Experiments on Pumping Liquid Helium to Low Temperatures

Abstract

TEMPERATURES sensibly lower than those usually attained by pumping liquid helium are accessible now that the design of apparatus can take into account the known characteristics of the creeping film phenomenon¹ of liquid helium II. In a previous paper² it was shown that temperatures below 0.8° K. could be reached very simply by constricting the lower part of the pumping tube, to restrict the creeping of the helium II film. We suggested that still lower temperatures might be attained by using a membrane pierced by a small hole instead of the constriction tube. The advantage of this design is that it reduces the film flow while offering the minimum impedance to the flow of gas evaporating from the surface of the liquid owing to the normal heat influx.