Large-scale superfluid vortex rings at nonzero temperatures

Abstract

We numerically model experiments in which large-scale vortex rings---bundles of quantized vortex loops---are created in superfluid helium by a piston-cylinder arrangement. We show that the presence of a normal-fluid vortex ring together with the quantized vortices is essential to explain the coherence of these large-scale vortex structures at nonzero temperatures, as observed experimentally. Finally we argue that the interaction of superfluid and normal-fluid vortex bundles is relevant to recent investigations of superfluid turbulence.