Magnetic shielding effects of the superposition ofa ferromagnetic cylinder over an HTS cylinder:Magnetic shielding dependence on the wall thickness ofthe ferromagnetic cylinder

摘要

The present research has demonstrated the improvement in thernvalue of the maximum shielded magnetic flux density Bs by thernsuperposition of a soft-iron cylinder over a BPSCCO cylinder, termed thernsuperimposed cylinder. The values of Bs were measured for changes in thernwall thickness W of the soft-iron cylinder, and were also theoreticallyrnanalyzed. The experimental values of Bs agreed well with the theoreticalrnvalues. However, the inner magnetic flux density Bin and magneticrnfluctuation of Bin within the superimposed cylinder when changing thernvalue of W, under the application of an excitation magnetic flux densityrnBex less than the value of Bs, were not previously known. To help clarifyrnthese problems, systematic measurements were taken of the magneticrnnoise power (MNP) spectrum, and the values of Bin for various values ofrnW, with the use of an HTS dc-SQUID system and a spectrum analyzer.rnThe results lead to an important criterion for use in the design of a highlyrneffective magnetic shielding vessel having high reliability.