ressource
ISSN:
0022-3778
,
1469-7807
DOI:
10.1017/S0022377800016019
Sprache:
Englisch
Verlag:
Cambridge University Press (CUP)
Publikationsdatum:
1991
ZDB Id:
2004297-8
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