Peculiarities of Spherically Symmetric Counterflow

Thermal counterflow in superfluid 4 He (He II) was studied numerically using the vortex filament model in a spherically symmetric geometry (as resulting from a point heat source). It is found that for the range of temperatures and velocities studied, turbulent tangle of the quantised vortices develops only for sufficiently low temperatures, hinting at the existence of a critical temperature, and only for velocities bounded from above (and presumably from below). A velocity–temperature phase diagram is presented. A simple physical model is proposed that qualitatively explains both observations.