Quasiparticle scattering measurements of laminar and turbulent vortex flow in the spin-down of superfluid 3He-B

TL;DR

This study investigates vortex dynamics in superfluid 3He-B after spin-down, revealing how deviations from symmetry induce turbulence and how vortex polarization influences dissipation and flow behavior at ultra-low temperatures.

Contribution

It provides new insights into vortex decay, turbulence onset, and dissipation mechanisms in superfluid 3He-B at very low temperatures, using quasiparticle scattering measurements.

Findings

Turbulence causes an overshoot in vortex density during spin-down.

High vortex polarization suppresses turbulent viscosity, leading to laminar flow.

Vortex dissipation approaches a temperature-independent limit below 0.15Tc.

Abstract

The dynamics of quantized vortices is studied in superfluid 3He-B after a rapid stop of rotation. We use Andreev reflection of thermal excitations to monitor vortex motion with quartz tuning fork oscillators in two different experimental setups at temperatures below 0.2Tc. Deviations from ideal cylindrical symmetry in the flow environment cause the early decay to become turbulent. This is identified from a rapid initial overshoot in the vortex density above the value before the spin-down and its subsequent decay with a t^(-3/2) time dependence. The high polarization of the vortices along the rotation axis significantly suppresses the effective turbulent kinematic viscosity below the values reported for more homogeneous turbulence and leads to a laminar late-time response. The vortex dissipation down to T < 0.15Tc is determined from the precession frequency of the polarized vortex configuration. In the limit of vanishing normal component density, the laminar dissipation is found to approach a temperature-independent value, whose origin is currently under discussion.