Smooth vortex precession in superfluid 4 He

We use a vibrating wire to trap circulation in superfluid 4 He. When the trapped circulation extends along only part of the wire, continuing as a free vortex through the cell, we can observe the free vortex precessing around the wire. Despite the small vortex core size in superfluid 4 He, the vortex motion proceeds in a regular manner, negotiating surface asperities without halting. We attribute this smooth precession to the wire's being substantially displaced from the cylinder's axis. We verify several numerical predictions about the motion, including an asymmetric signature, isolated pinning events, and temperature dependence.