抄録
To develop a small, light, and highly reliable cooling system for a Nb-based SQUID (Superconducting QUatum Interference Device) magnetometer, we measured the magnetic noise produced by a Gifford-McMahon (GM) cycle cryocooler containing magnetic regenerative material, Er3Ni, and calculated the magnetic field around the regenerator by integral computation. Both results showed that the GM cryocooler containing magnetic regenerative material such as Er3Ni was able to be used for SQUID systems for biomagnetic measurement. The GM cryocooler with Er3Ni was installed in a GFRP cryostat. Two SQUID magnetometers were mounted in this cryostat and the magnetic noise produced by the GM cryocooler was measured in a magnetically-shielded room. Intensity of the magnetic noise was about 40pT p-p. It was about six times the value expected from the results measured under the earth magnetic field. So we eliminated the magnetic noise by digital filtering and magnetocardiogram (MCG) and auditory evoked magnetoencephalogram (MEG) were successfully measured.
