Self-modification of the remanence distribution of a hollow cylindrical permanent magnet array

Abstract

A hollow cylindrical permanent magnet array (HCPMA) used for refrigeration generates a strong magnetic field in the access hole and also inside the permanent magnets. The generated field modifies the remanence distribution of the magnets. Here, we describe a self-consistent calculation method for the remanence vectors and magnetic inductions using the Biot-Savart law. The method takes into account the anisotropic magnetization loops of commercial permanent magnets. Results obtained for the modified remanence distribution of a long HCPMA show demagnetization and deflection, including the reversal of original remanence vectors, when the generated field of the HCPMA exceeds the coercivity of the permanent magnets. The reversed remanence vectors lead to the formation of remanence vortices. In comparison with the field obtained from the ideal model assuming constant remanence vectors, remanence demagnetization and deflection result in obvious decreases in both the field magnitude and field homogeneity in the access hole. However, the field distribution in the access hole can be improved by using the magnet segments of specially high coercivity in places where large inverse or transverse fields exist. The method reported here is applicable for studying the magnetic fields, including the demagnetization, saturation, deflection, and rotation of the remanence vectors, of other permanent magnet arrays.