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High-temperature superconducting (HTS) maglev has been developed rapidly in the last few decades. Due to its numerous advantages, such as self-stabilization, low energy consumption, no mechanical friction, and being environmentally friendly, researchers from all around the world have done a large amount of research to promote the engineering application of HTS maglev. The researchers have found that during the operation of HTS maglev, the primary source of external disturbance is the permanent magnetic guideway (PMG) irregularity. It is composed of geometric irregularity and magnetic field inhomogeneity. When evaluating the irregularity of the PMG used in the HTS maglev system, it is different from the traditional railway track. The difference is reflected in that not only the geometric irregularity but also the inhomogeneous distribution of magnetic field at the working height of superconductors should be considered. So far, the research on PMG irregularity is not complete. There is no track spectrum for PMG irregularity by now. The track structure and vehicle-track coupling mode of HTS maglev system are fundamentally different from that of other rail transit systems. When investigating the vehicle-track coupling dynamics of HTS maglev system, it is not accurate to substitute the track irregularity spectrum of other rail transit systems for PMG. Therefore, it is necessary to measure and characterize the irregularity of PMG. First, to measure the geometric irregularity and magnetic flux density at the position of 10 mm above PMG at the same time, an irregularity detection equipment is designed. Then, the PMG of the ring test line in Southwest Jiaotong University is measured by the equipment. According to the measured geometric irregularity, using the form of the power spectral density function of track irregularity proposed by the Chinese Academy of Railway Sciences, the PMG geometric irregularity spectrum is obtained. Next, the measured magnetic field inhomogeneity caused by the structure of PMG and the edge effect of magnets is analyzed. Subsequently, a method is proposed to convert the magnetic field inhomogeneity into equivalent geometric irregularity. Superimposing it with the actual geometric irregularity, the sample of PMG irregularity considering both geometric irregularity and magnetic field inhomogeneity can be generated. This article provides a measurement scheme and characterization method of PMG irregularity. It can also make a reference for the vehicle-track coupling dynamics analysis of HTS maglev. [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]

With regard to the state-of-the-art technologies in the fields of applied superconductivity and electromagnetic devices, research and development highlights are presented. The recent progress and achievement described with principle and technical details include mainly i) applied superconducting materials; ii) superconducting magnets and their applications such as in ITER and Tokamaks; iii) high Tc superconducting (HTS) magnetic levitation and applications; iv) HTS smart grids; v) superconducting and electromagnetic material modelling and characterization; and vi) advanced electromagnetic devices. The applied superconductivity technology and availability are especially focused and verified with the trend of development prospection. [ABSTRACT FROM AUTHOR]

With the merits of self-levitation, self-stabilization, zero magnetic drag, environment-friendliness, and low energy consumption, high-temperature superconducting (HTS) maglev is regarded as one of the main technology modes for the future rail transit. For the researches on the lateral-vertical coupled dynamics of the HTS maglev, there is still a lack of lateral-vertical coupled force model that can characterize the macroscopic force between high-temperature superconductor and permanent magnet guideway (PMG). In this article, a scanning experiment of levitation force and guidance force in a selected area on the vertical plane was carried out, and the law of levitation force and guidance force changing with coordinates was studied as well. Moreover, the finite element method was used to calculate the magnetic field distribution of the Halbach-type PMG, meanwhile, the Lorentz force formula was utilized to analyze the influence law of PMG's magnetic field on the levitation force and guidance force. On the basis of this research, a 2-D force model that neglects the hysteretic between high-temperature superconductor and PMG was established. By comparing the simulation results of the model with the measured data of the experiment, it is found that both of them are in good agreement, which verifies the reliability of the proposed model. The 2-D force model is very helpful to the future research and calculation of the dynamics of the HTS maglev. [ABSTRACT FROM AUTHOR]

Dynamic electromagnetic characteristics is significant for the design and operation of superconducting (SC) electrodynamic suspension (EDS) train. This paper established a three-dimensional transient numerical model in COMSOL. The current density excitation comes from the homogenized model of the superconducting magnet. In order to decrease the computing time, periodic boundary is introduced taking the place of finitely long route. Mapping operator is adopted to ensure the continuity of physical quantities in the case of geometric discontinuity in the process of motion. Induced current and magnetic force at different operation velocity and different structure are simulated. In general, this model could be applied to simulate long term operation. It is also suited for the simulation of propulsion systems for EDS systems. In addition, this model provides electromagnetic environment intuitively that would be helpful for the stability analysis and design of onboard SC magnets during long term operation. [ABSTRACT FROM AUTHOR]

High-temperature superconducting (HTS) maglev system, based on the magnetic flux pinning characteristic of non-ideal type II superconductors, can realize self-stable above permanent magnets. HTS maglev possesses the advantages of low-energy consumption, simple mechanical structure and environment-friendly, which make it an ideal high-speed transportation mode. When an HTS maglev vehicle crosses a ramp, the levitation height will fluctuate due to the rapid change of the track curve, which may affect the safety and stability of the system. In this paper, first, a levitation force model was obtained based on experimental data. Based on this model, a dynamic model of the HTS maglev vehicle-bridge coupled system was established. The dynamic response of the maglev train was simulated and analyzed when it operated through track grade change points under different track slopes, vertical curve radii and speeds. The influence of these parameters on the stability of the system was investigated, and the optimized design parameters for the vehicle and the track slope are proposed as well. This study provides references for the future engineering development of HTS maglev transportation. [ABSTRACT FROM AUTHOR]

In the practical application of high-temperature superconducting (HTS) magnetic levitation, the influence of ambient temperature on its performance is mainly reflected in the change of magnetic characteristics of the permanent magnet guideway (PMG). In order to investigate the magnetic characteristics of the PMG at high temperature and the influence of temperature on the levitation performance of HTS bulk above, we studied the magnetic characteristics of three kinds of PMG and six kinds of single permanent magnet (PM) in the temperature range from room temperature to 85 °C. Furthermore, we investigated the effect of this variation on the levitation performance of HTS bulk under a zero-field-cooling condition. The results show that the N-S-S-N-type PMG-H has better magnetic field stability than the Halbach PMG-I and the N-N-S-S-type PMG-J at high temperature. The levitation force of HTS bulks decreases with the increase of the PMG temperature. The variation range of levitation force is larger than that of magnetic field of PM, but absolute values under 55 °C are small. This work provides a reference for the engineering PMG optimization of HTS magnetic levitation. [ABSTRACT FROM AUTHOR]

Due to the strong magnetic force between segments of the permanent magnet guideway (PMG), the unmovable electromagnetic turnout becomes one of the most possible choices for high-temperature superconducting (HTS) maglev systems. Meanwhile, it has advantages of quicker response and smaller volume compared with mechanical turnout. A complete turnout system is vital for further evaluating feasibility. Based on the previous studies in ASCLab of Southwest Jiaotong University, a complete electromagnetic turnout prototype system is introduced in this article, which consists of two electromagnets, a Halbach type PMG, a control system, and a maglev vehicle model with a single-domain YBaCuO cylindrical bulk superconductor. In order to guarantee the stable running of vehicle at the turnout area, electromagnets are necessary to provide a similar magnetic field compared with the normal Halbach PMG. Based on the system, the measurement on the magnetic field was done and indicates that the electromagnet could replace permanent magnets of guideway to create a similar magnetic field distribution. The magnetic field experiment on this prototype system further certifies the applicability of the Halbach electromagnetic turnout. For future HTS maglev transportation, the electromagnetic turnout could be widely used in low-speed application such as railway station, switchyard, and laboratory. [ABSTRACT FROM AUTHOR]

To enhance maglev competitiveness in passive stability and simple structure, a manned hybrid maglev vehicle applying permanent magnetic levitation (PML) and superconducting magnetic levitation (SML) was developed. The vehicle is mainly composed of a maglev frame, a PML part, and an SML part. The maglev frame was employed to connect the PML and SML parts. Based on the magnetic rail of our high temperature superconducting maglev test line of the “Super-Maglev,” the onboard levitation components are bespoke to match the magnetic rails. The PML part is assembled to the maglev frame by vertical linear sliders, and is able to move freely in the vertical direction for appropriate heavy load. The driving method is linear induction motor whose primaries are installed between two rails, interacting with the induction plate mounted on the SML part. The rated load is designed as 375 kg and achieved for one passenger at 15 mm field cooling height. Measurements of its mechanical property were performed under static loads. Results display that the manned hybrid maglev vehicle possesses good advantages of load ability and passive stability at the same time. The work explores a new feasible combination of the PML and the SML for maglev applications. [ABSTRACT FROM AUTHOR]

High-temperature superconducting (HTS) bulk YBa2Cu3O7‐x (YBCO) can achieve self-stable magnetic levitation (maglev) over a permanent magnet (PM) for its inherent flux pinning effect, which has considerable potential for engineering applications. The complicated vibration response, however, is lacking in research for the nonlinearity of the interaction force between the HTS bulks and PMs. This paper mainly focuses on the subharmonic resonance of the HTS bulks YBCO levitating above the PMs in Halbach array, which are in reciprocating motion, by numerical simulations. In general, the motion of HTS bulks is approximately harmonic under limited excitation. When the amplitude and frequency of the excitation satisfy certain conditions, the dynamical system undergoes a period-double bifurcation, and then, the subharmonic resonance occurs. Moreover, the period-double bifurcation brings the jump phenomenon when the frequency of excitation increases and decreases at the double of eigenfrequency nearby. Simulations show that a suitable damping is able to reduce the vibration markedly. The subharmonic resonance region in an amplitude-frequency plane is presented in this paper finally. In a word, the subharmonic resonance would occur in an HTS maglev system under certain conditions and its prediction is numerically studied here with a nonlinear mathematics model of the levitation force. [ABSTRACT FROM AUTHOR]

In practical high-temperature superconducting (HTS) maglev systems, it was found that the levitation force of the onboard bulk superconductors may attenuate gradually under the inhomogeneous magnetic field. The corresponding phenomenon is that the levitation height will decay in the macroscopic and affects the long-term stability of the maglev vehicle. Thus, it is of great significance to study the dynamic levitation force of bulk superconductors under a varying external magnetic field and lay a foundation for the moderate and high-speed HTS maglev system application. In this paper, first, an experiment related to the dynamic levitation performance of YBCO bulks is carried out with a self-developed HTS maglev dynamic measurement system for the investigation of force attenuation. Then, a corresponding two-dimensional simulation model based on the finite element software of COMSOL Multiphysics 5.3 is built to research the dynamic levitation force of bulk superconductors moving above a nonuniform magnetic field. In the simulation, the electromagnetic properties are calculated using the H-formulation, and the moving mesh is employed to implement the relative movement between the bulk superconductors and permanent magnets. The experiment process is repeated in the simulation model, and the simulation results agree with the experimental results. [ABSTRACT FROM AUTHOR]

Taking the influence of low pressure on levitation performance of high temperature superconducting (HTS) maglev into account, we established a simple super-cooling platform based on pumping method to study the levitation performance of YBCO bulks above the Halbach permanent magnet guideway (PMG) under different pressure conditions. Through measuring the temperature of liquid nitrogen (LN2) during the decreasing process of pressure, it is known that the LN 2 would turn into a super-cooling state as the pressure reduction. Measurements of the levitation force versus vertical motion and the force relaxation were performed both in case of zero-field-cooling (ZFC) and field-cooling (FC). The experimental result showing that the decreasing pressure is beneficial to improve the levitation performance of HTS bulks, and the maximum force increase up to 23.5% and 22.1% were realized in ZFC and FC compared with the atmospheric pressure, respectively. Moreover, the low pressure could also reduce the hysteresis loop area and restrain the relaxation decay of levitation force. These results imply that, the low pressure environment in evacuated tube will be beneficial to the levitation performance of HTS maglev system [ABSTRACT FROM PUBLISHER]

The track regularity of a permanent-magnet guideway (PMG) is an important issue to ensure the riding comfort and running stability of high-temperature superconducting (HTS) maglev vehicles. Compared with defects of typical railway tracks, similar defects on PMG could affect the magnetic field at the levitation height and then influence the running performance and the riding comfort of the maglev system. In this paper, the influence of four kinds of Halbach PMG defects on magnetic field distribution was investigated by a finite-element simulation method. According to the calculation results, it is found that the sensitivity of the magnetic field inhomogeneity varies with each kind of defect. The vibration experiments found that the magnetic field inhomogeneity does bring vibration to HTS maglev vehicles. The results could provide significant references for future PMG design in the HTS maglev system. [ABSTRACT FROM AUTHOR]

Bulk high-temperature superconductors with a rectangular shape are easy to realize a compact assembly, which is promising for maglev applications. In order to find a reasonable array pattern, we have studied the levitation force of four multiseeded rectangular YBaCuO blocks with three possible arrays above two different permanent-magnet guideways (PMGs). Experimental results show that the levitation force can be improved by optimizing the array pattern of the bulk superconductors. An effective method to improve the utilization rate of the applied magnetic field is to avoid the joint air gaps between bulks located in a strong magnetic field area of the PMG. The optimal array pattern is able to enhance the levitation performance of the present superconducting maglev vehicle. [ABSTRACT FROM PUBLISHER]

The mechanical bearing in the cryogenic liquid pump has short working life due to the low temperature environment. For conquering the disadvantage, the radial high temperature superconducting magnetic bearing (HTSB) is designed to be used in the cryogenic pump. The high temperature superconductors (HTSs) in the HTSB are cooled by the cryogenic liquid directly. The introduced cryogenic liquid pump can constrain the heat leakage. The equipment for the kinetic characteristics of the HTSB is introduced, and it can measure the axial forces of the HTS at different rotation speeds. Basic mechanical principle of the rotor of the pump is analyzed. [ABSTRACT FROM PUBLISHER]

The strongly connected or coupled grain boundaries (GBs) between adjacent grains and their macroembodiment as flowing intergrain supercurrents crossing the GBs inside multiseeded bulk high-temperature superconductors were elucidated by trapped-flux evaluation. Trapped-field measurements, after cutting and polishing two multiseeded YBCO bulk samples, were conducted to present the existence of coupled GBs and their distribution along the c-axis growth. The intensive trapped-flux density observed near the GB areas inside the whole sample is direct evidence of a strongly connected or coupled GB. The relatively strong trapped flux near the GB areas and the significant improvement of the total trapped flux compared with the isolated single-grain bulks were ascribed to the intergrain supercurrent flowing across the GBs in large macroscopic loops with coordination of the intragrain supercurrent circulating in each grain of the multiseeded bulk. Based on the experimental results, a simplified simulation model that incorporates two forms of the intra- and intersupercurrents flowing inside the multiseeded bulk is introduced to reproduce the trapped-flux density features, and qualitative agreement is obtained by comparison with the experimental ones. [ABSTRACT FROM AUTHOR]

After clarifying the essential characteristics of the multiseeded YBCO bulk in the previous work, that is, the existence of strongly connected or coupled grain boundaries between two grains by means of intergrain super current with a big flowing loop size, this paper proceeds to report its achievable performance in actual excitation conditions by working as trapped-field magnets or levitation devices. Besides evaluation of the trapped-flux characteristics by two most popular excitation methods, namely, static field-cooling magnetization (FCM) and pulsed-field magnetization in liquid nitrogen (LN2), the trapped-flux capability at lower temperatures up to 30 K, an interesting temperature for present superconducting machine applications, is also reported. From LN2 temperature to 30 K, the trapped flux with over six times improvement from 0.64 to 3.91 T was observed by FCM, at the same time along with a much decreased relaxation rate from 13.7% to 0.9% in 1-h measurements. In the aspect of levitation applications, the magnetic force density (both levitation force and guidance force, two most important performance parameters for maglev) above a permanent magnet guideway with Halbach style is measured and found to be able to promote the loading and stability performance of the first high-temperature superconducting maglev test vehicle simultaneously. As the multiseeding technique of the top-seeded melt-growth process has provided a promising way to fabricate bulk superconductors with large size, time saving and cost reduction, the presented trapped-flux and magnetic force results may help to comprehend, refer, and finally make better use of the multiseeded bulks in the large-scale superconducting magnetic devices. [ABSTRACT FROM AUTHOR]

Aiming at exploiting the high trapped field ability of bulk high-temperature RE-Ba-Cu-O (RE: rare-earth elements) superconductors, a brushless axial-gap type superconducting synchronous motor has been successfully developed as a technology demonstrator using eight melt-textured GdBa2Cu3Oy (Gd-123) bulks as pole-field magnets. An output power of 10 kW at 720 rpm was realized by an average trapped field peak of 0.56 T reaching the armature coils, under a pulsed field excitation at the liquid nitrogen temperature. For such motors, to improve the trapped flux of bulks is a direct way to enhance the motor performance. In order to obtain a high trapped flux density with a regular shape for a high performance motor utilization, the pulsed field magnetization (PFM) properties of two kinds of bulk superconductors have been investigated. By a reasonable multi-PFM process with a pair of vortex-type pulsed coils, it was found that the multi-seed Y-Ba-Cu-O bulk can bring a high average trapped field, while the single-grain Gd-Ba-Cu-O bulk under a size-adjustable pulsed coil can obtain a very regular trapped field distribution. These results will be useful to the following optimization of the rotating machine system. [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]

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]