Decay of turbulence generated by spin-down to rest in superfluid 4He

TL;DR

This study investigates how turbulence in superfluid helium-4 decays after impulsive spin-down, revealing the dynamics of vortex density and turbulence spreading at various temperatures.

Contribution

The paper extends previous experiments by analyzing the transient turbulence spreading and decay in superfluid helium-4 across a range of temperatures, including the zero-temperature limit.

Findings

Vortex density peaks around 10 Omega^-1 after spin-down.

Nearly homogeneous turbulence develops after about 100 Omega^-1.

Vortex line density decays as t^(-3/2) with an effective viscosity of 0.003 kappa.

Abstract

We report on the extension of the experiments (P. M. Walmsley et al., Phys. Rev. Lett. 99, 265302 (2007)) on the decay of quasiclassical turbulence generated by an impulsive spin-down from angular velocity Omega to rest of superfluid 4He in a cubic container at temperatures 0.15 K - 1.6 K. The density of quantized vortex lines L is measured by scattering negative ions. Following the spin-down, the maximal density of vortices is observed after time t ~ 10 Omega^-1. By observing the propagation of ions along the axis of the initial rotation, the transient dynamics of the turbulence spreading from the perimeter of the container into its central region is investigated. Nearly homogeneous turbulence develops after time t ~ 100 Omega^-1 and decays as L proportional to t^(-3/2). The effective kinematic viscosity in T=0 limit is nu = 0.003 kappa, where kappa=10^-3 cm^2 / s is the circulation quantum.