Crow instability of vortex lines in dipolar superfluids

TL;DR

This paper investigates how dipole-dipole interactions influence the Crow instability of quantum vortex lines in dipolar superfluids, revealing the role of dipole orientation in vortex dynamics and potential turbulence mechanisms.

Contribution

It provides the first mean-field simulation analysis of Crow instability in dipolar superfluids, highlighting the impact of dipole polarization on vortex behavior and instability rates.

Findings

Dipole polarization direction critically affects Kelvin mode stability.

Vortex curvature and instability rate depend on dipole orientation.

Modes of different wavenumbers are favored based on polarization direction.

Abstract

In classical inviscid fluids, antiparallel vortices perturbed by Kelvin waves exhibit the Crow instability, where the mutual interaction of the Kelvin modes renders them dynamically unstable. This results in the approach and reconnection of the vortices, leading to a cascaded decay into ever-smaller vortex loops. Through mean-field simulations we study the Crow instability of quantum vortex lines in a superfluid whose atoms are subject to the anisotropic, long-ranged dipole-dipole interaction. We observe that the direction of dipole polarization plays a crucial role in determining the dynamically favored Kelvin modes. The subsequent rate of the instability is linked to the mediation of the vortex curvature by the effective dipole-dipole interaction between the vortices themselves. The vortex curvature is strongly suppressed and modes of lower wavenumber are preferred when the dipole polarization is parallel to the vortices, whereas the curvature is maximized for polarizations along the vortices' separation axis. For polarizations along the binormal axis, modes of higher wavenumber are favorable but the instability rate is considerably inhibited. This paves the way to a deeper understanding of vortex reconnections, vortex loop cascades and turbulence in dipolar superfluids.