The Application of Cryocoolers for Cooling a High-Tc SQUID Magnetometer
A multichannel high-Tc dc-SQUID based heart-magnetometer is currently under development in our laboratory. Since this system has to be simple to use, the cooling of the device should be established by means of a turn-key apparatus incorporating a cryocooler. Because of its magnetic interference, the cooler has to be separated from the SQUID unit. Therefore, an interface between the cooler and the SQUIDs is needed. Possibilities are a gas flow system or a conductive strip. A prototype closed-cycle gas flow system has been constructed and tested, in which helium gas is cooled by a Leybold Heraeus RG 210 Gifford-McMahon cryocooler. Then it is transported through a gas line of 2.5 meter length, and after that through a glass-epoxy heat exchanger on which the SQUIDs can be installed. With this system a temperature of 30 K can be established in about 2 hours (depending on the gas flow rate). Based on the results obtained with this configuration, a smaller system was designed incorporating two Signaal Usfa UP 7058 Stirling cryocoolers. Compared to the prototype the dimensions were reduced by roughly a factor 5.
In this paper the construction of the prototype system (incorporating a gas flow) is shortly described and some experimental data are presented. However, we mainly focus on the design of the follow-up system based on the two Stirling cryocoolers. We consider different approaches for interfacing the SQUID unit and the coolers, paying attention to thermodynamic aspects as well as magnetic interference.
KeywordsSquid Magnetometer Fluxgate Magnetometer Magnetic Noise Conductive Strip Cold Head
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