Instability and Vortex Rings Dynamics in a Three-Dimensional Superfluid Flow Through a Constriction

TL;DR

This paper investigates the onset of instability and vortex ring formation in a three-dimensional superfluid flow through a constriction, revealing critical velocities and the influence of asymmetries in the flow.

Contribution

It provides a detailed analysis of vortex ring nucleation and dynamics in superfluid flow through constrictions, highlighting the role of flow asymmetries and critical velocities.

Findings

Flow becomes unstable when velocity equals sound speed at the constriction.

Vortex rings enter the superfluid at the critical velocity.

Asymmetries significantly influence vortex nucleation and dynamics.

Abstract

We study the instability of a superfluid flow through a constriction in three spatial dimensions. We consider a Bose-Einstein condensate at zero temperature in two different geometries: a straight waveguide and a torus. The constriction consists of a broad, repulsive penetrable barrier. In the hydrodynamic regime, we find that the flow becomes unstable as soon as the velocity at the classical (Thomas-Fermi) surface equals the sound speed inside the constriction. At this critical point, vortex rings enter inside the bulk region of the cloud. The nucleation and dynamics scenario is strongly affected by the presence of asymmetries in the velocity and density of the background condensate flow.