Experiment Study Of The High Temperature Superconducting Permanent Magnet Properties

Pinning centers, that are some abnormal regions in type II superconductors, will hinder the flux motion. Certain of remnant magnetism in a superconductor will make it to a superconducting permanent magnet. The high magnetic field, high (BH)max value and well magnetic stability are important characteristics for its practical applications. In this thesis, melt-textured YBCO bulk superconductors are used to make high temperature superconducting (HTS) permanent magnets by magnetizing it in different applied field. At first, the interactions of HTS permanent magnet and applied field are studied, that is the levitation force of YBCO bulks over the NdFeB guideway and the influences of the applied field to the HTS permanent magnet. Secondly, the pulsed field magnetization properties of YBCO bulks are studied. At last, the influence of the sample's thickness, shape as well as the density to the levitation force over the NdFeB guideway and the trapped flux of YBCO bulk are studied.From all above studies, we can conclude that:The magnetic field of HTS permanent magnet is easily be influenced by the applied field. When it is placed in a high-applied field, the magnetic field of it will be enhanced or decreased.In pulsed field magnetization condition, we find some new phenomena characteristic, that is, the trapped fluxes of YBCO bulk increase with increasing intensity of applied field up to about 1.9T, but decease beyond this value and the scanning distribution map of the trapped fluxes on the surface of the superconductor is not slick, which is different with the superconductors magnetized in constant magnetic field and the normal permanent magnets.For HTS MAGLEV vehicle, cylindrical bulk superconductors with the thickness of 25mm are better to provide enough guidance force and keep enough levitation height when they are field cooled above the NdFeB guideway.The trapped flux ability of superconductors is influenced by the weak links and critical current density and can be reflected by the levitation force. It has no direct relationship with its density.