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 thevalue of the maximum shielded magnetic flux density Bs by thesuperposition of a soft-iron cylinder over a BPSCCO cylinder, termed thesuperimposed cylinder. The values of Bs were measured for changes in thewall thickness W of the soft-iron cylinder, and were also theoreticallyanalyzed. The experimental values of Bs agreed well with the theoreticalvalues. However, the inner magnetic flux density Bin and magneticfluctuation of Bin within the superimposed cylinder when changing thevalue of W, under the application of an excitation magnetic flux densityBex less than the value of Bs, were not previously known. To help clarifythese problems, systematic measurements were taken of the magneticnoise power (MNP) spectrum, and the values of Bin for various values ofW, with the use of an HTS dc-SQUID system and a spectrum analyzer.The results lead to an important criterion for use in the design of a highlyeffective magnetic shielding vessel having high reliability.