Unpinning triggers for superfluid vortex avalanches

TL;DR

This paper investigates the mechanisms triggering superfluid vortex avalanches, crucial for understanding neutron star glitches, using numerical simulations to identify key unpinning triggers like shear, vortex proximity, and sound waves.

Contribution

It explicitly identifies and analyzes three primary triggers for vortex unpinning events through Gross-Pitaevskii simulations, advancing understanding of superfluid vortex dynamics.

Findings

Sound waves can unpin nearby vortices when dissipation is low.

Maximum inter-vortex separation for unpinning scales inversely with pinning strength.

Identified three key triggers: shear, vortex proximity, and sound waves.

Abstract

The pinning and collective unpinning of superfluid vortices in a decelerating container is a key element of the canonical model of neutron star glitches and laboratory spin-down experiments with helium II. Here the dynamics of vortex (un)pinning is explored using numerical Gross-Pitaevskii calculations, with a view to understanding the triggers for catastrophic unpinning events (vortex avalanches) that lead to rotational glitches. We explicitly identify three triggers: rotational shear between the bulk condensate and the pinned vortices, a vortex proximity effect driven by the repulsive vortex-vortex interaction, and sound waves emitted by moving and repinning vortices. So long as dissipation is low, sound waves emitted by a repinning vortex are found to be sufficiently strong to unpin a nearby vortex. For both ballistic and forced vortex motion, the maximum inter-vortex separation required to unpin scales inversely with pinning strength.