LIQUID HELIUM-II COUNTERFLOW IN A TUBE PACKED WITH ANGULAR PARTICLES AND APPLICATION AS A SUPERFLUID PUMP

Observations are reported on the operation of a recirculating superfluid **4He pump capable of driving a stable superfluid flow from subcritical continuously through a wide range of chemical potential head, ranging from very small to moderately large. The pump consists of a superfluid path shunting a thermal counterflow tube. The latter is packed with coarse angular particles, which generate quantized vorticity at a low and reproducible superfluid velocity in the tube, and so improve control of the superfluid flux in the shunt. A limited study was made of the tube characteristic for conditions other than pure counterflow as a basis for analyzing the pump operation. Applied to a study of the onset of dissipation in an external sample, this pump proved convenient and free of long relaxation times. Some precautions must be taken in matching the counterflow tube to the sample, to avoid regions of possible instability.