Relaxation Of Levitation Force Of The YBCO Bulk Above Permanent Magnet Guideway

Since the discovery of superconductivity by Onnes in 1911 to the discovery of high-temperature superconductors (HTSCs) in 1986, many investigations on superconducting material and its applications were carried out. Because of the self-stability of high-temperature superconducting (HTS) maglev system there are many potential applications, such as Maglev vehicle, flywheel, bearing, motor, and so on.However, researchers found the hysteresis phenomenon of HTSC exposed to the applied magnetic field. Macroscopically, this behavior is represented by the levitation force decays with time. It will affect the stability of HTS levitation system. In practical application, durative is as important as stability of the HTS Maglev vehicle system. Therefore, magnetic relaxation and physical properties of HTSCs are needed to careful study. In the paper, levitation force relaxation phenomenon of the YBCO bulks above permanent magnet guideway (PMG) was investigated by both experiment and simulation.Experimentally, we invesitgated the relaxation of levitation force of the single YBCO bulk and seven YBCO bulks respectively at the same filed cooling height (FCH) but different working heights (WHs), the same WH but different FCHs and different testing processes. When FCH is constant, the lower WH is, the bigger relaxation amplitude of the levitation force gets. While, in the case of constant WH, FCH has no significant impact on the force relaxation. In the experimental condition of different testing processes, it is found that the relaxation of levitation force will be reduced if we move the bulk back a little before end stop. So we can use the reverse motion to reduce the levitation force relaxation of levitation system under field cooling conditions. Moreover, the influence of different PMG field on force relaxation was also investigated. It is found that bigger magnetic field gradient will bring bigger levitation force relaxation.Finally, the rule of levitation force relaxation of HTSC was simulated by a numerical model. The curve law of simulation results agree well with the experimental results. Using the model, the testing speed on the levitation force relaxation was also analyzed. It is found that the testing speed has impact on the strength of the levitation force and the peak time, and the faster testing speed, the faster levitation force change.