Spin-up of a superfluid vortex lattice driven by rough boundaries

We study numerically the formation of a vortex lattice inside a rotating bucket containing superfluid helium, paying attention to an important feature which is practically unavoidable in all experiments: The microscopic roughness of the bucket's surface. We model this using the Gross-Pitaevskii equation for a weakly interacting Bose gas, a model which is idealized when applied to superfluid helium but captures the key physics of the vortex dynamics which we are interested in. We find that the vortex lattice arises from the interaction and reconnections of nucleated U-shaped vortex lines, which merge and align along the axis of rotation. We quantify the effects which the surface roughness and remanent vortex lines play in this process.