Spherically symmetric counterflow turbulence in open geometry

Abstract

We report preliminary results on spherical thermal counterflow generated by a small central heater in an open geometry, an open bath of superfluid He~II, as closed-cell experiments could have introduced artifacts such as overheating and boundary-induced flows. In order to eliminate them, we measure second sound attenuation in a plane-parallel resonator. Our results are at variance with the previous experiments in closed spherical cavity that showed plateau in the steady-state vortex line density and its inverse time decay, neither of which is observed presently. We find that in open geometry the vortex line density $L$ increases steadily with counterflow velocity $v_{\mathrm{ns}}$, displaying a crossover between $L\propto v_{\mathrm{ns}}^2$ typical for counterflow and $L\propto v_{\mathrm{ns}}^{3/2}$, characteristic for the quasi-classical scaling.

11 pages, 5 figures