Levitation Force Relaxation of HTS YBCO Bulk under Load

The loading capacity of the high temperature superconducting (HTS) maglev vehicle is closely relative to the maglev characteristics of the HTS bulk under the load. The investigation of the characteristics is necessary for the application of the HTS maglev vehicle. In our previous work, it was found that the levitation force relaxation increased with the increase of the reloading. In this paper, in terms of a HTS maglev system composed of the permanent magnetic guideway (PMG) and a HTS YBCO bulk, the levitation force relaxation under different loads is investigated by the numerical calculation and the experiment. It is found that the normalized relaxation rate of the levitation force increased with the increase of the load. The influence of the load on the current density distribution is also discussed in this paper. This work might be helpful for the research of the loading capacity of the HTS maglev vehicle.      

Influence of AC External Magnetic Field on the Levitation Force Relaxation of HTS Bulk Above NdFeB Guideway

In the present High-Temperature Superconducting (HTS) maglev vehicle system, the air gaps between the adjacent permanent magnets make the magnetic fields above the NdFeB guideway non-uniform. So one is required to study the characteristics of levitation force of the HTS bulk influenced by non-uniform fields. In this paper, we have studied the characteristics of the levitation force relaxation by an experiment in which the AC external magnetic field generated by an electromagnet is used to simulate the time-varying external magnetic field caused by the inhomogeneity of the NdFeB guideway. From the experiment results, it is found that the levitation force is attenuated with the application of the AC external magnetic field, and the decay is increased with the amplitude of the AC magnetic field, but the decay is almost independent of the frequency of the AC magnetic field.     

Influence of Work Height on Guidance Force Decay of HTS Bulk Exposed to AC Magnetic Field Perturbation in a Maglev Vehicle System

Bulk superconductors have great potential for various engineering applications, especially in superconducting maglev vehicle systems using high-temperature superconducting bulks. In such a system, the HTS bulks were always exposed to AC external magnetic field, which was generated by the inhomogeneous surface magnetic field of the NdFeB guideway. In our previous work, it was observed that the guidance force of the YBCO bulk over the NdFdB guideway used in the high-temperature superconducting maglev vehicle system was decayed by the application of the AC external magnetic field. In this paper, we investigate the influence of the work height on the guidance force decay of HTS bulk exposed to an AC field perturbation in the maglev vehicle system and try to adopt a method to suppress the decay. From the experimental results, it was found that the decay rate of the guidance force was smaller at higher work height in the case of the same field-cooled height. So we could suppress the guidance force decay of HTS bulk exposed to AC external magnetic field perturbation in the maglev vehicle system by increasing the work height of the bulk.     

Influence of Thermal Conductivity on Guidance Force Decay of HTS Bulk Exposed to AC Magnetic Field Perturbation in a Maglev Vehicle System

Bulk superconductors have great potential for various engineering applications, especially in a high-temperature superconducting (HTS) maglev vehicle system. In the vehicle system, the stable levitation can be achieved without any complex control system owed to the pinning effect of the bulks. However, the HTS bulks in the vehicle system were always exposed to the time-varying external magnetic field, which was generated by the inhomogeneous surface magnetic field of the NdFeB guideway. In our previous work, we studied the guidance force decay characteristics of the YBCO bulk over the NdFdB guideway used in the HTS maglev vehicle system by an experiment in which the AC external magnetic field generated by an electromagnet was used to simulate the time-varying external magnetic field caused by the inhomogeneity of the guideway, and calculated the guidance force decay as a function of time based on an analytic model. In this paper, we investigated the influence of thermal conductivity on the guidance force decay of HTS bulk exposed to AC field perturbation in the maglev vehicle system and tried to adopt a method to suppress the decay. From the results, it was found that the guidance force decay rate was higher for the bulk with the lower thermal conductivity. So, we could reduce the guidance force decay of the HTS bulk exposed to the AC external magnetic field perturbation in the maglev vehicle system by improving the thermal conductance of the bulks.     

Influence of Critical Current Density on Guidance Force Decay of HTS Bulk Exposed to AC Magnetic Field Perturbation in a Maglev Vehicle System

Superconducting maglev vehicle is one of the most promising applications of HTS bulks. In such a system, the HTS bulks are always exposed to AC external magnetic field, which is generated by the inhomogeneous surface magnetic field of the NdFeB guideway. In our previous work, we studied the guidance force decay of the YBCO bulk over the NdFdB guideway used in the High-temperature superconducting maglev vehicle system with the application of the AC external magnetic field, and calculated the guidance force decay as a function of time based on an analytic model. In this paper, we investigated the influence of the critical current density on the guidance force decay of HTS bulk exposed to AC field perturbation in the maglev vehicle system and try to adopt a method to suppress the decay. From the results, it was found that the guidance force decay rate was higher for the bulk with lower critical current density. Therefore, we could suppress the guidance force decay of HTS bulk exposed to AC external magnetic field perturbation in the maglev vehicle system by improving critical current density of the bulk.     

Influence of Off-Centre Operation on the Performance of HTS Maglev

Owing to instinctive self-stable levitation characteristics, high-temperature superconducting (HTS) maglev using bulk high-temperature superconductors attracts more and more attention from scientists and engineers around the world. In this paper, the levitation force relaxation and guidance force characteristics of a Y–Ba–Cu–O levitation unit with different eccentric distances (EDs) off the center of the permanent magnet guideway were experimentally investigated under field-cooling (FC) conditions. Experimental results indicate that the levitation force slightly increases at small EDs firstly, but degrades with further increasing of EDs. However, the maximum guidance force and its stiffness exhibit enhancement in moderate ED range. The results demonstrate that a properly designed initial FC eccentric distance is important for the practical applications of HTS maglev according to specific requirements like running in curve lines.     

Study of the Dynamics of Vortex Structures in Bulk HTS with Levitation Techniques

The discovery of high temperature superconductors (HTS) has led to understanding that, in order to explain and utilize the phenomenon, completely new physical approaches should be introduced at all scales: microscopic, mesoscopic, macroscopic. Leaving first two scales beyond the scope of the present paper we focus in the upper limit of the last one, the study of the magnetic flux dynamics in HTS bulks - the dynamics of the 'compact vortex structures'. New experimental approaches to investigation of HTS bulks using levitation techniques, which have been elaborated during last years to effectively explore the subject, as well as the new fundamental and applied results obtained therefrom are overviewed here.     

Correlations Between Magnetic Flux and Levitation Force of HTS Bulk Above a Permanent Magnet Guideway

In order to clarify the correlations between magnetic flux and levitation force of the high-temperature superconducting (HTS) bulk, we measured the magnetic flux density on bottom and top surfaces of a bulk superconductor while vertically moving above a permanent magnet guideway (PMG). The levitation force of the bulk superconductor was measured simultaneously. In this study, the HTS bulk was moved down and up for three times between field-cooling position and working position above the PMG, followed by a relaxation measurement of 300 s at the minimum height position. During the whole processes, the magnetic flux density and levitation force of the bulk superconductor were recorded and collected by a multipoint magnetic field measurement platform and a self-developed maglev measurement system, respectively. The magnetic flux density on the bottom surface reflected the induced field in the superconductor bulk, while on the top, it reveals the penetrated magnetic flux. The results show that the magnetic flux density and levitation force of the bulk superconductor are in direct correlation from the viewpoint of inner supercurrent. In general, this work is instructive for understanding the connection of the magnetic flux density, the inner current density and the levitation behavior of HTS bulk employed in a maglev system. Meanwhile, this magnetic flux density measurement method has enriched present experimental evaluation methods of maglev system.     

Influence of the Vertical Inclination of Permanent Magnet Guideway on Levitation Characteristics of Hts Maglev System

In the application of high temperature superconducting (HTS) magnetic levitation (maglev) system under vertical inclination of permanent magnetic guideway (PMG), the component of the total weight of levitation body above the PMG will be changed. Therefore, the influence of the vertical inclination of PMG on levitation characteristics of HTS maglev system cannot be ignored, such as the levitation gap, the levitation force, guidance force and driving force of the linear motor. In order to investigate the influence of the vertical inclination angle on levitation characteristics of the HTS maglev system, a HTS maglev launch platform has been designed and fabricated for the investigation the influence of vertical inclination angle between the range of 0° and 18° on the levitation and guidance and driving force parameters of the HTS maglev launch platform. Experimental results show that the levitation gap was the main levitation characteristic for HTS maglev system under vertical inclination of PMG, which increased with increment of the vertical inclination angle. However, the levitation force, and the driving force of the linear motor decreased. The guidance force could not be influenced by the increment of levitation gap. The experimental results are helpful toward improving the running performance of the HTS Maglev launch system.     

Levitation Force Relaxation of HTS Bulk above NdFeB Guideways at Different Approaching Speeds

The zero-field cooling levitation force relaxation of the YBCO bulk above two types of NdFeB guideways, which were used in the high-temperature superconducting maglev vehicle system, was studied experimentally when the bulk moved towards the guideways at different speeds. In this experiment, a sample with the diameter of 50 mm and thickness of 15 mm was used; the time range in the relaxation measurements was from 0 s to 200 s. As a result, a nearly linear logarithmic decay of the levitation forces with time was observed. It was found that the influence of the approaching speeds on the levitation force relaxation is different, and that the levitation force decay is closely related to the guideway structures. Based on the monopole peak PMG, the approaching speeds will influence more the levitation force decay than the multipole Halbach. So the maglev vehicle above mutipole Halbach structure PMG will work more stably than that above the monopole peak PMG.      

Numerical Study of the Curve Route Levitation Performance of the HTS Bulk over NdFeB Guideway

The passive levitation has a self-adjust characteristic to adapt to environmental changes. Levitation Height (LH) or Lateral Displacements (LD) of the high-temperature superconducting (HTS) Maglev vehicle, running over Permanent Guideway (PMG), will change respectively or synchronously due to some external reasons, which caused the vehicle move a certain distance in vertical direction (Y direction) or horizontal direction (X direction) according to a line space route curve along Y or X direction, or random route lying in a XY plane which is perpendicular to the vehicle running direction (Z direction) corresponding to a complicated space route curve. In these cases, how are the levitation performances of the HTS bulk? From a simplest space line route, this paper studied computationally the curve route levitation performance of the HTS bulk which is subject to a PMG applied field. Results show that the change of the levitation and guidance force is different when the HTS bulk moved along line space route. This provides important scientific theories for the numerical simulation of HTS Maglev vehicle.     

Measurement Method to Evaluate the Practical Levitation Force of Onboard Bulk Superconductor in the High-Temperature Superconducting Maglev Vehicle System

As the basic parameter in the design of high-temperature superconducting (HTS) magnet levitation (maglev) vehicle system, the levitation force data are usually obtained by experiments, so a reliable measurement method is needed to know the practical levitation force of onboard bulk superconductor. Considering in the actual operation the vehicle will experience some small vertical or lateral movements, especially during the passenger going on or off the vehicle, the usual measurement method for levitation force, in which force with gap and force relaxation are measured, cannot be able to predict the levitation force change due to the vertical or lateral movements. So a measurement method is presented regarding effects of force with gap, relaxation, vertical and lateral movements. Compared with a former measurement method, the presented method may support more reliable levitation force data for the HTS maglev vehicle design.     

Enhanced Maglev Performance by Field Cooling for HTS Maglev System in Curve Negotiation

In the practical operation of high-temperature superconducting (HTS) maglev system, the problem of curve negotiation cannot be neglected. During the process of going through curve path, the maglev vehicle would laterally deviate from the center of the permanent magnet guideway (PMG) because of centrifugal forces. To explore the performance variation of the maglev system in this process, the electromagnetic forces (levitation force and guidance force) of a HTS bulk levitation unit were experimentally investigated by different eccentric distances (EDs). The ED is emulated by laterally moving the levitation unit relative to the PMG. Experimental result shows that in field-cooling (FC) conditions, the levitation force generally shows a increase tendency with the growing EDs, while it keeps decreasing in zero-field-cooling (ZFC) conditions. And, the levitation force with large EDs in the FC condition is larger than that in the ZFC condition. The guidance force is enhanced in both conditions within ED of 15 mm, and in FC condition, the force is larger than the case of ZFC. Comparing the above two important magnetic force results, the FC condition is recommended for the safe operation of the HTSn system in curve negotiation.     

Influence of the Air Gap between Adjacent Permanent Magnets on the Performance of NdFeB Guideway for HTS Maglev System

For the permanent magnet guideway (PMG) of the high temperature superconducting (HTS) magnetic levitation (Maglev) vehicle system, there should be many air gaps between two adjacent permanent magnets by connecting, which may fluctuate magnetic field in the propulsion direction of the vehicle. A three-dimensional (3D) model of a PMG is built up using FLUX 3D software. The magnetic field density of an NdFeB PMG is measured and simulated by 3D and 2D models. Comparison among their results indicate that the simulation results of the 3D model agree better with the measuring results than that of the 2D model, and thus the 3D model is more suitable to describe the PMG. By the model, the influence of the air gap on the uneven of the magnetic field density in the propulsion direction is studied. It is found that the magnetic field 15 mm above the PMG is roughly even in the propulsion direction, although the magnetic field at 2 mm is not even. Since the working height 15 mm is a sensitivity parameter for the onboard high temperature superconductor (HTSC), the levitation force at working height 15 mm above PMG is measured, which indicates that the influence of the air gap on the levitation force is very small so as to be ignored in the quasi-static state.     

Numerical Evaluation of Levitation Force Oscillation of HTS Bulk Exposed to AC Magnetic Field over NdFeB Guideway

The levitation force of the YBCO bulk over an NdFeB guideway used in the high-temperature superconducting (HTS) maglev vehicle system is oscillated by the application of the AC external magnetic field. In our previous work, we interpreted that the oscillation is due to the shielding current fluctuation caused by fluctuant external magnetic field. In this paper, based on the Bean model, an analytical model is adopted to evaluate the levitation force. Comparing with the experimental results, the calculated results show good matching. The model can reveal the oscillation characteristics of the levitation force of HTS bulk which is being exposed to AC external magnetic field. Therefore, the levitation force oscillation of the HTS bulk in the maglev vehicle system can be evaluated by this numerical method.     

Levitation Forces Acting on an HTS Sample in the Field of a Permanent Magnet

Journal of Superconductivity and Novel Magnetism - Using the Monte Carlo method, the vertical z-component of levitation force acting on a thin HTS film in a field simulating the inhomogeneous field...     

高速磁浮列车悬浮间隙传感器的研究

针对高速磁浮列车悬浮间隙传感器所面临的齿槽纹波效应、温度环境以及电磁干扰等特殊问题,分别从线圈设计、电路模型分析、软件补偿及抗电磁干扰等方面进行了研究.通过计算等效电感,设计了中间下陷形式的立体结构的检测线圈,使传感器在额定悬浮间隙下最终输出的纹波误差小于±0.4 mm;通过设计差分电路结构和温度修正表,解决了传感器温度漂移问题;通过设计8字结构线圈和电磁干扰滤波器,使传感器通过了电磁兼容测试.     

Numerical Study of the Speed-Related Behavior of the Magnetic Force in the HTS Maglev System Based on a 3-D Model

Based on the 3-D model, we recently proposed to investigate numerically the performance of the HTS maglev system. The speed-related behavior of this kind of maglev system is further studied in this article. The 3-D model is firstly briefly introduced: the 3-D governing equations are established with current vector potential (T) as the state variable, and the special anisotropic behavior and the nonlinear E?CJ characteristic of the HTS were taken into account by an elliptical model and power-law model, respectively. Using a translational symmetry levitation system, which is composed of a rectangular HTS and a permanent magnet guideway (PMG) as an example, the speed-related behavior of the magnetic force in three different cases??i.e., the levitation force (LF) versus gap relation under the vertical movement, the time evolution of the LF, the guidance force (GF) versus lateral displacement relation under the transverse movement??are investigated. The result indicates that, with the increase of the speed, both the LF and GF increase but the rate of increase is reduced and finally saturates when the speed is large enough. We also find that the commonly used speed of 1 mm/s to investigate the magnetic force of the bulk HTS in the experiment is reasonable because both the LF and GF tend to saturate at this speed. For the time evolution study of the LF, although the peak value of the LF is largest when the speed is largest, the LF decay in the relaxed process is most serious, and consequently the final LF at different speeds is almost identical after relaxation. Therefore, the magnetic force cannot be enhanced by simply increasing the speed in the practical application.     

The Influence on Levitation Force of the Bulk HTSC Above a Permanent Magnet Guideway Operating Dive-Lift Movement with Different Angles

In practical applications, the operating of accelerating or decelerating inevitably happens in the high temperature superconducting (HTS) Maglev train. For the further research of the Maglev properties of bulk high temperature superconductor (HTSC) above a permanent magnet guideway (PMG), by moving a fixed vertical distance, this paper studies the influence on levitation force of the bulk HTSC operating dive-lift movement with different angles. Results show that with the angle increasing, the maximal levitation force decreases when the levitation gap is about 10?mm and the hysteresis is increasing. The hysteresis reaches the largest at first time of back and forth movement, and with the operating times increasing; the hysteresis is almost the same case in the following times of back and forth movements.     

Generation of Bulk HTS with Doped Tungstates

Doped tungstates exhibit superconductivity as indicated to occur mainly at the surface of the WO₃ grains present. To generate bulk 3D superconducting material of doped tungstates, it is proposed to employ the recently discovered UV-generated synthesis of complex oxides from mixed simple oxides by illuminating the mixture with ultraviolet light at modest temperatures, as found in Shengelaya’s group in Tbilisi, and to generate a percolating 3D network of 2D superconducting sheets using the smallest basis oxides as the starting material. The latter procedure was demonstrated recently to be very effective in a collaboration with the present author (Daraselia et al., J. Appl. Phys. 121, 145104, 2017). If this proposition is successful, it would establish the doped tungstates as a second group of HTS besides the copper oxides that could be chosen for certain applications.