Studies On Levitation Force Of Bulk High Temperature Superconductor Exposed To Fluctuant External Magnetic Field Above The Permanent Magnet Guideway

The high temperature superconductor (HTSC) bulk can realize inherently self-stable levitation in external magnetic field without any active control, so the high temperature superconducting magnetic levitation (Maglev) train is more significant potential for the maglev train than the normal electromagnets maglev and the low Tc superconducting maglev. The superconductivity maglev train will be one of the transports with high-speed, safety, reliability, low environmental impact. Our group did a lot of research on high temperature superconductivting (HTS) maglev vehicle system and successfully developed the first man-loading HTS maglev test vehicle on Dec.31,2000. For the HTS maglev vehicle system, it required that the magnetic field is i mmutable along the lengthways direction. However, the permanent magnet guideway (PMG) is composed many permanent magnets, there should be air gap between the adjacent magnets, which would fluctuate magnetic field above the PMg surface. So the present thesis considers the effect of the fluctuant magnetic field on the levitation force of the HTS bulk above the PMG.For the permanent magnet guideway of the HTS Maglev vehicle system, there should be some air gaps between two adjacent permanent magnets by connecting, which may generate ripple magnetic field in the forward direction of the vehicle. The surface magnetic field of the PMG is measured and simulated by a computer. From the experimental and the simulation results, the influence of the air gap on the magnetic field above PMG is investigated.For the Maglev vehicle engineering application, we investigate the levitation force characteristics of the HTS bulk above the PMG exposed to the AC magnetic field generated by electromagnet, which is used to simulate the possible fluctuation of the PMG.Firstly, the influence of the AC field frequencies on the levitation force is investigated, according to characteristic of the levitation of HTS bulk expose the AC field above PMG., it is the first time to divide the frequencies into low-frequency, high-frequency and transition-frequency. Besides, the influence of variation of frequency of the AC field on the levitation force is investigated. Then, the oscillation and attenuation characteristic of the levitation force of the HTS bulk expose to the low-frequency AC field are investigated; based on the Bean critical model, we explained the oscillation and attenuation of the levitation force and discussed the influence of amplitude of AC field on the levitation force. We also compare the levitation fore oscillation and attenuation of the bulk exposed to the fluctuant external magnetic field under the conditions of different field-cooled height or different work height. Similarly, the characteristic of the levitation force of the HTS bulk expose to the high-frequency AC field is also investigated.Based on the Bean critical model, a simulation method is adopted to calculate the oscillation and decay of levitation force of the bulk exposed to. fluctuant magnetic field for the current HTS maglev system. Compared the experimental results with the simulation ones, it was found that the simulation method was feasibility and could qualitatively reveal the characteristics of levitation force of HTS bulk in this situation. Furthermore, the influences of. critical current density and the dimension of a superconductor on the levitation force of the bulk exposed to fluctuant magnetic field are investigated by the simulation method.