The growing need for refrigeration at temperatures below the boiling point of helium—particularly to maintain superfluid helium in a superconducting linear accelerator for long periods of time—has led to the development of a closed‐cycle refrigerator in which the refrigerative powers of the helium vapor at pressures as low as 0.02 atm can be utilized. Effective use of the cold vapor in a heat exchanger makes possible a several‐fold increase in the capacity of a refrigerating system, as compared to conventional open‐cycle techniques.