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Characterization of levitation force for a superconducting magnetic levitation vehicle

Background: In Superconducting Magnetic Levitation (SML) transportation systems, such as the MagLev-Cobra prototype, the levitation force plays an important role, both for efficiency and safety reasons. 
Aim: Determination of the maximum load on the magnetic suspension. 
Methods: To determine how much load the magnetic suspension system supports, numerical simulations, based on computational models, and laboratory experimental tests are normally used. 
The most commonly way for characterization of a SML bearing is the measurement of the levitation force as a function of distance between a Superconductor (YBCO) [1, 2] and a Permanent Magnet Guideway (PMG). The measurement of levitation as a function of distance, the banana curve, has a hysteretic behavior with the results depending of the history of measurement: whether the distance between the superconductor and the PMG is decreasing the force is higher than when the distance is increasing, the force is higher with faster movements and so on. A different approach of levitation force test will be proposed as an alternative to the hysteresis curve. This method, applied to characterize the levitation dynamics of the Maglev-Cobra vehicle, provided more reliable and consistent data with the levitation dynamics observed during the operation of the real scale prototype in the transportation of passengers. 
The bench-top levitation test emulates the behavior of the vehicle along its operation, regardless of the position history between the magnets and the superconductor materials. The test consists in placing the superconductor, refrigerated inside cryostats, in a predetermined Field Cooling (FC) position, and slowly move the cryostat above the PMG to a lower high, for example 15 mm, and wait 10 minutes. After that, the high is decreased 1 mm and again hold there for 10 minutes. The procedure is repeated until a high of 10 mm is reached. The hole process is repeated at least 5 times. This routine replicates the load condition during the vehicle operation when passengers board the train and the load stay constant until the end of the journey. After that, another group of passengers takes place inside the vehicle and is carried to the next station. 
This kind of test shows the creep of the levitation force over time with slow dynamics and gives the average load over height of levitation along the given time of operation, helping engineers to predict the load capacity of the vehicle and design a more reliable layout. 
Results: Three FC positions were investigated. The position currently used by the MagLev-Cobra (35 mm) and other 2 positions (45 mm and 55 mm) of initial height between the superconductor and the permanent magnet guideway. 
Conclusion: All these results contribute to an improvement in the criticality index and a safe application of this system on transportation of persons.