Dissipation of Quasiclassical Turbulence in Superfluid $^4$He

We compare the decay of turbulence in superfluid 4He produced by a moving grid to the decay of urbulence 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 approximately as L / -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.