Stable Vortex Configurations in a Cylinder
  We calculate stable arrangements for a single superfluid vortex pinned to the wall of a stationary cylindrical container. We find that, independent of the details of the pinning site, stable vortices must subtend most of the cell horizontally and cannot be vertical or nearly vertical. More generally, the geometry of a container severely limits the possible vortex configurations, making macroscopic trapped vortices less common than previously believed. 
R. J. Zieve and L. A. K. Donev