Superconducting Maglev Research Articles

Levitation performance of the magnetized bulk high- Tc superconducting magnet with different trapped fields

To a high- T c superconducting (HTS) maglev system which needs large levitation force density, the magnetized bulk high- T c superconductor (HTSC) magnet is a good candidate because it can supply additional repulsive or attractive force above a permanent magnet guideway (PMG). Because the induced supercurrent within a magnetized bulk HTSC is the key parameter for the levitation performance, and it is sensitive to the magnetizing process and field, so the magnetized bulk HTSC magnets with different magnetizing processes had various levitation performances, not only the force magnitude, but also its force relaxation characteristics. Furthermore, the distribution and configuration of the induced supercurrent are also important factor to decide the levitation performance, especially the force relaxation characteristics. This article experimentally investigates the influences of different magnetizing processes and trapped fields on the levitation performance of a magnetized bulk HTSC magnet with smaller size than the magnetic inter-pole distance of PMG, and the obtained results are qualitatively analyzed by the Critical State Model. The test results and analyses of this article are useful for the suitable choice and optimal design of magnetized bulk HTSC magnets.

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.

Influence of the Trapped Field on the Levitation Performance of the Magnetized Bulk High-T c Superconductor

A magnetized bulk high-Tc superconductor (HTSC) magnet is a good candidate to improve the levitation performance of the high-Tc superconducting (HTS) maglev system. Compared with the unmagnetized bulk HTSC, the magnetized bulk HTSC magnet can supply stronger levitation or guidance force above a permanent magnet guideway (PMG). Different from the permanent magnet, the magnetic field of a magnetized bulk HTSC magnet is sustained by the induced superconducting current produced during the magnetizing process. Given that the induced superconducting current within the magnetized bulk HTSC magnet is very sensitive to the magnetic field, the levitation performance of the magnetized bulk HTSC magnet is directly related to its own trapped field and the magnetic field of the PMG. This article discusses the influence of trapped and external magnetic fields on the levitation performance of a magnetized bulk HTSC magnet by experiments, and the Critical State Model is used to analyze the test results. The analyses and conclusions of this article are useful for the application of magnetized bulk HTSC magnet in practical HTS maglev systems.

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.

Oscillation Characteristics of Levitation Force of YBCO Bulk Exposed to AC Magnetic Field above NdFeB Guideway

In the present High Temperature Superconducting (HTS) maglev vehicle system, the nonuniformity of the magnetic field along the movement direction above the NdFeB guideway is inevitable due to the assembly error and inhomogeneity of the material property of the NdFeB magnet. In order to investigate the influence of the nonuniformity on the levitation performance of the HTS bulk, the experiment involved an electromagnet, which is supplying AC current to simulate the nonuniformity of the external magnetic field. The levitation force of the HTS bulk is measured when applying AC current on the electromagnet coils. The results indicate that the levitation force abruptly changes and oscillates after applying AC external magnetic field. The effect of the amplitude of the AC magnetic field on the levitation force is studied; the result shows that the oscillation amplitude of the levitation force increases with the amplitude of the AC external magnetic field and is independent of the Field Cooling Height (FCH) of the bulk.

Levitation Performance of Bulk High Temperature Superconductor Above the Permanent Magnet Guideway at Different Temperatures

The levitation performance of a high temperature superconducting (HTS) Maglev system was investigated at different temperatures for HTS Maglev vehicle application. Using a cryogenic measurement system, we studied the effects of the HTS’s temperatures and the HTS’s field-cooling heights (FCHs) on the levitation force and its force density by applying a two-pole Halbach array’s permanent magnet guideway (PMG) at different temperatures. Results show that the levitation force is not only dependent on the temperature but also dependent on the original FCH. The effect of the temperature on the levitation force is considerably minute in low FCH. However, it was confirmed that the levitation force of HTS is larger at a lower temperature than at a higher temperature in high FCHs. Moreover, by applying the temperature of 60 K, the levitation force density of the system can be increased by 65% and 57.3% compared to the force density at 77 K in 35 mm and 40 mm FCHs. Hence, more magnetic energy at a low temperature area and high FCH can be utilized. The advancement of Maglev system’s performance will directly promote the development of HTS Maglev application and is helpful for the further HTS Maglev vehicle.

Design and Structural Analysis of Two Kinds of Liquid Nitrogen Vessel for High Temperature Superconductor Maglev Vehicle

<para xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> A double-shell rectangular-shape liquid nitrogen vessel with thin wall for high temperature superconductor (HTS) Maglev vehicle is described in this paper. Its severe working conditions, such as sharp low temperature and strong magnetic field, determine its special structure. Three dimensional finite element analysis (FEA) using dimensions of the vessel, especially thickness of the walls, the largest levitation force obtained from the former experimental results, properties of metallic and nonmetallic material as design parameters was conducted to obtain optimal structure of the vessel. FEA of austenitic stainless steel 0Cr18Ni9Ti metallic vessel and polymer composite (PC) nonmetallic vessel with thin wall were performed. Comparison of the calculation results of two kinds of vessel shows that PC nonmetallic vessel can well satisfy the requirements of HTS Maglev vehicle. Furthermore, PC nonmetallic vessel has many advantages such as no eddy current loss, lesser total weight and lower cost, etc. Due to the finite element model (FEM) being simplified, the results of the numerical calculation should be verified by experimental results. Whereas, FEA as a powerful tool to predict stress and deformation of the model, it can guide and optimize the design of the liquid nitrogen vessel effectively. </para>

Levitation Force Transition of High-Tc Superconducting Bulks in Varying External Magnetic Field

In practical application of a High-Tc Superconducting (HTS) maglev vehicle, the onboard HTS bulks are inevitably exposed to a varying inhomogeneous field due to present processing and assembling technology of the permanent magnetic guideway (PMG). To explore the influence on the levitation forces of YBa2Cu3O7-x bulk samples in such changing external magnetic field due to different traveling speeds, we experimentally investigated the general transition of said levitation force under such varying external field simulated by a spinning circular PMG. The force waves attenuated in accordance to the varying of the applied field dependent on the PMG's rotating speed: attenuating when speeding up and rising slightly when speeding down. This observed phenomenon is of great importance in design and application of the HTS maglev system.

Hybrid Levitation While Incorporating YBCO Bulks With DC Coil

In order to improve the levitation performance of high temperature superconducting (HTS) maglev, a DC coil was winded around double-layered YBCO bulks to enable the controllability of the levitation system. The hybrid levitation forces and guidance forces were studied. It was found that by increasing the repelling force between the DC coil and permanent magnetic guideway (PMG), the levitation force had been remarkably improve; however, the stability of the system was gradually crumbled. Therefore, DC coil could be used to improve the levitation force within the permission of stability. On the other hand, within the permission of the levitation force declination, increase the attraction force between DC coil and PMG could enhance the guidance force. The performance of the YBCO bulks was also affected by the existence of the DC coil, which will be discussed from Bean's critical state model.

Influence of Horizontal Vibrations on the Lateral Stability of Bulk High Temperature Superconductors

The dynamic responses and levitation forces of a high temperature superconducting (HTS) maglev vehicle system were investigated through the propagation simulation of seismic waves by a horizontal vibration platform. The HTS maglev vehicle system consisted of an array of seven YBaCuO high temperature superconductor (HTSC) bulk samples suspended above a permanent magnet guideway. Excitation frequencies of 0 to 60 Hz and excitation amplitudes of 1 to 3 mm were used to measure the HTS bulks characteristics in the time domain and horizontal displacements under horizontal vibrations. Results show that lateral stability and levitation performance is correlated to the excitation amplitude and the excitation frequency at the resonance frequency 5 Hz. This in turn is helpful towards the application of HTS maglev vehicles in the future.

An Asymmetrical Permanent Magnet Guideway Design for the High Temperature Superconducting Maglev Curve

An asymmetrical permanent magnet guideway (PMG) design is considered for the high temperature superconducting (HTS) Maglev during traveling on a curved path. This translationally asymmetrical PMG design can produce a better guidance performance, which cannot be provided by the common translationally symmetrical PMG design. The additional guidance improvement is attributed to its asymmetrical magnetic field distribution. The outside part of the asymmetrical PMG has more magnetic material than the inside part, so that the outside magnetic field density is enhanced or becomes a multi-pole distribution. These two effects result in a larger guidance force and a better curve negotiation ability. Above the asymmetrical curved PMG, the HTS Maglev vehicle system can overcome larger centrifugal forces and run with a smaller or even zero lateral displacement. Moreover, this asymmetrical PMG design is helpful to realize the “straight line to curve to straight line” running environment. The improvement effect and running feasibility of the asymmetrical PMG is calculated and proven for future use in HTS Maglev curves.

Dynamic Simulation of High Temperature Superconductors Above a Spinning Circular Permanent Magnetic Guideway

Before a high temperature superconducting (HTS) magnetic levitation (Maglev) vehicle system can be fully applied and operational, the study of its dynamic characteristics is necessary. With the developed HTS Maglev dynamic measurement system (SCML-03), with a circular permanent magnet guideway (PMG) of 1.5 m in diameter, the vehicle’s translational motion above a PMG can be effectively simulated with the PMG allowed to rotate freely. Levitation force measurements of a high temperature superconductor (HTSC) array of seven YBa2Cu3O7−x bulks were carried out above regular (linear) and a simulated (circular) PMG. The levitation force above a linear PMG segment and a circular PMG segment in the static state is found to be in good agreement with each other. The levitation force in the dynamic state is found to slowly attenuate since the presence of a rotating circular PMG below the HTS array is found to be analogous to the application of an AC external magnetic field.

Mechanical Vibration Experiment of Superconducting Magnet

The resonance modes of the on-board superconducting magnet for the JR Maglev system actually obtained at the durability test were two (propulsion and levitation modes). To reduce the durability test period of the specimen by half, it was investigated in this study how those two resonance modes were simultaneously reproduced. It appears that those two resonance modes are simultaneously reproducible if the three accelerating points to reproduce its levitation mode are used, and if proper beams to shift the resonance frequencies of its propulsion and levitation modes are added.

Influence of Vertical Vibrations on an Array of Bulk HTSC Above the Permanent Magnet Guideway

The dynamic response of high-temperature superconducting (HTS) maglev vehicle system, which consists of a high-temperature superconductor (HTSC) array of seven YBa2Cu3O7−x bulks above permanent magnet guideway (PMG), was investigated experimentally. The dynamic stiffness and displacements and the levitation force of the bulk HTSCs were investigated as function of the external excitation amplitudes in the range of 1–4 mm and frequencies in the range of 1–400 Hz. The levitation force and the resonance frequency and the dynamic stiffness of the bulk HTSCs are correlative to reduce with the excitation frequency lower than 30 Hz and the applied excitation amplitude higher than 3 mm due to the energy loss. However, the experimental results show the reduction occurred in the first several cycles, which proves that the array of the bulk HTSCs can sustain the external excitation vibration in the vertical direction due to its strong dynamic stiffness. The experimental results are helpful in the application of the HTS maglev vehicle in the future.

A Method to Increase the Lateral Reversible Region of Bulk YBCO Above a Permanent Magnet Guideway

Lateral reversible region of the bulk high-Tc superconductor (HTSC) above the permanent magnet guideway (PMG) is a key parameter for the high-Tc superconducting (HTS) maglev system. The lateral stability and guidance force are proportional to the width of the lateral reversible region. When the lateral displacement of the bulk HTSC exceeds the reversible region, the maglev system will return to a new lateral equilibrium position. The method with the use of pre-displacement can successfully increases the lateral reversible region of the bulk HTSC. By the correct choice of the maximum lateral offset and a new starting point, the instability of flux motion can be suppressed. Unsuitable usage of this method will cause the intersection of guidance force and reduce the reversible region. Analyses based on the magnetizing history and pinning metamorphoses well explain the experimental results. Difference between this method and the pre-load method is also discussed in this article.

Flux Concentrator Optimization of PMG for High-Temperature Superconducting Maglev Vehicle System

The permanent magnetic guideway (PMG) composed of permanent magnet (PM) and steel is developed under flux concentration principle, which is the crucial component of high-temperature superconducting (HTS) maglev vehicle system. Optimum PMG design is an effective way to increase levitation force and associated stiffness for improving the load capability of HTS maglev vehicle. In order to realize higher vertical field component B z in upper surface, three PMG demonstrators with three different forms of flux concentrator are fabricated with same volume of magnet. The levitation performances of onboard HTS bulks array over them are studied. The experimental results indicate that the PMG with a permanent magnet as the flux concentrator would produce biggest levitation force, levitation stiffness and trapped flux when interacting with HTS superconductor.

3D Modeling Permanent Magnet Guideway for High Temperature Superconducting Maglev Vehicle Application

A three-dimensional analytical method is proposed to model the permanent magnet guideway (PMG) involved in the high-temperature superconducting (HTS) maglev vehicle system, and with this analytical method, the non-uniformity of magnetic field along the longitudinal direction of the PMG due to the existent gap between the adjacent permanent magnet (PM) can be taken into account in the simulation of the HTS maglev vehicle system. The analytical expressions for two rectangular PM with different magnetization directions are deduced from the Biot–Savart’s law. The 3D modeling of the PMG is validated from the four aspects, i.e., the comparison of the measurement and calculation value of the magnetic field; the magnetic field contour of the PMG; the comparison of the 3D method results with the 2D method; and the comparison of the results from the present 3D analytical model and previous finite element software. Currently, using the 3D analytical model, we have proposed a 3D method to numerically investigate the HTS magnetic levitation/suspension system with bulk high-temperature superconductor (HTSC).

Recent Development of High Temperature Superconducting Maglev System in China

After the first man-loading high temperature superconducting (HTS) Maglev demonstration had been tested successfully years ago, its future application attracts more and more researchers and engineers. This paper reviews the recent development of HTS Maglev system in China. In the past seven years, quasi-static forces, dynamic characteristics and running performances have been studied by three self-developed HTS maglev measurement systems and 11-ch vibration measurement apparatus. Some practical problems are considered in details for further engineering application of HTS Maglev train, such as running along the forward direction with inhomogeneous magnetic field, construction cost estimation, propulsion optimization, and so on. On the other hand, a systematic method is introduced to analyze or optimize the force interaction between bulk high temperature superconductor and permanent magnetic guideway. Primary running parameters and data are obtained for the safety design of future HTS Maglev system. Furthermore, a low-mid speed HTS Maglev test line is blueprinted with a maximum speed of 100 km/h, which will be the first step of practical HTS Maglev engineering application.

Performance Improvement of High Temperature Superconducting Maglev System by Eddy Current Damper

<para xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> An indirect method of incorporating eddy current damper in the high temperature superconducting (HTS) Maglev vehicle system is presented in the paper. Effect of eddy current damper with different shapes and fixed positions are studied in a seven-bulk YBaCuO levitation system over the permanent magnet guideway (PMG). Similarly to the direct optimizations of the HTS-PMG system, this method is able to improve the damping performance of the HTS Maglev vehicle system without changing other performance. On the other hand, the drag force caused by eddy current damper has been discussed and analysed, which is regarded as a possible technical obstacle for the practical HTS Maglev application. Here, it is concluded that the drag effect can be solved by the propulsion tool. So, the incorporation method of eddy current damper can be one effective improvement method for the practical HTS Maglev application in the future. </para>

Performance Advances of HTS Maglev Vehicle System in Three Essential Aspects

In order to put the practice of high temperature superconducting (HTS) Maglev vehicle technology into people's life, the interaction between high temperature superconductor (HTSC) and permanent magnet guideway (PMG) as the basic model of HTS Maglev vehicle was carefully investigated and enhanced from three essential aspects, i.e., bulk HTSC material, PMG field and bulk HTSC magnetization. The maglev experiments were performed with three kinds of bulk HTSC materials, two kinds of PMGs and two kinds of magnetization methods. It is found that three aspects are all very effective to improve the levitation capability and lateral stability. With better bulk material, more reasonable PMG configuration and magnetization method, the performance of HTS Maglev vehicle system will be greatly advanced and closer to an economical and practical level.