Closed-cycle gas flow system for cooling a HTc dc-SQUID magnetometer

P.J. Bosch, van den, H.J. Holland, H.J.M. Brake, ter, H. Rogalla

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    A closed-cycle gas flow system for cooling a high-crit. temp. d.c.-superconducting quantum interference device (SQUID) magnetometer by means of a cryocooler has been designed, constructed and tested. The magnetometer is aimed to measure heart signals with a sensitivity of 0.1 pT/Hz1/2. The required operating temp. of the SQUID is 30-70 K with a stability of 0.5 K. Allowing for a cool-down time of about one hour a cooling power of at least 0.2 W is required (sensor mass .apprx. 2 g). Further requirements for the system are a low vibration level and a low magnetic interference. In the design, helium gas is forced to flow in a closed cycle by means of a gas-flow pump. The gas is cooled by a Leybold Heraeus RG 210 cooler, transported through a gas line, and cools the SQUID in a glass-epoxy heat exchanger. The return gas is used to thermally insulate the supply gas. Because the gas-flow pump has to operate at room temp., a counterflow heat exchanger has been incorporated. Based on the experience with this cooling system, a much smaller configuration using a miniature Stirling cryocooler will be designed. The design and construction of the present closed-cycle system is described and first test results are presented. [on SciFinder (R)]
    Original languageEnglish
    Pages (from-to)1647-1655
    JournalAdvances in Cryogenic Engineering
    Issue numberPt. B
    Publication statusPublished - 1994


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