Magnetic evaluation of HTS magnetic shielding cylinders using an HTS dc-SQUID

For practical applications, an ideal magnetic shielded vessel can be realized by making use of a high-critical temperature superconductor (HTS). Generally, the value of the maximum shielded magnetic flux density B/sub s/ is used to evaluate the magnetic shielding effect of the HTS vessel. Little is known, however, of the characteristics and evaluation procedures used to determine the behavior of the magnetic flux density B/sub in/ within the shielded vessel when exposed to an external magnetic flux density B/sub ex/ of less than the value of B/sub s/. In order to evaluate the behavior of the magnetic field within the Bi-Pb-Sr-Ca-Cu-O cylinder to an applied B/sub ex/ the temporal change of B/sub in/, and the magnetic noise power spectrum (NPS) of B/sub in/ are measured by an HTS dc-SQUID magnetometer and spectrum analyzer. The present paper examines the optimum shielding conditions for constructing an ideal magnetic shielding vessel.