Low-frequency magnetic interference in a SQUID gradiometer caused by a Cryotiger® gas-mixture cooler

Rijpma, A.P. and Brake ter, H.J.M. and Vries de, E. and Holland, H.J. and Rogalla, H. (2005) Low-frequency magnetic interference in a SQUID gradiometer caused by a Cryotiger® gas-mixture cooler. Cryogenics, 45 (4). pp. 317-322. ISSN 0011-2275

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Abstract:	A Cryotiger® gas-mixture cooler was applied for cooling of three high-Tc SQUID magnetometers. These SQUID magnetometers were mounted on an alumina holder in an axial gradiometer configuration. From 20 Hz upward, the system noise was about 0.1 pT/√Hz. Below this frequency, the noise gradually increased to a level of 10 pT/√Hz at 1 Hz. This low-frequency excess noise appeared to be due to remnant magnetization of the Cryotiger cold head. Movement of magnetic cold-head parts with respect to the SQUIDs are induced by pressure fluctuations in the heat exchanger lines. By using one SQUID as a reference for the cooler noise, a first-order gradiometer can be formed in which the cooler noise is eliminated. To establish a proper second-order gradiometer either a fourth SQUID has to be added, or the spatial separation between cold head and SQUIDs has to be increased significantly.
Item Type:	Article
Copyright:	© 2005 Elsevier
Faculty:	Science and Technology (TNW)
Research Group:	Low Temperatures - Biomagnetism (LT)
Link to this item:	http://purl.utwente.nl/publications/77767
Official URL:	http://dx.doi.org/10.1016/j.cryogenics.2004.11.009
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