Reduction of the Vibration Generated by Stirling Cryocoolers Used for Cooling a High-Tc SQUID Magnetometer
Recently a research project was started to realize magnetocardiography in clinical conditions by means of high-Tc SQUID magnetometry (SQUID for Superconducting Quantum Interference Device). The cooling of the SQUID-devices involved will be performed by a pair of dual opposed Stirling type cryocoolers each consisting of separate compressor and displacer modules. Since the magnetic signals from the human heart are quite small (10 – 100 pT), important problems to cope with are interferences from external magnetic fields and magnetic disturbances due to the vibratory motion of the cryocooler components. In the paper we consider the reduction of the vibrations generated by the coolers. It is shown that an effective vibration reduction is achieved by 1) a dual opposed arrangement of the two displacer modules, mounted in a rigid construction; 2) a flexible mounting of the compressors and displacer unit; and 3) manual tuning of the currents of the compressor coils leading to highly balanced motions of the various parts. As a result the axial acceleration of a single compressor was reduced by a factor of 20 down to 0.05 m/s2, whereas for the displacer unit a reduction by a factor of 25 down to 0.02 m/s2 was obtained.
KeywordsVibratory Motion Squid Magnetometer Coil Current Vibration Reduction Magnetic Noise
Unable to display preview. Download preview PDF.
- 1.Van den Bosch, P.J., Holland, H.J., Ter Brake, H.J.M. and Rogalla, H., A closed-cvcle gas flow system for cooling a HTc DC-SQUID magnetometer. Proc. CEC, Albuquerque (1993).Google Scholar
- 2.Van den Bosch, P.J., Ter Brake, H.J.M., Van den Eijkel, G.C., Boelens, J.P., Holland, H.J., Verberne, J.F.C. and Rogalla, H., Thermodynamics of a closed-cvcle gas flow system for cooling a HTc DC-SQUID magnetometer. Proc. ICEC, Genova (1994).Google Scholar
- 3.Ter Brake, H.J.M., Van den Bosch, P.J. and Holland, H.J., Magnetic noise of small Stirling coolers. Proceedings of CEC, Albuquerque (1993).Google Scholar
- 4.Van den Bosch, P.J., Aarnink, W.A.M., De Boer, H.A., Holland, H.J., Ter Brake, H.J.M. and Rogalla, H., The application of cryocoolers for cooling a high-Tc SQUID magnetometer. Proc. of the 8-th Int. Cryocooler Conf, Vail, Colorado (1994).Google Scholar
- 5.Boyle, R., Connors, F., Marketon, J., Arillo, V., James, E. and Fink, R., Non-real time, feed forward vibration control system development & test results. Proc. of the 7-th Int. Cryocooler Conf., Santa Fe, NM, (1992), pp. 805-819.Google Scholar
- 7.Verbeek, D., Helmonds, H., and Roos, P., Performance of the Signaal Usfa Stirling cooling engines. Proc. of the 7-th Int. Cryocooler Conf. Santa Fe, NM, (1992), pp. 728-737.Google Scholar
- 8.Signaal Usfa, P.O.box 6034, NL-5600HA Eindhoven, The Netherlands.Google Scholar
- 9.De Jonge A.K., A small free-piston Stirling refrigerator. Proc. of the 14-th IECEC, Am. Chem. Soc., Washington D.C, (1979), pp. 1136-1141.Google Scholar