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• Design permanent magnet for high-temperature superconducting Maglev systems. • Analyze the demagnetization characteristics of guideways at high temperatures. • Choose the Halbach-type guideway with better performance for detailed optimization. High-temperature superconducting (HTS) pinning Maglev systems are advantageous due to their ability to achieve large-scale passive-stabilized levitation. Elevated temperatures can lead to a reduction in the magnetic characteristics of the permanent magnet guideway (PMG), which may pose a risk to the safe functioning of HTS Maglev trains. In order to guarantee the secure and dependable functioning of HTS Maglev trains, it is necessary to augment the high-temperature stability of the PMG. This study involves simulating the high-temperature stability of present PMGs and developing a new PMG that exhibits greater performance. Magnetic field simulation is employed to compute the demagnetization of permanent magnets (PMs) in several typical PMGs, encompassing both reversible and irreversible scenarios, in order to examine the factors contributing to demagnetization and evaluate the thermal stability of the PMGs at elevated temperatures. The grade, size, and magnetization direction of the Halbach-type PMG are subsequently optimized and compared to the original Halbach-type PMG. Following this, ideas for further optimization are provided. The optimized Halbach-type PMG reduces the overall decay ratio of the highest magnetic flux density B z by 5.77% compared to the existing Halbach-type PMG. Additionally, the irreversible decay ratio is decreased by 6.13% at 85 ℃. The levitation force decay ratio on the HTS bulks above the optimized Halbach-type PMG is decreased by 8.11% compared to the existing Halbach-type PMG. Additionally, the irreversible decay ratio is reduced by 9% at 85 ℃. This study provides valuable insights for enhancing the efficiency and performance of PMGs and HTS Maglev trains over extended periods of operation. [ABSTRACT FROM AUTHOR]

• The stability and reliability of the battery unit against the over current fault in charging process can be further improved. • The charge voltage fluctuation of the battery unit can be also compensated by using the proposed protection strategy. • It is a new application field of YBCO thin film in battery unit, to limit the over current and compensate the voltage drop. This paper proposes a novel over current protection strategy based on YBa 2 Cu 3 O 7-x (YBCO) thin film current limiter, to improve the over current stability of the battery unit in superconducting magnetic energy storage (SMES)-battery hybrid energy storage system (HESS) during charging process. The conventional over current protection strategy for battery unit is based on cutting off the operation of the battery unit to remove the fault. Especially, during the charging process, once the battery unit circuit is cut off, the stability and reliability of the HESS will be also reduced. Hence, considering the features of the YBCO thin film in both superconducting state and quench state, it can be deployed as the over current limiter, to keep the stability of the battery unit against the over current fault during the charging process. In this paper, we designed and fabricated the YBCO thin film over current limiter, meanwhile, the preliminary verification experiment was carried out in our laboratory. It can be found from the experimental results that the over current in battery unit can be limited effectively by its quench resistance without cutting off the whole circuit. Besides, the charge voltage fluctuation of the battery unit can be also compensated by using the proposed protection strategy. Thus, the stability and reliability of the battery unit against the over current fault in charging process can be further improved. [ABSTRACT FROM AUTHOR]

• Damping ratio is related to the amplitude and static levitation height. • Damping differs on both sides of the vibration equilibrium point. • Calculating system damping through the cross-correlation function. • Eddy current damping of conductive shell couples with the hysteresis damping. High-temperature superconducting (HTS) pinning maglev has achieved rapid development in recent decades. The levitation system of the HTS pinning maglev is mainly composed of Dewar with built-in HTS bulks and permanent magnet guideway (PMG). For a maglev transportation system, damping is important for vibration attenuation, and the inherent damping characteristics of the HTS pinning maglev system have not been evaluated clearly. In this paper, the damping characteristics of the HTS pinning maglev system are analyzed through experiments and simulations. Experiments are conducted to measure the dynamic responses of the system under free and forced vibrations. The logarithmic envelope method is used to evaluate the system damping under free vibration. The cross-correlation function is utilized to obtain the phase difference between the system vibration signal and excitation signal, and then calculate the system damping under forced vibration conditions. In addition, a two-dimensional finite element model including HTS bulks, PMG, and Dewar conductive shells is established to evaluate the damping force generated by each component during system vibrations. The additional eddy current damping of the conductive Dewar shell is considered and analyzed. Finally, from the perspective of system damping and thermal stability of HTS bulks, suggestions for selecting Dewar shell materials are proposed. [ABSTRACT FROM AUTHOR]

• Based on H - ϕ formulation combined with moving mesh to establish full 3D models. • Using Halbach array rotors to improve levitation force and stiffness. • Optimized rotor produces larger area of flux penetration and shielding current. • Superconducting bulks coupled with optimized rotor maintains thermal stability. The superconducting flywheel system exploiting the magnetic coupling between the bulk high temperature superconductors (HTSs) and permanent magnets (PMs) exhibits excellent performance of self-stable levitation, and is promising for power applications. In this paper, we use the H - ϕ formulation combined with moving mesh to establish a full 3D model for the thrust type and journal type bearings in the HTS flywheel system. We then proposed different Halbach schemes to enhance the magnetic flux density of the rotor and thus the coupling, and investigated the levitation force, relaxation characteristics, electromagnetic transient distribution, and temperature characteristics of the bearings. Results show that, under axial zero field-cooled (ZFC) condition, the optimized PM rotor scheme can significantly improve the maximum levitation force and stiffness by 4.0 and 2.3 times respectively for the thrust type bearing, and the maximum levitation force of journal type bearing can be improved by a factor of 5.5. Under the radial ZFC condition, the maximum levitation force and stiffness of the journal type bearing have been increased by 4.9 times and 2.9 times. For the relaxation of both bearings during operation, the optimized PM rotors lead to relatively greater attenuation of levitation force. The proximity of the optimized PM rotors intensifies the magnetic flux movement of the HTS bulks but only brings about a limited temperature rise, and the superconductors still maintain a good low-temperature working environment. This study provides an effective methodology for analyzing the HTS bearing systems and good references for the optimal design of compact HTS flywheel energy storage systems (FESSs). [ABSTRACT FROM AUTHOR]

Superconducting pinning maglev train, with the advantages of heavy self-stable levitation and super-low resistance, is expected to become a high-speed transit in the future. With the increase in speed, the more will the irregularity of the PMG (permanent magnet guideway) affects the safety and comfort of the superconducting pinning maglev train. This paper is based on the PMG of the test line for the first high-speed superconducting pinning maglev engineering prototype train in China, to measure and study the magnetic irregularity of the PMG and its characteristics. Experiments were designed to measure the irregularity with a single Dewar maglev system, which can obtain the equivalent geometric irregularity directly acting on the maglev unit of the vehicle. Firstly, the frequency response function is developed based on previous studies, which can transform the response signal of the Dewar into the irregularity signal of the PMG. Secondly, the velocity and position are measured by image recognition of ground markers. Then, the dynamic signal of the Dewar maglev system moving along the PMG is gained and conversed into equivalent geometric irregularities by the frequency response function. Finally, an equivalent geometric irregularity PSD (power spectral density) function is formed, and it can generate the geometrically random track irregularity for vehicle dynamic simulations. The dynamic simulation result suggests that the superconducting pinning maglev train has the potential for smooth operation at high-speed under the excitation of the current PMG. The studies of this paper can help to understand the irregularity of the PMG further, and the gained PSD function can provide a general reference for the dynamic study of the superconducting pinning maglev train. [ABSTRACT FROM AUTHOR]

The loading capacityand stability of the high temperature superconducting (HTS) maglev system greatly depend on the levitation performance of bulk superconductor. Because of the differences in size and fabricating process of the bulks, there was no unified standard and simple method to evaluate the difference in levitation performance among bulks. In this work, we measured the density of 19 YBaCuO (YBCO) bulk samples in different shapes and sizes while their zero-field cooling levitation force and relaxation over a Halbach NdFeB guideway were studied. The results show a significant correlation between the density and levitation performance of a single YBCO bulk superconductor. For samples with the uniform fabrication process and similar properties, higher density means larger levitation force per unit area and smaller relaxation ratio. This conclusion could serve as a reference for HTS Maglev researchers and engineers quickly selecting YBCO bulk superconductors. [ABSTRACT FROM AUTHOR]

High-temperature superconducting (HTS) magnetic levitation (maglev) has the advantages of low-energy consumption and is environment friendly. This article tried to apply this novel technology to sightseeing vehicles. As the bogie is one of the most important components of the vehicle, a new type of bogie was designed for the need of small-radius curve passing and its dynamic characteristics were evaluated. A 3-D model of a bogie with primary suspension was built. By which, the space utilization of the vehicle can be improved and the passengers will have higher comfort. Then, a dynamic model of the vehicle–bridge coupled system was constructed based on a multibody dynamics software, universal mechanism. The dynamic performance of bogie with and without primary suspension was compared to explore its necessity. The vehicle–bridge dynamic performance was simulated and analyzed under different speeds and curve radii. The results show that the HTS maglev sightseeing vehicle with the bogie with primary suspension has favorable dynamic performance. For higher speeds and smaller curve radius, the vibration response will worsen. This study can provide references for the design and optimization of HTS maglev bogies suitable for small-radius curve passing. [ABSTRACT FROM AUTHOR]

The high-temperature superconducting (HTS) maglev system has great potential to become a new type of rail transit due to its unique self-stabilizing levitation, low noise pollution, and environment-friendly operation. However, previous studies have shown that the damping properties of HTS system are low, and hence, its large-amplitude nonlinear vibration is prone to occur under external interference, which will affect the stability, safety, and comfort of the long-term operation of the maglev vehicle. Therefore, it is necessary to improve the damping performance of HTS maglev system, minimize the impact of vibration on the maglev system, improve the anti-interference ability of the system, and ensure the smoothness and stability of the system. In this work, an eddy current damper (ECD) is designed to suppress the vibration that may occur during the operation of the HTS maglev vehicle; the ECD is placed at the same height as the HTS bulks. And by collecting the displacement and acceleration signals of the HTS levitator, the efficiency of dampers in suppressing vibration with different copper thicknesses under different field cooling heights (FCHs) is analyzed. The experimental results show that the additional ECD can effectively reduce the vibration of the HTS levitator, especially among the resonance frequency range. And when the FCH is set to the commonly used engineering height of 30 mm, the ECD has the highest damping efficiency. The relevant research results in this work provide a possible solution to the problems encountered in the operation of the maglev train in the real scene. [ABSTRACT FROM AUTHOR]

• After long-time heavy load, the levitation force of the YBaCuO bulks changes small. • The dynamic model of HTS maglev vehicle is established in UM software. • The dynamic response of the three vehicles are compared under the same condition. • The HTS maglev vehicle is superior to other vehicles in some dynamic parameters. • The HTS maglev vehicle's dynamic performance has potential advantages in high speed. In order to explore the potential advantages of HTS maglev vehicles, the dynamic response of HTS maglev vehicle-bridge coupling system model under different speeds and track beam spans is calculated by using Universal Mechanism (UM) software, which is further compared with two existing high-speed train systems, the high-speed EMS vehicle and wheel-rail vehicle. Before establishing the dynamic model, first a simplified mathematical model of levitation force of HTS maglev is extracted based on the experimental results of three YBCO bulks on a Halbach permanent magnet guideway (PMG). The results of simulation show that the HTS maglev vehicle can fully meet the requirements of current high-speed railway operation index on the acceleration of car body and its influence on track beam. The comparisons show that HTS maglev vehicle has some advantages over high-speed EMS vehicle and wheel-rail high-speed vehicle, especially in the acceleration of the car body and the impact on the track beam under high-speed operation. This makes a better understanding of the dynamic performance of HTS maglev vehicle, and provides an effective reference for the selection of high-speed railway system types and related indicators in the future. [ABSTRACT FROM AUTHOR]

• HTS thin films have the advantages of low profile characteristics and higher critical current density. Its levitation characteristics have the potential to play as the levitation device to offer the sufficient levitation force in the limited volumes and spaces. • The weak stiffness issue of the HTS superconductors can be improved by photo-etching the meander-lines with carrying DC current in thin film interface. • The double sided YBCO thin film can be employed in the microgravity fields to supply the stable levitation force in the limited space. In this paper, the levitation characteristics of double sided high temperature superconducting (HTS) thin film device is proposed and measured. Based on the unique advantages such as, passive self-stable levitation, higher payload, lower energy consumption, less maintenance cost, etc., HTS-magnetic levitation (maglev) technology has been applied in the traditional fields (rail transit and energy storage fields) and novel fields (astrophysics, space station microgravity, vibration isolation fields). As the key core components, HTS device should meet the requirements of volume, weight and cost, to improve the system operation efficiency. Thus, considering the low profile, miniaturization and lightweight characteristics of the double sided YBa 2 Cu 3 O 7-x (YBCO) thin film, we measured its levitation and relaxation characteristics. Meanwhile, we also designed the YBCO thin film with meander-lines, to explore the levitation characteristic evolution mechanism. It can be found from the experimental results that, the single piece of YBCO thin film with/without meander-lines can offer the levitation force more than 400 mN and 800 mN, respectively. The signature of this work is that the double sided YBCO thin film has the potential to be employed as the core device in the special application fields (such as astrophysics and space station), to supply the sufficient micro levitation force in limited volume and weight. [ABSTRACT FROM AUTHOR]

• Ag-doping is an effective way to enhance thermal conductivity and the superconductivity of YBCO superconductors. • The enhancement of thermal conductivity is limited. • Too much Ag 2 O doping will have a negative effect on superconductivity. • Ag-doping YBCO bulks are more suitable for applications which with a complex and varying external magnetic field like high-temperature superconducting maglev. Ag doping in (RE)Ba 2 Cu 3 O 7−δ [(RE)BCO] bulk high-temperature superconductors has been recognized as an effective way to improve the mechanical and superconducting properties of REBCO bulk superconductors for practical applications such as high-temperature superconducting (HTS) Maglev. Ag 2 O nanoparticles doped YBCO samples with different doping amounts (x , x varies from 0∼0.5 wt%) were fabricated by Top-Seeded Melt-Growth method (TSMG). The samples' steady-state thermal conductivity (λ) and the magnetic levitation force (F L) were measured by a testing platform under a similar condition to the HTS Maglev system. The effects of Ag 2 O doping on the λ and F L of single domain YBCO bulks have been systematically studied. The λ of the c -axis and the ab -plane were calculated through the steady-state heat flow method. We observed that λ increases distinctly when x ≥0.3 wt%. The doping amount of 0.3 wt% has been evidenced to be the optimal value, of which the λ of the c -axis and ab -plane are approximately 52% and 48% higher than the undoped one respectively. According to the results of the F L measurement, we found F L will increase while the relaxation rate of the F L will decrease by adding trace amounts of Ag 2 O nanoparticles in comparison to the undoped sample. This observation suggests that Ag-doping is an effective way to enhance thermal conductivity as well as the superconducting properties of YBCO superconductors for practical applications. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

• A magnetic-electric-mechanical coupling dynamic model for EDS is established. • The dynamic levitation force is verified by comparison with test results. • The pitching vibration mechanism of the bogie is analyzed. • A non-uniform exciting currents supply strategy is proposed and verified. The superconducting electrodynamic suspension (EDS) train is suitable for high-speed maglev rail transit because of its low drag force, strong levitation force, large suspension gap, and so on. However, the electromagnetic forces of four pairs of superconducting coils on one bogie are dynamically unequal in practical operation. This causes the bogie to vibrate in the pitching axis, which affects the train system's safety, stability, and comfort. Therefore, proposing an appropriate strategy to suppress the bogie pitching vibration is significant. First, based on the dynamic circuit theory, energy method and rigid body dynamics, the magnetic-electric-mechanical coupling dynamic model of eight superconducting high-field coils in the bogie and ground null-flux coils was established to explore the characteristics of fluctuating and unequal electromagnetic forces. The synchronous current and motion responses were further calculated using the Runge-Kutta algorithm. Second, the bogie's vibration characteristics were analyzed and the reasons for the vertical and pitching vibration were discussed. And the accuracy of the model was verified by comparing the levitation force with the experiment data. Third, a non-uniform exciting currents supply strategy for the superconducting coils was proposed under the comprehensive evaluation of the suppressing effect on the pitching vibrations. Finally, several cases were given to prove the effectiveness of the strategy. The results show that the total electromotive force increased by 0.005% after adopting the proposed non-uniform exciting currents supply strategy. But the minimum and maximum amplitude of pitching vibration and the growth rate of pitching vibration decreased by 97.00%, 95.76%, and 81.45%, respectively. This new strategy can effectively suppress the pitching vibration of the bogie without changing the already-designed mechanical structure. This established magnetic-electric-mechanical coupling dynamic model and the suppression strategy provide reference and a new idea for the superconducting EDS system's safety, stability, and comfort. [ABSTRACT FROM AUTHOR]

With the wide requirements of the training aids and display models of science, technology and even industrial products for the public like schools, museums and pleasure grounds, a simple-structure and long-term stable-levitation technology is needed for these exhibitions. Opportunely, high temperature superconducting (HTS) technology using bulk superconductors indeed has prominent advantages on magnetic levitation and suspension for its self-stable characteristic in an applied magnetic field without any external power or control. This paper explores the feasibility of designing a rotatable magnetic levitation (maglev) plate model with HTS bulks placed beneath a permanent magnet (PM) plate. The model is featured with HTS bulks together with their essential cryogenic equipment above and PMs below, therefore it eliminates the unclear visual effects by spray due to the low temperature coolant such as liquid nitrogen (LN 2 ) and additional levitation weight of the cryogenic equipment. Besides that, a matched LN 2 automation filling system is adopted to help achieving a long-term working state of the rotatable maglev plate. The key low-temperature working condition for HTS bulks is maintained by repeatedly opening a solenoid valve and automatically filling LN 2 under the monitoring of a temperature sensor inside the cryostat. With the support of the cryogenic devices, the HTS maglev system can meet all requirements of the levitating display model for exhibitions, and may enlighten the research work on HTS maglev applications. [ABSTRACT FROM AUTHOR]

To improve the curve negotiating ability of high-temperature superconducting (HTS) maglev system, a special structure of magnetic superelevation for double-pole Halbach permanent magnet guideway (PMG) was designed. The most significant feature of this design is the asymmetrical PMG that forms a slanting magnetic field without affecting the smoothness of the PMG surface. When HTS maglev vehicle runs through curves with magnetic superelevation, the vehicle will slant due to asymmetry in magnetic field and the flux-pinning effect of onboard HTS bulks. At the same time, one component of the levitation force provides a part of the centripetal force that reduces lateral acceleration of the vehicle and thus enhances its curve negotiating ability. Furthermore, the slant angle of magnetic superelevation can be adjusted by changing the materials and the thickness of the added permanent magnets. This magnetic superelevation method, together with orographic uplift, can be applied to different requirements of PMG designs. Besides, the applicability of this method would benefit future development of high-speed HTS maglev system. [ABSTRACT FROM AUTHOR]

In order to study the commonly neglected magnetic field information in the course of levitation force measurement process in a superconducting maglev system, a multipoint magnetic field measurement platform was employed to acquire magnetic signals of a bulk high- $$T_{c}$$ superconductor on both the top and the bottom surface. Working conditions including field cooling (FC) and zero field cooling were investigated for these vertical down and up motions above a permanent magnet guideway performed on a HTS maglev measurement system. We have discussed the magnetic flux variation process based on the Bean model. A magnetic hysteresis effect similar to the levitation force hysteresis loop of the bulk superconductor was displayed and analyzed in this paper. What is more valuable, there exists some available magnetic flux on the top surface of the bulk superconductor, and the proportion is as high as 62.42% in the FC condition, which provides an experimental hint to design the superconductor bulk and the applied field for practical use in a more efficient way. In particular, this work reveals real-time magnetic flux variation of the bulk superconductor in the levitation application, which is the other important information in contrast to the macroscopic levitation and guidance force investigations in previous studies, and it enriches the existing research methods. The results are significant for understanding the magnetic characteristic of superconductors, and they can contribute to optimize the present HTS maglev system design. [ABSTRACT FROM AUTHOR]

• A designed semi-active suspension system increases the damping of the HTS pinning maglev system with relatively little energy input. • The control logic and block diagram of the suspension system are presented. • The semi-active suspension is applied to an engineering vehicle through simulations. • This work provides references for the damping design of the HTS pining maglev vehicle. Based on the flux pinning characteristics of non-ideal type Ⅱ superconductors YBa 2 Cu 3 O 7-x , high temperature superconducting (HTS) pining magnetic levitation (maglev) is a self-stable levitation system with the merits of simple and reliable principle, friendly environment, etc. However, this maglev system is plagued by its prominent weak damping properties, which are unfavorable to the safety and comfort of the vehicle in operation under different external excitation. Therefore, the secondary suspension system should be added to this rail vehicle to enhance its damping property and its dynamic performance. This paper proposed a semi-active secondary suspension designed for the HTS pining maglev system. And this semi-active suspension can adjust the damping coefficient adaptively according to the motion state of the maglev vehicle. Moreover, an HTS pining maglev test vehicle "super maglev" is used to verify its effectiveness. Compared with the experimental and simulation results of a passive secondary suspension system, the dynamic performance of the maglev system with a semi-active suspension system is greatly improved. Furthermore, this semi-active suspension was applied to an engineering HTS pining maglev system through simulations. Eventually, through comparative analysis, the results show that the semi-active control damper controlled by PD can not only ensure the safety of passengers but also significantly improve the running stability of the vehicle, which has practical and economic advantages. [ABSTRACT FROM AUTHOR]

Off-centre operation of high-temperature superconducting (HTS) maglev systems caused by inevitable conditions such as the misregistration of vehicle, crosswind and curve negotiation, may change the distribution of the trapped flux in the HTS bulks and the magnetic interaction between HTS bulks and the PMG. It impacts on the performance of HTS maglev, and more seriously makes the maglev vehicle overturned. Therefore, understanding the performance of the HTS maglev in off-center operation is very important. In this paper, the dynamic response characteristics of a cryostat with twenty-four onboard YBaCuO superconductor bulks were experimentally investigated at different eccentric distances under loads before the initial FC process. Parameters such as vibration accelerations, displacement, natural frequency and dynamic stiffness were acquired and analyzed via the B&K vibration analyzer and laser displacement sensors. Results suggest that the natural frequency and dynamic stiffness of the maglev vehicle would be obviously reduced with the eccentric distance, posing negative effects on the stability of HTS maglev. [ABSTRACT FROM AUTHOR]

The evacuated tube provides a vacuum condition so that the high temperature superconducting (HTS) Maglev could run at an ultrahigh-speed. While inside the tube, the low-pressure environment could reduce air friction effectively, which is considered to be the main resistance to the Maglev. However, low-pressure would affect the evaporation state of liquid nitrogen (LN2), which is used as the coolant to ensure that the superconductor bulk could reach its superconducting state. This paper studied the evaporation characteristics of LN2 under different pressures, which influence the working time of the HTS Maglev vehicle directly. The results provide an important reference for the evacuated tube HTS Maglev. [ABSTRACT FROM AUTHOR]

It is important to understand the influence of environmental temperature variation on high temperature superconducting (HTS) maglev performance in practice. As the on-board bulk high temperature superconductors (HTSCs) are kept in liquid nitrogen cryostats at all times, the actual temperature effects relevant to maglev performance are on the permanent magnet guideway (PMG), and these have been examined by exploring the PMG magnetic characteristics and the related interaction force with the on-board bulk HTSCs above it in this paper. The experimental temperature range was set from room temperature to 77 K. The experimental results show that the typical room temperature (RT) vertical magnetic flux density (defined as B PMG ), 565 mT, of the PMG segment first increases as the temperature decreases to 138 K, before it reaches a peak of 634 mT within the temperature range from 138 K to 120 K, with a rapid growth rate to 12.2% over the RT value. And then B PMG decreases quickly to a stable value of 576 mT at 77 K. A final 1.9% enhancement ratio was obtained compared with the initial B PMG at room temperature. Furthermore, the levitation force exhibits a similar trend to the B PMG whatever the field cooling process and the zero field cooling process was conducted when the PMG temperature is reduced. Growth of 21.8% and 13.4% for the levitation force occurs for the field-cooling process and the zero-field-cooling process, respectively. The results provide basic data for environmental temperature effects on HTS maglev systems, which implies that the low temperature environment can have benefits towards enhancement of their levitation performance. [ABSTRACT FROM AUTHOR]

High temperature superconducting (HTS) maglev technology is becoming more and more mature, and many key technologies have been deeply studied. However, the transition curve plays a key role in HTS maglev system, and related studies have not been carried out. In this paper series of simulations were conducted to test the lateral and vertical vibration of HTS maglev when passing through curves. Two magnetic guideways, of which one has transition curves but the other does not, are designed to test the vibration characteristics of a mini HTS maglev model running though curves. Results show that after adding transition curves between straight line and circular curve the vibration of HTS maglev model in lateral and vertical directions are all weakened in different degrees. It proves that adding transition curve into HTS maglev system is favorable and necessary. [ABSTRACT FROM AUTHOR]

• A 9.5-hour running experiment was conducted in the self-developed measurement. The results of three simulation methods show that indirect coupling by numerically PMG has a good performance in time consumption and accuracy. And the accuracy of the simulation model is verified by 9.5 hours of experiment. • Considering the self-oscillation frequency of HTS maglev, a comparison of the different working conditions from 0.5 Hz to 10 Hz shows that there is no direct relationship between the levitation force and frequency in the self oscillation frequency range. • The continuous 30 days operation was calculated to simulate long-time levitation performance of HTS maglev vehicle. When the vibration amplitude is constant, the levitation force has a logarithm relationship with time. When 10 mm is applied as the working height, after 30 days, considering the maximum 2 mm amplitude (4 m/s2 vertical vibration acceleration), the average LF decreases by 28.8 % and the levitation height decreases by 1.74 mm. • Taking the 12 hours of long-term service HTS maglev trains into consideration, a margin of 25% LF is suggested, or a 1.5 mm levitation height margin should be reserved in the design of the whole system levitation capacity. Taking the common 10 mm LH design as an example, the 12 mm LH can be chosen as the initial LF to ensure LH is above 10 mm after running for 12 hours. • To investigate the influencing factors and improve the levitation force decay, the preload method was carried out to keep the levitation stability for a long time. It is suggested to the recommended preload height be selected as the amplitude value increased by 1 mm. The optimal working condition is for the vibration amplitude to be limited to 1 mm, and to use a preload height of 2 mm. In order to explore the long-time evolution of the high-temperature superconducting (HTS) maglev levitation force (LF), this paper uses the self-developed HTS dynamic maglev measurement device to conduct a long-time dynamic experiment. Limited by the experimental conditions, further working conditions are conducted based on the dynamic simulation model which is constructed based on COMSOL Multiphysics by using the magnetic field intensity H method and the basic electromagnetic formula of superconductors. The accuracy of the simulation model is verified by 9.5 h of experiment. Based on the simulation model, the LF change and levitation height decay of HTS maglev under the vehicle vibration excitation for a long time are explored. Firstly, considering the self-oscillation frequency of HTS maglev, a comparison of the different working conditions from 0.5 Hz to 10 Hz shows that there is no direct relationship between the LF and frequency in the self-oscillation frequency range. Secondly, a 30 days operation under 0.1 Hz external excitation is calculated to simulate long-time evolution and regularity of HTS maglev, which shows the LF decay has a logarithmic decay regularity with time. Furthermore, to investigate the influencing factors and improve the LF decay, the preload method was carried out. The work can provide a predictive model and data reference for the long-time performance of the HTS maglev engineering vehicle. [ABSTRACT FROM AUTHOR]

In order to enhance the guidance force, adding the high-temperature superconducting (HTS) bulks and permanent magnets in lateral direction is the simplest way especially in curve negotiation situations. However, as the core component of maglev system, permanent magnet guideway (PMG) consists of a huge amount of NdFeB magnets along the operation line. Hence, it means a huge construction cost to add the magnets in lateral direction. To help solving this issue, this paper discusses a PMG improvement methodology based on the widely-used two-pole Halbach PMG. This proposed novel PMG can enhance the guidance force by only adding air intervals between neighbor magnets and the flux-concentration irons and raising the onboard HTS bulks' width accordingly. Firstly, a 2D electromagnetic theoretical model of the HTS bulk-PMG maglev system was built in the COMSOL Multiphysics. Then, under the different external magnetic fields of the PMGs with different air intervals, levitation and guidance performances of the typical onboard HTS bulk array at typical working conditions were discussed. The results showed that, with the suitable HTS bulks' width, the guidance force can increase with the intervals increasing in a range. And the HTS maglev system adopting this idea can achieve a guidance force growth of about 41%. This PMG idea is appropriate for curve negotiation situations because of its higher ratio of the guidance force to the levitation force, without changing the basic magnetic circuit and the magnet block number of the previous linear PMG. • An efficient permanent magnet guideway (PMG) improvement idea for curve negotiation was proposed. • The PMGs with different parameters were compared in force performances, and one PMG structure was recommended. • Both the guidance force and the ratio of the guidance force to the levitation force were raised significantly by the new PMG. [ABSTRACT FROM AUTHOR]

• A more precise HTS vehicle / track coupling model is established by adding a flexible permanent magnet track (PMT) to the HTS vehicle / track coupling system. • The theoretically infinitely long, discrete-supported PMT is abstracted as a finite-length, simply-supported Euler beam at both ends, and the correctness of the model is verified by the finite element method. • The force between the dewar and the PMT is considered as a uniformly distributed load, which is consistent with the actual situation. • The effects of different system parameters (e.g. track support spacing, stiffness values of elastic supports, etc.) on the vehicle dynamics were investigated. • Considering the stability of vehicle operation and the response of flexible track, a reasonable design of PMT system is given. High-Temperature Superconducting (HTS) Maglev has the potential to run at high speed with the advantages of stability. As a kind of track transportation vehicle, the performance of vehicle-track coupled vibration will affect the comfort and safety of vehicle operation. In this paper, the track structure is analysed and designed based on the dynamic response of vehicle-track coupling. The model of long pillow embedded ballastless track is used to simulate the discrete permanent magnet track supported by the fastener and elastic rubber pad under the fastener. Through the calculation of the coupling system of HTS maglev train, the vehicle dynamic performance under different fastener stiffness, different fastener distance and different speed is obtained. The dynamic performance of the vehicle is quantitatively evaluated by the maximum acceleration of the car body, fluctuation of suspension gap and the running stability of the vehicle. The vibration responses of vehicles and tracks under different working conditions are discussed, and reasonable design suggestions are given. [ABSTRACT FROM AUTHOR]

Abstract: In practical application of High-T c Superconducting (HTS) maglev, slant is an observable defect. It was caused by constantly one side on and off the vehicle by passengers. So far, this phenomenon has not been reported yet. In order to understand its influence on the stability of the HTS maglev, we experimentally studied the dynamic characteristic and slant effect of HTS maglev under center-load and side-load. It was found that load destabilizes the vehicle, and the side-load can obviously slant the vehicle body. In the end, the pre-load method was proposed to enhance the dynamic stability and suppress the slant, which proved to be considerably effective. These results are critical in practical running of HTS maglev. [Copyright &y& Elsevier]

• An optimized Halbach structure designed for repulsive force was proposed. • The dimension relationship among magnet rail, permanent magnets on the vehicle, and lateral movement has been put forward. • With the new Halbach structure, both the stability and load-capacity of the permanent magnetic levitation were improved. The hybrid maglev system taking advantage of better carrying capacity in permanent magnetic levitation (PML) and self-stability in superconducting magnetic levitation (SML) has been put forward. PML and SML can share the same magnet rail, which is arranged in Halbach arrays to concentrate the magnetic field on the working region and save magnet materials. Recently, the manned hybrid maglev prototype has been built in Chengdu, China. In this paper, we focus on the PML part, in which the characteristics of the levitation force and the lateral force were studied since they are key factors for load capacity and stability. The research was carried out with both analytic expressions and finite element method. With the relationship between magnetic force and lateral displacement, the recommended maximum lateral displacement was proposed. In addition, considering the end effect of Halbach array, an optimization PML model was designed, which can not only improve the levitation force but also reduce the lateral force. The study offers a reference for the further design and optimization on the PML or the hybrid maglev system involving it. [ABSTRACT FROM AUTHOR]

Since the potential widespread applications of RE–Ba–Cu–O superconducting bulks, it is crucial to enhance their superconducting performances. Binary oxide HfO 2 nanoparticles were added into Gd–Ba–Cu–O superconducting matrix before the melt textured growth process. It was found that the HfO 2 particles reacted with surrounding matrix and consequently formed BaHfO 3 inclusions maintaining nanoscale without significant ripening during the melt growth process. The superconducting transition temperature T C is almost not affected by HfO 2 addition, and interestingly, the T C of 0.8 mol% HfO 2 doped sample increases slightly by about 0.1 K in comparison with the undoped one. Meanwhile, the critical current density J C was improved over the whole magnetic field range. These BaHfO 3 particles discovered near the liquid phase (Ba–Cu–O, Cu–O, etc.) should be the origin for the improvement of flux trapping capability and critical current density in this system. [ABSTRACT FROM AUTHOR]

• The auto-filling LN 2 system ensures the cryogenic environment for YBaCuO superconductors. • The results proved that the auto-filling LN 2 system has the high detection precision and filling efficiency. • The prototype has been implemented and tested successfully on the "Super-Maglev" HTS maglev vehicle. • The system is very encouraging for the practical application of HTS maglev systems. The cryostat equipped with superconducting materials is one of the most important component of high-temperature superconducting maglev vehicles. However, due to the multiple energy disturbance forms in the cryostat, such as AC losses of superconductors, vibration of the cryostat and so on, the evaporation of liquid nitrogen (LN 2) will be stimulated to accelerate, which will seriously threaten the vehicle safety. Therefore, this paper designs an intelligent controller which can realize the function of auto-filling LN 2 based on the Kalman filter (KF) algorithm. Moreover, in this publication the corresponding methodology will be described as well in detail. Initially, the platinum resistance sensors were used to study the relationship between the temperature and LN 2 level, meanwhile, the system state equation and observation equation were established. Then, the KF algorithm was introduced to estimate the true LN 2 level. Based on the feedback signal of LN 2 level, the system utilizes the STM32 microprocessor as control chip to control the solenoid valves and realizes the function of auto-filling. The controller has been implemented and the total time for filling one cryostat was reduced from 86 min to 16 min. This result is very encouraging and inspiring for the practical application of HTS maglev systems. [ABSTRACT FROM AUTHOR]