Ideal kink instability of a magnetic loop equilibrium
Bernhard Kliem Submitted: 2003-11-06 17:26
The force-free coronal loop model by Titov & D'emoulin (1999) is found
to be unstable with respect to the ideal kink mode,
which suggests this instability as a mechanism for the initiation of flares.
The long-wavelength (m=1) mode grows for average
twists Phi gtrsim 3.5pi (at a loop aspect ratio of approx 5).
The threshold of instability increases with increasing
major loop radius, primarily because the aspect ratio then also increases.
Numerically obtained equilibria at subcritical twist are very close to the
approximate analytical equilibrium; they do not show indications of
The growth of kink perturbations is eventually slowed down by the surrounding
potential field, which varies only slowly with radius in the model. With
a global eruption is not obtained in the ideal MHD limit. Kink
perturbations with a rising loop apex lead to the
formation of a vertical current
sheet below the apex, which does not occur
in the cylindrical approximation.
(See animation at http://www.aip.de/~kli/Fi252.gif)
Authors: T. Toeroek, B. Kliem, and V. S. Titov
Publication Status: Astron. Astrophys. Lett., accepted
Last Modified: 2003-11-07 15:51