Dissipation of Quasiclassical Turbulence in Superfluid $^4$He

TL;DR

This study compares how different methods of generating turbulence in superfluid helium-4 decay over time, revealing temperature-dependent differences likely due to changes in flow boundary conditions.

Contribution

It provides a comparative analysis of turbulence decay in superfluid helium-4 produced by various methods across a range of temperatures, highlighting the impact of temperature on decay dynamics.

Findings

All methods show a vortex line density decay as t^{-3/2} at late times.

Above 0.8 K, decay rates are similar regardless of turbulence generation method.

Below 0.8 K, spin-down turbulence decays slower and retains initial rotation.

Abstract

We compare the decay of turbulence in superfluid $^4$He produced by a moving grid to the decay of turbulence created by either impulsive spin-down to rest or by intense ion injection. In all cases the vortex line density $L$ decays at late time $t$ as $L \propto t^{-3/2}$. At temperatures above 0.8 K, all methods result in the same rate of decay. Below 0.8 K, the spin-down turbulence maintains initial rotation and decays slower than grid turbulence and ion-jet turbulence. This may be due to a decoupling of the large-scale superfluid flow from the normal component at low temperatures, which changes its effective boundary condition from no-slip to slip.