Vortex Reconnection in Normal and Superfluids

Abstract

We have discussed vortex reconnection in a comparative way for normal and superfluids. The dynamics at the scale of the vortex cores is rather different, and apparently much smoother for superfluids, whereas the large scale behavior of vortex filaments and rings is very much the same. Since both systems are essentially Euler fluids outside a vortex core, the latter behavior is unsurprising, and provides further evidence for the similarities between normal and superfluid turbulence.

The superfluid reconnection calculations discussed here incorporated the minimal physics needed to address the phenomena intelligently— the simplest reasonable model of the condensed state, zero temperature, and neglect of the normal fluid and mutual friction. It is our belief that in a model more realistic than GP one would see perhaps more structure in the core region, corresponding to a richer excitation spectrum, but no significant change in general behavior or vortex topology. The role of the GP model in this sense is to provide a physically reasonable smoothing of the core singularity present in an idealized line vortex, and that more refinements would just affect the details. The similarities between the superfluid and Navier-Stokes results discussed above already justify this assertion.

Adding the normal fluid and finite temperature is a very interesting avenue for further work at the atomic scale considered here, since issues such as thermal nucleation and vortex coupling to normal fluid are likely to be qualitatively significant. Similarly, the generation of vorticity due to interaction of the superfluid with solid walls would be better understood if further microscopic information were available. It would be a pleasure to hear these topics reviewed at the next meeting on superfluid vortices.