Temperature and Level Control in a Liquid Helium II Cryostat

  • A. Elsner
  • G. Klipping
Part of the Advances in Cryogenic Engineering book series (ACRE, volume 18)


Since He II has recently assumed increasing importance as a cooling medium for long-term runs and higher heat loads, further consideration has been given to a He II refilling device described earlier [1]. This device (Fig. 1) permits control of the liquid level h 1 as well as the temperature T 1 of the He II bath in C 1, the lower chamber of the cryostat. The temperature is kept constant by a pressure controller while the liquid level is restored at periodic time intervals depending on the heat load in the He II bath and on the dimensions of the cryostat. This is accomplished by refilling the upper chamber C 2 with He I and then lowering the temperature of the fluid in this chamber slightly below that in the He II bath. The resulting superfluid in chamber C 2 flows through the filter (pore size, 10−5 to 10−4 cm) into C 1. For a positive temperature difference across the filter, T 2T 1, no liquid helium flows through the filter; whereas, for a negative temperature difference the filter is permeable. Thus, the filter acts as a temperature-controlled valve for He II. This effect is known as the fountain effect and is shown in Fig. 2, where the specific mass flow of helium through a 5-mm-thick filter, \(\dot{M}/A\), is plotted vs. the temperature difference across the filter for a constant temperature of the He II bath.


Heat Load Liquid Helium Liquid Level superflUId Helium Expansion Valve 
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  1. 1.
    A. Elsner and G. Klipping, in: Advances in Cryogenic Engineering, Vol. 14, Springer Science+Business Media New York (1969), p. 416.Google Scholar
  2. 2.
    A. Elsner, Ph.D. Dissertation, Freie Universität, Berlin, Germany (1969).Google Scholar

Copyright information

© Springer Science+Business Media New York 1973

Authors and Affiliations

  • A. Elsner
    • 1
  • G. Klipping
    • 1
  1. 1.Fritz-Haber-InstitutMax-Planck-GesellschaftBerlinGermany

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