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Astron. Astrophys. 318, 621-630 (1997)


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The form of ideal current layers and kink instability in line-tied coronal loops

H. Baty

Observatoire Astronomique, 11 Rue de l'Université, F-67000 Strasbourg, France

Received 28 March 1996 / Accepted 3 July 1996

Abstract

We have investigated the characteristics of the current concentration which develops when an unstable line-tied coronal loop is driven by an ideal kink instability towards a secondary bifurcated magnetohydrodynamic (MHD) equilibrium. Using fully three dimensional MHD simulations in cylindrical geometry, the main results indicate an algebraic linear-like dependence of the thickness and amplitude of the current concentration on the aspect ratio of the loop. A simple model is proposed, which interprets this scaling in terms of the axial field line bending effect due to the line-tying constraints in the kinked configuration. Indeed, a curvature force term arises and prevents the formation of a current sheet, which is known to develop in un-tied configuration. For the typical parameters of observed loops, the thickness of the current layer is approximately two or three orders of magnitude smaller than the length scale of the initial equilibrium. Finally, we discuss the subsequent current dissipation and the efficiency with which such a mechanism can heat the corona.

Key words: sun: corona – MHD – methods: numerical – instabilities


© European Southern Observatory (ESO) 1997

Online publication: July 8, 1998

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