Magnetization And Levitation Characteristics Of Bulk High Temperature Superconducting Magnet

For the present high-temperature superconducting (HTS) maglev system, stable levitation and guidance forces are activated by the direct field cooling (FC) magnetization method for onboard HTS bulks above the permanent magnet guideway (PMG). The FC magnetization method for onboard HTS bulks has been facing the huge challenges with the application development, like the growing requirement of the load carrying capacity. HTS bulk has higher trapped flux than conventional permanent magnets. Current studies display HTS bulk magnets employed into the maglev system are benefit to improve levitation performances of the HTS Maglev system. At present, the force characteristics above PMGs are the main research focus but not the intra tapped flux variation during the levitation or experimental process. Therefore, the thesis arouses attention to the trapped flux variations of bulk magnet and focuses on the real-time flux variations and the related levitation performance of bulk magnets above the applied magnetic field to explore the feasibility and the stability of HTS maglev systems consisted of bulk HTS magnets.A real-time multi-point magnetic field measurement platform was firstly developed based on the growing characteristics and the magnetization characteristics of bulk high temperature superconductor (HTSC), which can be able to provide the hardware support for the following magnetization experiments and the measurement of trapped flux variations of bulk magnet. In experiments, the magnetization characteristics of HTS bulks under the constant magnetic field supplied by the LakeShore Electromagnet Supplies System was studied, including the surface magnetic field variations of HTS bulks during the magnetization process and magnetic relaxation process. And the influences of the magnetization strength and the demagnetization rate on the trapped flux of bulk magnets were analyzed as an experimental reference to the preparation of HTS bulk magnet. Then, the field variations of bulk magnets were orderly measured by the in-house real-time multi-point magnetic field measurement platform when the bulk magnets moved vertically for the levitation force measurement, horizontally for the guidance force measurement and performed the levitation force relaxation tests above the PMG. It was found that the HTS bulk magnet can be re-magnetized by the magnetic field of PMG. The influences of this re-magnetization were gradually decreased with the repetitive motion of bulk magnet, and the trapped flux and levitation performance of HTS bulk magnet finally became stable. The research results on bulk magnets with different trapped flux indicated that the levitation performance of bulk magnets can be saturated with the increase of trapped flux. For the research results on the levitation performance of bulk magnets above different patterns of PMG demonstrated that the levitation performance saturation of bulk magnets were determined by both of the magnetic field of PMG and the magnetizing current. The magnetic field of PMG is stronger, the magnetizing current provided to the levitation performance saturation smaller.Finally, the 3-D magnetization model of bulk HTSC was established by the COMSOL multi-physics software, which combines the coupling electromagnetic field and temperature field of a bulk HTS from the view of application. Base on this model, the simulation results were qualitatively analyzed and compared to the experimental results. In addition, some investigation works which cannot be done by experiment were carried out by this model, such as the demagnetization rate under strong magnetic field, trapped filed and current distribution of HTS bulks with internal defects.