%0 Journal Article
%T Solar and Galactic Magnetic Halo Structure: Force-Free Dynamos?
%A Richard Henriksen
%J Galaxies | An Open Access Journal from MDPI
%D 2019
%R https://doi.org/10.3390/galaxies7020053
%X Magnetic fields may relax dissipatively to the minimum energy force-free condition whenever they are not constantly created or distorted. We review the axially symmetric solutions for force-free magnetic fields, especially for the non-linear field. A new formulation for the scale invariant state is given. Illustrative examples are shown. Applications to both stellar coronas and galactic halos are possible. Subsequently we study whether such force-free fields may be sustained by classical magnetic dynamo action. Although the answer is `not indefinitely¡¯, there may be an evolutionary cycle wherein the magnetic field repeatedly relaxes to the minimum energy condition after a period of substantial growth and distortion. Different force-free dynamos may coexist at different locations. Helicity transfer between scales is studied briefly. A dynamo solution is given for the temporal evolution away from an initial linear force-free magnetic field due to both ¦Á 2 and ¦Ø terms. This can be used at the sub scale level to create a `delayed¡¯ ¦Á effect. View Full-Tex
%U https://www.mdpi.com/2075-4434/7/2/53