Possible visualization of a superfluid vortex loop attached to an oscillating beam

Abstract

Visualization using tracer particles is a relatively new tool available for thestudy of superfluid turbulence and flow, which is applied here to oscillating objectssubmerged in the liquid. We report observations of a structure seen in videos takenfrom outside a cryostat filled with superfluid helium at 2 K, which is possibly a vortexloop attached to an oscillator. The feature, which has the shape of an incomplete arch,is visualized due to the presence of solid H2 tracer particles and is attached to a beamoscillating at 38 Hz in the liquid. It has been recorded in videos taken at 240 frames persecond, fast enough to take ∼6 images per period. This makes it possible to follow thestructure, and to see that it is not rigid. It moves with respect to the oscillator, and itsdisplacement is in phase with the velocity of the moving beam. Analyzing the motion,we come to the conclusion that we may be observing a superfluid vortex attached tothe beam and decorated by the hydrogen particles. An alternative model, consideringa solid hydrogen filament, has also been analyzed, but the observed phase betweenthe movement of the beam and the filamentary structure is better explained by thesuperfluid vortex hypothesis.