Abstract
Small Stirling-type cryocoolers are available on the market mainly for cooling infrared detectors, but they can also be used to cool high-Tc superconducting devices, like SQUIDs. Because SQUIDs are extremely sensitive magnetic sensors it is questionable whether these devices can be mounted directly on the cold tip of the cooler. To investigate this we attached a high-Tc SQUID to the tip of a representative split Stirling-cycle cryocooler (Signaal Usfa type 7058), and operated it in a magnetically shielded room.
The SQUID that we used for our test experiments was one of the first high-Tc SQUIDs that were manufactured in our group and had a noise level of 0.7 pT/√Hz at about 77 K. With the SQUID attached to the tip of the cold head and the cooler running, the noise appeared to have increased dramatically: at the driving frequency of 50 Hz and at the harmonics by roughly 5.105, and at other frequencies by about a factor 103. The experiments indicated that the noise coupled into the SQUID was dominated by contributions originating from the cold head, and not by compressor interference. The experiments are discussed, and the consequences with respect to the cooling of SQUIDs with standard cryocoolers are briefly considered.
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ter Brake, H.J.M., Holland, H.J., Rogalla, H. (1997). Stirling Cooler Magnetic Interference Measured by a High-Tc SQUID Mounted on the Cold Tip. In: Ross, R.G. (eds) Cryocoolers 9. Springer, Boston, MA. https://doi.org/10.1007/978-1-4615-5869-9_104
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DOI: https://doi.org/10.1007/978-1-4615-5869-9_104
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