Quantum turbulence of bellows-driven 4He superflow: Steady state

Quantum turbulence in superfluid He-4 is studied by the attenuation of second sound in flow channels of 7-mm and 10-mm side square cross sections, and 115-mm length. The ends of the channels are plugged by sintered silver superleaks to allow a pure superflow (i.e., a net flow of the superfluid component only). Flows are generated by mechanically operating a low temperature bellows assembly, as opposed to the helium fountain pump commonly used for previous superflow turbulence studies. The temperature range is 1.35 K <= T <= 1.95 K, at the saturated vapor pressure. The observed turbulent steady state is characterized by the vortex line density L-1/2 = gamma(T)(v - v(c)), where v is the mean superflow velocity and v(c) is the critical velocity for the onset of turbulence. The character of the steady state agrees with the Vinen phenomenological model for thermal counterflow turbulence. The coefficient gamma(T) is in fair agreement with previous thermal pure superflow and counterflow experiments. The critical velocity v(c) approximate to 0.2 cm/s is roughly temperature independent.