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The introduction of high temperature superconducting (HTS) magnet, which is capable of working at liquid nitrogen temperature, and the use of null-flux coil, make the liquid-helium-free electrodynamic suspension (EDS) train available. In essence, the electromagnetic force of a superconducting EDS train is generated by electromagnetic interaction between the onboard superconducting magnets and the ground null-flux coils. In order to obtain an efficient HTS EDS train, the design optimization of the HTS magnets and null-flux coils is indispensable. This study is devoted to this aspect. We first establish an improved load-line method for efficiently estimating the critical current of HTS magnets and an improved semianalytical model to accurately calculate the induced currents and electromagnetic forces in the EDS train. Based on above two improvements, the onboard HTS magnets and corresponding null-flux coils are then designed and optimized to enhance the overall performances of the HTS EDS train. At final, according to the optimized results, the HTS magnets and null-flux coils were manufactured and measured, followed by the performance analyses of the obtained HTS EDS train. The results have shown that the electromagnetic performances of the designed HTS EDS train are excellent, demonstrating the effectiveness of the optimization methodology.

Stacking structure is the widely-accepted method to improve the current carrying capacity of second-generation high temperature superconducting (2G HTS) tapes. Meanwhile, due to the influence of high aspect ratio, narrowing concept becomes an effective way to improve the electromagnetic characteristics of HTS tapes. Solder-Stacked-Square (3S) HTS wire is novel HTS conductor with 1 mm width, which is derived from the normal HTS tapes and combined the meaning of both stacking and narrowing. As is known, the external magnetic field affects the critical current of HTS tapes. In order to get the reliable critical current of 3S HTS wire for the real application, it is important to evaluate the magnetic field dependence of 3S HTS wire in detail. However, the stacking process makes the 3S wire structure flexible and changeable. To be clear about the stacking effect of 3S wire on the critical current, we prepared 3S wire samples, which are respectively stacked by three different structures. In this paper, we measured the magnetic field dependence of critical current for these 3S wire samples. The experimental results are the necessary support for the design of 3S wire applications.

A new HTS maglev vehicle called “KENYON” that can carry 8 passengers was successfully developed in December 2019. The vehicle adopted the bogie structure of independent running gear, which brings the improvement of curve passing performance. In order to further optimize vehicle curve passing performance in view of the small radius curve of the ring test line, corresponding experimental research was carried out in this paper. The experimental results show that the small wheelbase and centripetal arrangement were beneficial to improve the vehicle's curve passing ability.

China Fusion Engineering Experimental Reactor (CFETR) is a major scientific project independently designed and developed by China and jointly with international cooperation. Engineering design and project infrastructure construction are currently underway. The design goal of CFETR is 1.5–2.0 GW fusion power, and the central magnetic field is up to 15 Tesla, which is much larger than the design parameters of ITER under construction in Europe. In order to achieve the desired high magnetic field, the pre-research of Bi-2212 high temperature superconducting CICC magnet was carried out. The performance test of Bi-2212 cable is the most direct criterion for the successful development of the cable. New cable performance judgment method is proposed because of the long test time and high test cost of sub-size cables. Two cables are manufactured, and one cable is disassembled into single wires for performance evaluation. If the performance of single wires is not significantly attenuated in comparison with the performance of single wires that have not been twisted, we will conduct the second cable critical current test. The test results show that the method of dismantling the cable test is feasible. It is also feasible for cables of different structures. This method can be used to judge the performance of the cable in advance. This method is only suitable for detecting damage in the cable manufacturing process.

The Tri-axial high temperature superconducting (HTS) cable usually subjects to the impact of the fault currents in the power system. During the fault, a large amount of the Joule heat is generated, which may be damage cable. In this paper, an analysis model of electromagnetic thermal transient characteristics of the 10 kV/1 kA cable is built. The transient characteristics of the HTS cable are analyzed under a fault current of 15 kA rms lasting 0.14 s, and the current, resistance and temperature of the HTS cable are obtained. The maximum temperature of the HTS cable is 153.1 K under fault current. Meanwhile, the safe operating range of the HTS cable under the fault current of 15 kA to 25 kA is obtained. the analysis results will provide the theoretical basis for the quench protection and relay protection strategy of the tri-axial HTS cable in the Grid.

Combining several high temperature superconducting (HTS) tapes into an assembled HTS conductor can enhance the current-carrying capacity, mechanical strength and improve the large width-to-thickness ratio of HTS tapes. And in practical applications, joints can extend the assembled HTS conductors to required lengths. Therefore, encapsulated joints for Soldered-stacked (SS) wire has been proposed as a preliminary study to achieve long length Soldered-Stacked-Square (3S) wire. And in this paper, we numerically study the performances of different types of encapsulated joints. Firstly, encapsulated joints are divided into two categories according to their positions, and a nonlinear circuit model is presented to demonstrate the numerical study process and experiments are conducted to determine the parameters in this model. Then, resistance performances of the encapsulated joints are discussed such as the “multilinear resistance” phenomenon where the encapsulated joints show different resistance under different current. And HTS tape arrangements in the encapsulated joint are also discussed to achieve minimum resistances.

The tube structure is an important guarantee for the dynamic stability of the high temperature superconducting maglev-evacuated tube transport (HTS Maglev-ETT) system, it is necessary to conduct relevant research on it. Based on simulation calculations with the FLUENT software, this paper studied the influences of different tube section forms on the aerodynamic drag of maglev train in tube, as well as the pressure distribution in the tube system. In addition, the effects of the setting of cross aisle on the aerodynamic drag of maglev train and pressure fluctuation of flow field in tube were also studied. It was found that the difference in the section forms of tube has little effect on the aerodynamic drag of maglev train and pressure distribution of the tube system under low pressure; the setting of cross aisle can be helpful to reduce the aerodynamic drag of maglev train and the pressure fluctuation around the train to a certain extent. Therefore, the design of cross aisle is recommended for the HTS Maglev-ETT system.

In the field of high-temperature superconductors, atom probe tomography is a relatively new instrument, with the ability to provide a new perspective on the 3D nanoscale microstructure. However, field evaporation of nonmetallic materials is fraught with unique challenges that matter little in the world of metallic evaporation. In this study, we review the laser absorption, correlated evaporation, molecular dissociation, and the crystallographic effects on the field evaporation of 800-m ${\rm RB}{\rm a}_ 2{\rm C}{\rm u}_ 3{\rm O}_{ 7-{\rm \delta }}$ (R = Gd, Sm) coated conductor tapes deposited by Reactive Co-Evaporation Cyclic Deposition and Reaction (RCE-CDR). Ultraviolet 355 nm laser pulsing was found to have a substantial beneficial effect on minimizing the fracture probability compared with 532 nm illumination, especially when evaporating insulating oxide precipitates. This, in turn, allows for the 3D compositional analysis of defects such as flux pinning centers introduced by precipitation and doping. As a result, evidence for the precipitation of nanoscale ${\rm G}{\rm d}_ 2{\rm C}{\rm u}_ 2{\rm O}_ 5$ is discussed. The effect of crystallographic orientation is studied, where [001] aligned evaporation is found to develop compositional aberrations.

Superconducting devices composed of the second-generation high-temperature superconducting (2 G HTS) RE-Ba-Cu-O (REBCO, RE is rare earth) tapes have extensive applications in high magnetic flux den...

Experiments on quench propagation in high-current, high field High Temperature Superconducting (HTS) Cable-In-Conduit Conductors (CICCs) for fusion applications are forthcoming. Among the conductor designs to be tested, there is the ENEA slotted core proposal. In order to support the design of the samples and plan the diagnostics to be employed, a 1D multi-region thermal-hydraulic and electric model of the samples has been developed using the H4C code. After an experimental electric characterization, the model is applied to the simulation of quench propagation in the samples. The simulations show how current redistributes among the tapes and the slots. Additionally, they show that the quench protection strategy is suitable to prevent too high hot-spot temperatures.

The performance degradation of High Temperature Superconducting (HTS) tape, which may be influenced by various heat exchange conditions due to different cooling methods, is of significant for HTS devices under repeated overcurrent. In this article, considering different heat exchange conditions, a series of repeated overcurrent experiments were carried on YBCO tapes under 50Hz sinusoidal alternating current. The degradation of critical current of YBCO tapes after repeated overcurrent was recorded. the resistance characteristics of YBCO tapes under different cooling conditions were analyzed. Through finite element simulation, the temperature and current distribution of YBCO tape under different heat exchange conditions were simulated. The experimental results show that the overcurrent capability of the conductor under conduction cooling is far inferior to the liquid nitrogen immersion method.

Nuclear magnetic resonance (NMR) probes using thin-film high temperature superconducting (HTS) resonators offer high sensitivity and are particularly suitable for small-sample applications. We are developing an improved 1.5 mm HTS NMR probe designed for operation at 14.1 T and optimized for (13)C detection. The total sample volume is about 35 μL and the active sample volume is 20 μL. The probe employs HTS resonators for (13)C and (1)H transmission and detection and the (2)H lock. We examine the interactions of multiple superconducting resonators and normal metal tuning loops on coil resonance frequency and probe sensitivity. We test a recently introduced (13)C resonator design, engineered to significantly increase (13)C detection sensitivity over previous all-HTS probes. At zero field, we observe a (13)C quality factor of 6000 which is several times higher than previous resonators. In this work the coil design considerations and probe build-out procedure are discussed.

This paper presents a 14-pole dual-band high selective high temperature superconducting (HTS) filter including two narrow notches. A flexible half-wavelength resonator, two cross-coupling structures and a novel feeding structure are proposed and analyzed successively. The HTS filter is fabricated on a 2-inch-diameter double-side DyBa2Cu3O7 HTS thin film with a 0.5-mm-thick MgO substrate and measured with a low-temperature test system at 65 K. The measured results show that the filter has 1 dB passbands of 1363–1440 MHz and 1490–1566 MHz, respectively. The filter has two narrow notches with maximum notch depths of more than 30 dB. Due to the cross-coupling structures, five transmission zeroes are located at both sides of the two passbands, which further improve the selectivity of the filter. The measured results are in good agreement with the simulated ones.

High temperature superconductors (HTS) enable very compact electric machines with high power density. The aim of this paper is to study and improve an HTS power generator based on the authors' previous 10 MW double claw pole design. An additional stator was added to the machine, increasing the copper volume in the generator, resulting in a large increase in power density. Furthermore, with the additional inner stator, the overall current density in the individual stators can be reduced, leading to an increase in efficiency. The modularity of the generator is further improved through the addition of the third stator, further increasing its fault tolerance. The efficiency of the machine can be increased from 94.5% to 95% at a power output of 11.5 MW or through a further reduction of the current density in the stators, an efficiency of 95.6% can be reached while maintaining a power output of 10 MW. Hence, the newly proposed design offers a potential increase in power density, efficiency and modularity while maintaining the same machine diameter and low HTS tape requirements, making the design a very cost‐effective option to enable 10 MW direct‐drive wind turbines.

The alternating current (AC) loss is a key consideration of the operation economy and stability of the high temperature superconducting (HTS) cables. In this paper, the sources of the AC loss in the HTS cable are analyzed firstly. The three-phase HTS cable, adopted in the 35 kV km-level HTS cable demonstrating project in Shanghai, China, is modeled by the finite element method (FEM) to calculate the AC loss by the COMSOL Multiphysics. The AC loss of the designed 35 kV HTS cable is 1.31 W/m. The theoretical calculation method is also implemented to verify the modeling results. Furthermore, considering the on-site conditions of the demonstrating project in Shanghai, China, the calorimetric method is conducted by measuring the temperature difference between the inlet and outlet of liquid nitrogen. The obtained results provide useful indications for the future design and research of HTS AC systems.

With the gradual complexity of the high temperature superconducting (HTS) applications, the calculation model of large-scale devices is time-consuming. A semi-homogeneous modeling method based on the T-A formulation is proposed to study the electromagnetic characteristic of HTS magnet. Compared to the homogeneous model, the proposed model can improve the calculation accuracy without compromising speed. The model in this paper is beneficial to the design, rapid optimization and evaluation of the HTS magnet.

The 35-kV km-level domestic high-temperature superconducting (HTS) power cable project in Shanghai, China, is expected to be deployed in 2021. Facing the complex operating environment in the metropolitan area, such as the vibration excitation from the subway, pile driving, and seismic activities, the vacuum degree, sealability, and insulation performance of the HTS cables may be affected by the unavoidable mechanical perturbations. The response to the potential vibration excitation is a key factor for the safety and stability of the HTS cables in operation. Therefore, this paper conducts a set of vibration testings for the HTS cable under four kinds of vibration conditions, which include the subway vibration, pile-driving vibration, typical earthquake vibration, and Shanghai artificial wave vibration. Results show that the leakage and outgassing rate of the HTS cable is 1.3×10−6 Pa m3/s at a static state, and increases to 1.4×10−6 Pa m3/s after the vibration testing. The HTS cable exhibits insignificant changes after the vibration testings in the dielectric spectrum examination. The HTS cable can keep its function after the vibration testing that possibly occurred in the metropolitan area.

High temperature superconducting (HTS) synchronous machines are compact and light weight machines with higher torque to weight ratio, lower noise and better dynamic response for strategic and critical industrial applications. The development of HTS field coil is one of the main technological challenges in realizing the HTS synchronous machines, as it involves the selection of HTS tape, winding technology, handling of the HTS tape while winding on a winding machine and testing of the developed HTS coil at desired cryogenic temperatures. With advancements in HTS tape technology, recent 2G HTS tapes are offered with higher engineering current densities with respect to 1G HTS tapes even at higher magnetic fields. Hence, the replacement of 1G HTS field coils of previously designed 200 kVA HTS synchronous machine with 2G HTS field coils at the same operating cryo-temperature shows a potential to enhance its capacity to 350 kVA (more than 75% increase in machine output). In the present work the details of design, development and testing of a double pancake type 2G HTS field coil are presented for capacity enhancement of earlier 1G based 200kVA HTS synchronous machine.

The design considerations of AC machines with windings made of high-temperature superconductors (HTS) are presented in the following paper. The considerations were narrowed to permanent-magnet excited machines, although the results can be extrapolated to many other machine types as general guidelines. The influence of basic machine parameters and coefficients during the design of such machines are considered in order to estimate operating conditions of HTS windings. The number of poles, number of slots or slot dimensions, coil placement, and arrangement, are taken into account with the intent to fully utilize features of superconducting materials such as the capability of conducting high current density without significant losses. The attention is placed on low power machines, below 1 kW, operating at liquid nitrogen temperature (77 K). For analysis purposes, the finite element method (FEM) is used to calculate the distribution of the magnetic field and its effect on the critical current of the HTS coil. The numerical analysis is carried out in ANSYS software.

The search for superconductors with high values of the critical temperature has started shortly after the first observation of the phenomenon in 1911. At present, there are several paths towards reaching this goal. Here we focus on the direction based on observing high temperature superconducting state in some metallic nanoclusters. The macroscopic high Tc superconducting current can be provided by the Josephson tunneling between such clusters.

High temperature superconducting (HTS) cable, with significant low dissipation and massive current carrying capability, is a promising solution for the shortage of transmission capacity in mega-cities. China Southern Grid launched a HTS cable project in 2017 to develop a medium voltage concentric HTS cable system for installation in the distribution grid at urban area in Shenzhen City. It is the first time that concentric HTS cable system is developed and will be the first HTS cable installed in urban grid in China. The cable core mainly consists of three concentric phases winded by YBCO tapes and cold dielectric insulations in between phase-to-phase, phase-to-former, and phase-to-screen. The cable has a rated voltage of 10 kV and a rated current of 2.5 kArms. The critical current ( $I_{c}$ ) is at least 6 kA per phase. The outline diameter of the cable core is 76 mm and the cryogenic pipe is 175 mm. As a middle step, we designed and manufactured a 30 m long prototype cable system and it was tested generally according to IEC 63075. For improvement of the manufacture processes, several short cable core samples were made, tested, and dismantled. The ultimate goal of the 30 m prototype is to verify the design and accumulate experience for the installation of the 400 m fully functional cable system in the grid. The test results of the 30 m cable prototype are presented and discussed. The 400 m class HTS concentric cable demonstration project has already started and it is expected to energize in grid in late September, 2021.

In this article, the operating current and torque of surface-mounted permanent magnet (SPM) wind power generators with high-temperature superconducting (HTS) armature windings are analyzed. The influence of coil location and current angle on the electromagnetic performance is investigated systematically. The results show that the location of the HTS coils significantly affects the operating current and torque. Furthermore, the maximum torque current angle of SPM wind power generators with HTS armature windings can be different from 180° due to the interaction between the armature and magnet fields. A design optimization method for wind power generators with HTS armature windings is developed in this article. The optimal design is then identified with consideration of the coupling influence of coil location and current angle.

With the discovery of high-temperature superconducting (HTS) tape and the improvement of the performance of the second-generation HTS tape, the application of superconductors in power system is gradually unfolding. There have been many demonstration projects at home and abroad. When the HTS tape is applied to the power cable, the mechanical external action of the cable winding, laying and installation operations, and the Ampere force when the current is applied are applied to it. Stress has an important influence on the critical current characteristic of the superconducting tape. In different application scenarios of the tape, different materials and thicknesses reinforcement layers can be chosen. In this paper, for the YBCO superconducting tapes with different reinforcement layers, a set of systems with critical current under tensile stress at cryogenic temperature is used to study the influence of tensile stress on the critical current of superconducting tape at low temperature. We analyze the influence of the structure of the superconducting tape on the characteristics of the tape and studied its degradation characteristics, which have guiding significance for the design and operation of the superconducting cable.