Twisted magnetic flux tubes - Effect of small twist

The solar corona magnetic flux tube shape is investigated when the photospheric motion causes a small twist at the magnetic footpoints. The magnetic loops in the corona are essentially toroidal in shape and have remarkably constant cross-sectional area along their length. The length is approximately ten times the width, giving an unusually large aspect ratio. A model is developed for a toroidal coronal loop using the assumptions of constant cross section and large aspect ratio. An alternative method from that developed by Zweibel and Boozer (1985) is presented to show the effects of twisting motions at the photospheric footpoints. The method employs a Fourier-Bessel series expansion. A variety of different twist profiles is investigated, and, in all cases, a boundary layer feature is obtained.