MEASUREMENTS OF THE MAGNETIC NOISE SPECTRA IN HTS CYLINDERS FOR MAGNETIC SHIELDING

;Idealized magnetic shielded vessels can be realized by use of high-cr itical temperature superconductors (HTS). It is, however, generally, v ery difficult to evaluate the limit of the value of magnetic shielding and the fluctuation of the magnetic nux within the HTS vessel. in thi s present research, the magnetic noise power spectra (NPS) within the Bi-Pb-Sr-Ca-Cu-O (BPSCCO) cylinder was measured using a HTS dc-SQUID, under an application of a magnetic held B-ex less than the value of B- s (the maximum shielded magnetic nux density, 33 x 10(-4) T at 77.4 K) . The value of NPS was determined as 5.0 x 10(-6) Phi(0)(2)/Hz at 1 kH z excluding B-ex which was the background noise of the SQUID control s ystem, and 1.0 x 10(-5) Phi(0)(2)/Hz at 1 kHz for a B-ex of 3.0 x 10(- 4) T. The value of NPS at 1 kHz increased linearly with values of B-ex in the region of 0.0 T to 3.0 x 10(-4) T. Also shown are the importan t criteria for the design of effective shielded vessels for low magnet ic measurements.