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High-temperature superconductor (HTS) materials, including HTS wires and bulks, become available to apply in transportation applications such as various hybrid levitation and linear propulsion systems. In this paper, for the evacuated tube transportation and electromagnetic aircraft launch system applications, two different types of hybrid HTS levitation and linear propulsion systems have been designed and modeled, respectively. The levitation force and electromagnetic thrust performance of the systems have been studied by a numerical and finite element method. With the principal parameters’ verification, this work forms a basis for the structural and electromagnetic design of a hybrid HTS levitation and linear propulsion systems for practical hyper flight applications. [ABSTRACT FROM AUTHOR]

High temperature superconductor (HTS) is becoming more and more attractive for the application in high field magnets, which can be utilized in the magnetic resonance imaging (MRI) and rotating machines. To charge the HTS magnets and operate them in persistent current mode, a persistent current switch (PCS) is very necessary. This paper will focus on how to build a fast persistent current switch controlled by ac magnetic field. The PCS can present a large resistance rapidly compared with conventional PCS and recover to zero-resistance in a short recovery time. Impacting factors and strategy to control the proposed PCS are discussed. An experimental system is built and tests are carried out to verify the practicality of the proposed PCS. [ABSTRACT FROM AUTHOR]

High-temperature superconducting magnetic bearings can be suspended without contact and self-stability. They are widely used in many industries. Before the actual production of magnetic bearings, the structural design and parameter optimization are very important. The design and optimization method of radial high-temperature magnetic bearing are studied in this paper. The force calculation expression was deduced. The bearing capacity of high-temperature magnetic bearings was optimized. The performance of the radial HTSMB was analyzed and verified by FEM. [ABSTRACT FROM AUTHOR]

The ac loss calculation problem is the key issue for a superconducting magnet. The existing numerical models do not consider the magnetic properties of the substrate while calculating the transport ac loss of high temperature superconductor (HTS) coated conductors. In fact, the unacceptable time and memory consumption makes the ac loss calculation a tough task while considering the magnetic properties of the substrate. This paper introduces a two-dimensional multiscale method for calculating the transport ac loss of HTS YBCO coated conductors with magnetic substrate, which can greatly reduce the calculation time under the premise of high accuracy. The multiscale method is realized with three unidirectionally coupled models and only considers the nonlinear E–J characteristics in two simple models with fewer degrees of freedom, which avoids considering the E–J characteristics in the whole coil. The calculation accuracy of the multiscale method is validated by comparing the simulation results with that of Ainslie's model with the same coil structure, which consists of 2 × 50 turns of YBCO tapes with ferromagnetic substrate. The results of the multiscale method model are highly consistent with that of Ainslie's model. The calculation speed can be increased by two orders of magnitude with the multiscale method, which indicates that this method is an effective approach to handle the transport ac loss calculation problems while including the ferromagnetic substrate. It also has the ability to solve much more complex problems in the future, such as large-scale HTS magnet. [ABSTRACT FROM AUTHOR]

This paper investigates the conditions of use and the equivalence of various constitutive laws used to model the electromagnetic behavior of high-temperature superconductors: two versions of the critical state model (CSM), the power law model, and a so-called percolation model. All these models can be used to represent the same superconducting material with some limit of accuracy. The CSM and the power law model are well known in the literature. The percolation model can be seen as a generalization of the power law model that includes also a CSM-like behavior at very low electric fields. The investigation has been carried out for three types of operating conditions: the sudden application of a dc excitation, a pure ac excitation, and combined dc and ac excitations. The equivalence between the different constitutive laws is shown to be a function of the magnitude of the electric fields and of the time scales involved. In the dc case, long time scales and very small electric fields are predominant; thus, the superconductor requires a model that is accurate at low electric fields, such as the percolation model. The losses then arise from the relaxation of the magnetic field in the sample. In the ac case, the power law and percolation models are nearly identical when considering power frequencies, so choosing the simpler power law model is fully acceptable in practice. In addition, the CSM coincidentally provides good predictions of the losses in the power frequency range. In the dc+ac case, when time scales in the range of minutes to hours are considered, it is shown that ac losses dominate over relaxation losses, and the same conclusions as for the ac case apply. [ABSTRACT FROM AUTHOR]

Synchronization properties of model systems containing large numbers of phase oscillators have many potential biophysical and other applications. Biophysical examples include networks of pacemaker cells in the heart and suprachiasmatic nucleus of the brain. In physical systems, the phase dynamics of high-Tc superconducting materials continue to attract attention, since systems of intrinsic Josephson junctions form natural arrays of coupled phase oscillators. As such, they have the potential to act as systems in which various exotic synchronization effects may be observed. In this paper, we make a more detailed exploration of the parameter space containing regions of spontaneous chaos synchronization in the CCJJ + DC model of intrinsic Josephson junctions. Extensive regions of phase synchronization-corresponding to the Shapiro steps with zero charge density in the S-layers-are found through numerical simulation. By computing the Lyapunov exponent spectra, we see that the spontaneous chaos synchronization occurs within certain subregions that overlap with uncharged steps in the IV-characteristics. We tried to stabilize the spontaneous chaos synchronization over a wider range of parameters, by applying a global, noninvasive, and proportional control scheme. The control is affected by applying a time-dependent phase shift to the external electromagnetic radiation, proportional to the total voltage. The effect of the control is found to be three-fold. First, it tends to broaden the current interval over which lower harmonic Shapiro steps occur. Second, it does not change the width in the current range over which the chaos synchronization occurs. Third, it makes the chaos synchronization more robust to thermal noise. The chaos synchronization we report here may be useful in any applications requiring more powerful, high-frequency, and chaotic signals, such as in secure communication. [ABSTRACT FROM AUTHOR]

For ground-based electromagnetic methods in geophysics dc superconducting quantum interference devices based on high-temperature superconductors are well suited as magnetic field sensors. Therefore, we introduce in this paper an advanced fabrication technology for high-temperature superconducting dc SQUIDs based on step-edge Josephson junctions. The dc SQUIDs are prepared on structured magnesium-oxide substrates. A trilayer of YBa2Cu3O7-x/SrTiO3/YBa2Cu3O7-x is deposited by pulsed laser deposition and structured with ion beam etching. The galvanometer-type design consists of four different dc SQUIDs directly coupled to a pickup loop. They exhibit large Ic Rn products and a voltage swing of more than 30 μV. The magnetic field noise amounts to about 20 fT/Hz1/2 and 35 fT/Hz1/2 for the white noise region as well as 25 fT/Hz1/2 and 100 fT/Hz1/2 at 100 Hz for ac-bias and dc-bias SQUID electronics, respectively. The advanced fabrication process thus enables to produce HTS dc SQUIDs intended for the use in geophysical applications with high throughput. [ABSTRACT FROM AUTHOR]

In this paper, a field coil is optimized for a kW-class high-temperature superconducting (HTS) generator prototype to decrease tape consumption and improve the use efficiency of the HTS tapes by increasing the operating current. First, the structure of the field coil is preliminarily designed based on a novel graphic method. Then, the field coil is optimized by using a genetic algorithm to decrease the tape consumption. Finally, the field coils are fixed in the finite element method generator prototype to study and compare the electromagnetic characteristics. The current distribution is calculated based on the Jc-B-θ characteristics, and the minimum current to determine the operating current is also derived. After the optimization, the electromagnetic characteristics are improved and the operating current is increased. [ABSTRACT FROM AUTHOR]

High temperature superconductor (HTS) is becoming more andmore attractive for high fieldmagnets. To charge the HTS magnets and operate them in persistent current mode, a persistent current switch (PCS) is necessary. This paper will focus on how to build a fast persistent current switch which can present a large resistance and with short recovery time. Impacting factors and strategy to control the PCS are discussed. An experimental system is built and tests are carried out to verify the practicality of the proposed PCS. [ABSTRACT FROM AUTHOR]

The YBCO Roebel cable is a promising option for the high-energy accelerator magnets and tokamak devices with high-current carrying capability and compactness. Referring to the complex current sharing and normal zone propagation, it is difficult to apply the traditional superconductor quench measurement methodology to such a long Roebel cable (2 m) in an adiabatic condition. An alternative method for the quench measurement is to make a Roebel pancake coil cowound with ribbon fiberglass. This paper starts reporting the methodology to wind the coil with impregnation process and the wire installment for the quenchmeasurement. Some initial performancemeasurements and a first trial of the quenchmeasurement were processed in LN2 at 77 K to show the robust performance of this Roebel cable at all the current contacts while maintaining the cable effectively adiabatic or similar to real magnets. [ABSTRACT FROM AUTHOR]

A high-temperature critical superconductor (HTS) dipole magnet relying on 12-mm REBCO tapes was built at CEA Saclay in 2016. Magnet studies had been started in the framework of the EuCARD High FieldMagnet program and continued within a collaboration agreement between CEA-Saclay and CERN. The final goal is to generate 5.4 T at 4.2 K in the 13-T background field of the FRESCA2 Nb3Sn dipole magnet. The HTS winding is made of three double-layer racetrack-type coils, wound from a stack of two double-layer REBCO tapes, stabilized with beryllium copper ribbons. Before it is installed inside the aperture of FRESCA2, at CERN, themagnet has been tested at CEA-Saclay in the standalone mode. In this paper, after a brief recall of the magnet design, we will report on the magnet manufacturing and the first powering tests results. [ABSTRACT FROM AUTHOR]

In this paper, the charging characteristics of high-Tc superconducting (HTS) field coils are analyzed experimentally to verify the efficiency of using HTS contactless rotary excitation devices (CREDs). The HTS CRED is composed of eight HTS rotor strands, which are connected in series with HTS load coils, and eight neodymium permanent magnets (N50). The magnetic field of N50 is approximately 0.14 T when the air gap between the HTS rotor strand and N50 is 8 mm. In order to verify the proper charging method, two types of experiments are performed. In the first experiment, the HTS loads are connected in series and are charged by eight HTS rotor strands of the HTS CRED. In the second, the HTS loads are located along the same axis, and each coil is charged by four HTS rotor strands of the HTS CRED. In these experiments, the currents flowing through the HTS loads are measured for rotor speeds ranging from 50 to 300 r/min. [ABSTRACT FROM AUTHOR]

The high strength conductors used in pulsed magnets in the US National HighMagnetic Field Laboratory (MagLab) are manufactured from Cu matrix composites. One of the composites is made from particle-reinforced Cu. The fabrication of these composite conductors requires high deformation strain, which creates high densities of dislocations and reduced particle spacing. Both mechanical strength and electrical conductivity can be predicted from particle spacing and dislocation density. When dislocation density reaches a certain value, the particle size, distribution, and shape become important to mechanical properties. We studied the particle size, distribution, and shape in high-strength conductors with respect to the properties of the conductors. The two most important factors related to the above parameters were dislocations near the interface between particle and matrix and stress concentration near the particles. By engineering these variations, the properties of the conductors can be optimized. This paper reports our understanding of the relationship between critical properties and particle distribution in composite conductors for high field pulsed magnets. [ABSTRACT FROM AUTHOR]

Quench detection for the high-temperature superconducting tape, especially rare-earth barium copper oxide (REBCO) tape, is difficult due to the small normal zone propagation velocity in it. To address this issue, we have proposed a novel quench detectable REBCO tape with a low-temperature superconducting wire used as a quench detector, "REBCO/LTSd tape." In this paper, we numerically and experimentally demonstrated the validity of the tape consisting of the yttrium barium copper oxide (YBCO) tape and the Nb-Ti wire used at 4.2 K under no external field. Results of the numerical simulation showed that sufficiently high voltage of 0.1 V can be detected before the maximum temperature of the YBCO tape reaches 50 K with the Nb-Ti wires having high resistance at normal conducting state. Experimental results also demonstrated that the quench in the YBCO was detected with the 1 V scale voltage by using the pure Nb-Ti wire. [ABSTRACT FROM AUTHOR]

This paper investigates an optimal design methodology for multiwidth (MW)high-temperature superconductor (HTS) magnets, where pancake coilswound with the narrowest tapes were placed at and near the magnet center and those with progressively wider tapes toward the top and bottom of the magnet. For a given design, target of field strength and winding bore, input parameters include tape width, number of grading tapes, and number of pancakes coils, while the main objective is to minimize the magnet volume, i.e., essentially the stored energy and thus the cost. A magnet with a single-width tape is also designed as a control sample for comparison. A case study on a design of 3-T 240-mm HTS magnet was carried out. In that case, MWmagnets save 40% wire consumption of single-width magnets. The results are expected to be beneficial to determine the practical level of HTS tape grading and estimate a volume of an MW magnet. [ABSTRACT FROM AUTHOR]

High-efficiency high-temperature superconducting (HTS) induction heating equipment has been regarded as a promising application for thermal processing of metal material, in which an HTS magnet generates a high magnetic field to form the background field in the iron core and the rotating billet is heated by eddy current to process temperature. Efficiency analysis for the traditional induction heating and new structures for the HTS induction heating are studied in this paper. A new type of superconducting induction heatingmagnet structure is proposed. Through the parallel connection of multiple magnetic circuits, it can make more effective use of the high magnetic field produced by superconducting magnets. The applicable range and application criterion of the new structure are also given. Calculation models for induction heating system electromagnetic field and billet region temperature field analysis are established. The megawatt (MW) class conductioncooled Yttrium Barium Copper Oxide (YBCO) magnet system is designed. The magnet consists of an iron core andHTS coils wound with the spliced YBCO-coated conductors. The magnet system is cooled by two AL325 GM refrigerators and the operating temperature is 20 ~ 30 K. Furthermore, the prototype YBCO coils with the same thickness are fabricated and tested in the LN2 . Test result of the prototype magnet is presented. [ABSTRACT FROM AUTHOR]

Quench protection is the elephant in the room, when it comes to high temperature superconducting (HTS)magnets. For many HTS magnets, quench protection has not been much of a problem, because the stored energies of the magnets have been low compared to low temperature superconducting magnets. The principles of quench protection are the same regardless of the type of superconductor used. In general, a quench is not a problem if the adiabatic hot spot temperature at the end of the quench is less than a temperature that damages the conductor or its insulation and the magnet voltages are low enough not to breach the magnet insulation. It has long been understood that quench propagation along anHTS conductor is much slower than forNb-Ti. The reason for this is the large enthalpy change that occurs during a quench of an HTS conductor. The magnet quench characteristics are a function of the conductor current density, the local temperature margin, and the ratio of copper to noncopper in the conductor. With an HTS conductor one must add the effect of conductor field orientation that can affect both the critical current and the critical temperature. This paper explores ways for protecting magnets made from insulated rare earth (and Yttrium) barium copper oxide (ReBCO) tape or a similar HTS conductor that can be wound after reaction. [ABSTRACT FROM AUTHOR]

The rare isotope science project (RISP) was established at the Institute for Basic Science, Daejeon, South Korea to construct a heavy ion acceleration facility for rare isotope beam production. The separators include two pre- and main separators. The central purpose of the preseparator is to remove the primary and unwanted isotope beams; radiation heating and shielding are the major design considerations. For a warm ion, the hightemperature superconducting (HTS) dipole magnet will be used in the front region of the preseparator, and six HTS quadrupole magnets will be installed consecutively. In this paper, we present the electromagnetic design details and the specifications of the consecutive HTS quadrupole magnets for the preseparator at the RISP. Metal (Stainless steel 316) insulated magnets were designed to include iron cores. Using the finite-element method tool, six HTS magnets were modeled and simulated. The operational characteristics including the field gradient, effective length, and uniformity of each magnet were analyzed and presented as well. The research outcomes will be useful for the actual construction of a heavy ion acceleration facility in South Korea. [ABSTRACT FROM AUTHOR]

In this paper, a doubly fed doubly salient high temperature superconducting linear motor (DFDS-HTSLM) is proposed for vertical transportation. The proposed DFDS-HTSLM adopts a five-phase doubly salient configuration. The stator consists of iron lamination only with no windings or permanent magnets. The mover houses both the copper armature winding and the HTS field winding in its outer layer and inner layer, respectively. By using the HTS field winding, the air-gap flux can be flexibly adjusted by controlling the DC current flowing in it. In addition, by using five-phase configuration, the proposed motor can realize the fault-tolerance operation easily, hence improving the reliability. [ABSTRACT FROM AUTHOR]

Degradation of critical current (Ic) in a hightemperature superconducting (HTS) tape under bending conditions had been previously investigated. These investigations were focused on only either bending or torsion. A rotating flux pump is used to study the charging characteristics of an HTS synchronous motor. In order to design the rotating flux pump connected in series, the elliptical winding applied together with combined bending and torsion is essential. Therefore, in this paper, the critical current considering curvature of elliptical shape is measured with regard to nine kinds of mandrels. The shapes of the mandrels are a tall prolate ellipsoid, oblate ellipsoid, and semicircle. The diameters of each shape are 20, 30, and 40 mm, respectively. The experiments are mainly composed of three conditions: straight, bending, and combined bending and torsion. Finally, the experimental observations have been compared with the theoretical predictions. [ABSTRACT FROM AUTHOR]

This paper proposes an advanced method to satisfy both the stability and charging/discharging time constant requirements of second generation high-temperature superconductor (2G HTS) magnets. This novel method entails installing metal-insulator transition (MIT) material between the turns of the 2G HTS magnets. TheMIT material acts as an insulator when the temperature is lower than a certain value. Above this temperature, the MIT material becomes a conductor. This transition can be used as a switch between the turns of the 2G HTS magnets. We refer to this temperature-dependent smart switch as "smart insulation." Considering the operating temperature, we selected V2O3 as the material for smart insulation. We have experimentally verified that the advantages of both the insulation magnet (in the superconducting state) and no-insulation magnet (during quenching) can be simultaneously realized. [ABSTRACT FROM AUTHOR]

High-temperature superconductors (HTSs) are a strong candidate for high field magnets. As their properties are extraordinary, especially under high-fields and very low temperatures, there are many ongoing projects around the world. The NOUGAT project aims at building a 10-T insert operating inside a 20-T resistive background. Its objectives are not to reach a higher field than the already existing resistive magnets, but rather to overcome the main issues of using HTS above 20 T and pave the way toward full superconductive magnets at lower cost. REBCO coated conductor tape was preferred for the NOUGAT insert even if its implementation is still challenging. Both insulated and metal insulated (MI) coils have been considered for the NOUGAT project. Due to their self-protection behavior, MI windings have been selected for building the insert, but we are still investigating insulated coils for future applications. We built a fully-instrumented insulated single pancake wound with a 6-mm-wide tape. Voltage taps are set up on each turn to monitor the quench propagation in vapor helium up to 60 K under high magnetic field up to 19 T. This study aims at developing our understanding of the windings quench behavior and testing various quench detection procedures for future large-scale insulated applications. The present paper underlines the main results. [ABSTRACT FROM AUTHOR]

In the framework of the project where space in a cryostat is strictly limited, the high temperature superconductor (HTS) segments of the current leads have to be placed horizontally and in a scattered magnetic field. We developed the current leads optimization model for such conditions. In this paper, we present the results of optimization for 2000AHTS current leads, comprised of 2G HTS tapes and able to work in the magnetic field up to 2 T. The optimal parameters of the current leads segments have been determined using a numerical simulation. In order to approach the maximum efficiency, it is necessary to have a very good heat exchange between the current leads and evaporating helium gas. The impact of the external magnetic field on the heat leak from current leads into liquid helium is studied. [ABSTRACT FROM AUTHOR]

Inmany applications dipole magnetswith coils having significant curvature are needed. This is particularly challenging for high temperature superconductors (HTSs) as they are brittle. One possible application for curved HTS coils was the fragment separator dipole magnets for the Facility for Rare Isotope Beams (FRIB). For this application these magnets would operate in a high radiation environment and would be subject to a high heat load. Removal of heat generated in magnets in this environment using conventional Ni-Ti and Nb3 Sn superconductors, which generally operate at ~4.5 K, is difficult. However, an HTS conductor can be used to permit operation at 40Kwhere heat removal is significantly more efficient. As these coils are curved, one side of the coils has a reverse curvature requiring the development of special technology to wind the coils. As part of an STTR grant to develop and demonstrate a super-ferric design for a 2.2 T magnet, two curved coils were fabricated with a 12-mm-wide SuperPower ReBCO conductor and first tested in liquid N2 at 77 K. Afterwards the coils were installed into a cryostat and cooled to the design temperature of 48 K with cryocoolers. This paper presents the construction details and test results for these coils. [ABSTRACT FROM AUTHOR]

TheKarlsruhe Institute of Technology (KIT) agreed to construct and test the high-temperature superconductor (HTS) current leads for the tokamak JT-60SA presently under construction in the frame of the Broader Approach agreement between Europe and Japan. In total 6 HTS-CLs for 25.7 kA for the TF coils and 20 HTS-CLs for 20 kA for the PF and CS coils are needed. In addition, the acceptance tests of the HTS current leads were performed in the test facility CuLTKa at KIT. The manufacturing started in 2014 and the last current leads were tested in July 2017. The main parts of the acceptance test are the determination of the heat load at 4 K and the 50 K He mass flow rate through the heat exchanger as well as the simulation of a loss of flow accident. One test of the PF current leads also included a pulse test at 20 kA to demonstrate their PF operation capability. In this paper, an overview of the manufacture and acceptance tests of the HTS current lead is given. The results for the different current leads are summarized and compared to the specifications. [ABSTRACT FROM AUTHOR]

Based on two high-temperature superconducting pulsed power transformers, a double-module pulse power supply is presented and the collaborative discharge of the two modules is discussed in this paper. Seven discharge modes are compared and four evaluation criterions are used to evaluate the output current of the seven discharge modes. Simulation results show that three modes are proved to be feasible and can output a large rectangular pulse current with high amplitude and wide pulsewidth, while the other four modes are all proved to be unsatisfactory and not recommended. Relevant experiments on mode one and mode two are carried out and the results verify the accuracy and rationality of simulation analysis. [ABSTRACT FROM AUTHOR]

The China Fusion Engineering Test Reactor is a new tokamak device whose magnet system includes toroidal field (TF), central solenoid (CS), and poloidal field (PF) coils which are made up of cable-in-conduit conductor (CICC). The maximum field of CS and TF will reach around 15 T, which is much higher than that of present reactors. In this case, the high-temperature superconducting material Bi-2212 is considered as one potential magnet material for CICC because it has an outstanding conductor-carrying capacity at 4.2 K in magnetic field, especially for that with high-pressure heat treatment. However, Bi-2212 phase is a ceramic structure, which is sensitive to strain. The mechanical property is important for its application. In this paper, the axial tensile measurements on Bi-2212 round wires with different heat treatments were performed at room temperature, 77 K and 4.2 K, respectively. It was found that the wires with high pressure heat treatment had higher mechanical strength than that with normal pressure. The compared results were given, and SEM of cross sections for tested samples was also made and analyzed. [ABSTRACT FROM PUBLISHER]

Inductive pulsed power supply (IPPS) based on multiple high-temperature superconducting pulsed power transformer (HTSPPT) modules is a novel technology for electromagnetic launching. In a compact multimodule IPPS, the mutual couplings between HTSPPT modules are unavoidable. In this paper, an IPPS with the method of improved pulse-forming process which proved to be feasible by preliminary experiment is proposed to analyze the effect of the mutual couplings. The characteristics of the mutual coupling effect on the IPPS are presented in detail by theoretical analysis and parametric simulations. The evaluation indices reflecting performances of the IPPS under the mutual coupling effect are derived from simulations, including the energy storage capacity, flux linkage, axial tensile force, output current amplitude, and so on. Parametric simulations are executed with respect to the module arrangement, the number of modules, and the arrangement radius. Finally, the analysis of mutual coupling effect is summarized, and a strategy for exploiting mutual couplings between modules is put forward to improve IPPS performance. [ABSTRACT FROM PUBLISHER]

The MJ-class superconducting magnetic energy storage system (SMES) is most likely put into commercial utility applications. In China, several 1–100-MJ-class high-temperature superconducting (HTS) SMES projects are undergoing preresearch and conceptual design stage by the government and the power grid corporations, and these SMESs will be developed later. The configurations of commonly used SMES magnets are single-solenoid, multiple-solenoid, and toroidal magnets. Each configuration has its own electromagnetic and mechanical characteristics. In this paper, an optimal design and comparison were carried out to explore the suitable configuration for the MJ-class SMES magnet. As the critical current of the conductor is strongly influenced by the magnetic field and its applied direction, optimization of the HTS coil's configuration is required to minimize the length of the HTS wire. The optimization was conducted with the genetic algorithm and the finite-element method. In order to find the dependence of energy storage capacity on the wire cost, the magnet schemes of seven energy requirements were investigated. An optimal design is performed for the seven stored energies with the three types of magnet configurations. The comparisons between single-solenoid, four-solenoid, and toroidal coils are presented. The magnetic field and stress distribution of the SMES magnet are also depicted. [ABSTRACT FROM PUBLISHER]

High-speed rotatory electromechanical devices can be practically implemented using magnetic bearings that provide a contactless operation. Besides the contactless operation, high-temperature superconducting (HTS) bearings possess an exclusive feature, i.e., self-stability. This characteristic removes requiring any control schemes and consequently an easier implementation and lower costs would be expected. This paper deals with presentation of an optimal rotor configuration in radial-type HTS bearings. A semianalytical approach called Adomian decomposition method is used to efficiently solve the governing equations of HTS bearings deduced from the H-formulation combined with the E–J power law. Control variables of the optimization process include rotor dimensions as well as magnetization direction of permanent magnets. Optimization is carried out using a powerful approach called differential evolution with maximization of levitation force around the equilibrium position as its objective function. In order to verify the proposed approach, a two-dimensional axisymmetric finite element method is also implemented. [ABSTRACT FROM PUBLISHER]

This paper aims at assessing the potential of partially superconducting generators for 10 MW direct-drive wind turbines by investigating their performance for a very wide range of excitation currents. Performance indicators such as shear stress and efficiency and other generator characteristics are compared for 12 different generator topologies. To be sufficiently attractive, superconducting generators must have significant advantages over permanent magnet direct-drive generators, which typically have shear stresses of the order of 53 kPa and efficiencies of 96%. Therefore, we investigate what excitation is required to obtain a doubled shear stress and an efficiency of 98%. To achieve this, the different topologies require a range of excitation from 200 to 550 kAt (ampere-turns) with a low armature current density of 2 A/mm$^2$ . The more iron that is used in the core of these topologies, the easier they achieve this performance. By examining the maximum magnetic flux density at the location of the superconducting field winding, feasible superconductors can be chosen according to their engineering current density capabilities. It is found that high- and low-temperature superconductors can meet the performance criteria for many of the topologies. MgB $_2$ superconductors are feasible for the fully iron-cored topology with salient poles but need cooling down to 10 K. [ABSTRACT FROM PUBLISHER]

High-temperature superconducting (HTS) machines have the virtues of higher power density and better stability, which makes it a good prospect in the applications of wind power generation and ship propulsion. When the high-temperature superconductor is used in the rotating machines, the behavior of the conductor would be affected by the complex magnetic field, Lorentz force, and the centrifugal force. In order to evaluate the performance of the HTS coil in the machine, a finite element method model of the machine to calculate the magnetic field coupled with stress field was built in this paper. At first, the distribution of the magnetic field in the machine was calculated, then the Lorentz force was calculated and transferred to the stress field to obtain the stress and strain in the HTS and other structural materials. In the calculation, three operating conditions were considered, including no-load, full-load, and three-phase short-circuit fault. The results show that the stress on the HTS coil and the structural component are all smaller than the critical stress, which proves that the design is reliable. [ABSTRACT FROM PUBLISHER]

The coaxial magnetic gear is considered as a promising alternative to mechanical gearboxes. This paper proposes a novel single-permanent-magnet-array coaxial magnetic gear with only one layer of permanent magnets, which is stationary. The flux-modulating teeth are made of high-temperature-superconducting (HTS) material. Working principles of the proposed single-permanent-magnet-array coaxial magnetic gear are introduced analytically. A geometric optimization based on the ideal diamagnetic assumption of the superconducting bulks using the finite-element method is conducted to improve its torque capability. The performance is then evaluated by using the nonlinear E-J power law and compared with a single-permanent-magnet-array coaxial magnetic gear using ferromagnetic teeth. The result shows that the proposed topology can successfully magnify the input torque by a given gear ratio. The designed HTS-toothed single-permanent-magnet-array coaxial magnetic gear has a maximal output torque 1.73 times higher than its ferromagnetic-toothed counterpart. [ABSTRACT FROM PUBLISHER]

This paper presents regeneration characteristics of a 20-kW class high-temperature superconductor induction /synchronous motor (HTS-ISM). It has experimentally been demonstrated that the HTS-ISM generates synchronous electric power at about rated condition (20 kW), and the corresponding efficiency is more than 90%. The tested characteristics have also been reproduced based on the nonlinear electrical equivalent circuit. These results clearly show the possibility of highly efficient synchronous regeneration performance. [ABSTRACT FROM PUBLISHER]

Growing electricity demand from a range of sources and the changes of the power grid structures open the possibility of more frequent and much higher fault current. Traditional solutions to the fault are difficult to satisfy the requirement of the new power grid due to many factors, such as high cost, additional impact to power grid in normal loading condition, which leads to the research for an efficient alternative solution of interest to both academia and industry: Superconducting fault current limiter (SFCL). In this paper, two types of low-inductance solenoidal coils, the braid type and the nonintersecting type, are built with 2G high-temperature superconductors. The current limiting performance, the recovery characteristics, and the ac losses of both types of coils are tested and compared in detail. Experimental results show that both types of coils can effectively limit fault current and recover in several seconds. Furthermore, comparison between the ac losses of both types of SFCLs shows that the ac loss of the braid type coil is lower than that of the single tape by about an order of magnitude in low-current regions. [ABSTRACT FROM PUBLISHER]

Recently, high-temperature superconducting (HTS) generators are being studied to reduce the weight and size of large-scale gearless generators. However, the large-scale HTS generators have problems relating to high electromagnetic force because of their high current density and magnetic field. Therefore, the forces acting on HTS field coils should be considered as well as their support structures. This paper discusses the structural design of a module coil for a 12-MW class HTS generator for wind turbine. The 12-MW HTS generator module was designed based on electromagnetic analysis results obtained using the 3-D finite-element method. The detailed structure of the module coil was investigated considering the HTS coil bobbin, support, and cooling system. For secure design of the module coil, stress and deformation analyses were performed. Structural analysis results were compared with safety factors and critical yield stresses for each material. As the results, electromagnetic force and maximum stress of the module coil were calculated, and pole-type supports were found to be the most suitable for the 12-MW class HTS generator. [ABSTRACT FROM PUBLISHER]

Due to the self-protecting feature, no-insulation (NI) high-temperature superconductor magnets have been regarded as a reliable option to generate high fields, yet their intrinsic charging delay still remains a major drawback. To apply the NI technique for actual high-field user magnets, however, postquench transient behavior of such magnets need to be fully understood, particularly the electromagnetic interaction among magnetically coupled subcoils. Recent publications have shown successful simulations of the transient behavior of a single NI coil or a multicoil magnet using distributed network models. Even though these approaches are very accurate, they often require substantial computation time, especially when multiple iterations are required during design or analysis of an NI magnet having a large number of coils. This paper presents a simple circuit approach that may be effective for quench simulation of multicoil NI magnets. Each NI subcoil in a magnet is lumped into a single inductor with a resistor in series and a resistor in parallel. This approach has allowed us to simulate the whole magnet system within reasonable time without compromising the understanding of mutual interactions of all of the subcoils after quench, namely change in parameters such as voltage, current, and temperature with respect to time and coil to coil normal zone propagation in an electromagnetic manner. We verified the proposed approach by analyzing the quench process in a previously built 7 T, 78 mm all-REBCO NI magnet (by MIT), and by doing the first ever comparison between the simulated results with the data measured from actual experiment. [ABSTRACT FROM PUBLISHER]

With the development of high temperature superconducting (HTS) maglev stepping in a key period of test line applications, the test and analysis of the dynamic operation parameters become more and more crucial. In this paper, the dynamic operating characteristics of single-cryostat and multicryostat levitation systems were comparatively studied on a 45-m-long permanent magnet guideway test line with different working conditions. Vibration acceleration signals of three levitation systems (a single cryostat, a bogie with two cryostats, and a car with four cryostats) were measured in the running experiments. The vibration characteristics were analyzed in both time domain and frequency domain. Results show that the multicryostat levitation system has better dynamic performance of stiffness than those of the single-cryostat system. The experimental data also indicates a positive correlation between the stability of the HTS maglev vehicle and the number of the cryostat. This work is helpful to understand the essential characteristics of HTS maglev vehicle system, and will be beneficial to the future design. [ABSTRACT FROM PUBLISHER]

A 1-MW industrial-scale high-temperature superconductor (HTS) dc induction heater is being designed and manufactured in Shanghai Jiao Tong University, China. This paper is to present the design and engineering analysis of a HTS magnet with iron yoke for this heater. This magnet is to generate a 0.5-T dc magnetic field in the iron's air gap, where the billet is rotated. To enhance the thermal stability, the no-insulation (NI) coil and metallic insulation (MI) coil (co-wind with stainless steel strips) is introduced to the magnet. The influence of the NI&MI technique on the magnet's ramping process is analyzed. A significant ramping delay occurs on both the NI and MI magnet. Joules losses are generated by the current “bypassing” through turn-to-turn contacts, which may lead to significant temperature rise on the coils. Higher ramping rate often means faster ramping process and higher temperature rise induced by ramping loss. The MI magnet shows a much shorter ramping time and lower ramping loss than its NI counterpart, due to higher turn-to-turn resistivity. The MI coil is more suitable than the NI coil for this large-scale magnet. [ABSTRACT FROM PUBLISHER]

A general high-temperature superconducting synchronous motor (HTSSM) is designed and manufactured with an air-core structure, which eliminates the laminated iron core to concentrate the linkage flux in conventional rotor and stator. In an air-core structure, a nonmagnetic material such as glass fiber-reinforced plastic (GFRP) is used as an armature winding supports to avoid saturation of magnetic field density in the stator core and to reduce the weight and harmonics of the motor. However, GFRP air-core supporters make heat dissipation difficult due to the very low thermal conductivity of GFRP, which makes sustainable and stable operation of HTSSMs impossible. Therefore, in this paper, the concept of advanced air-core stator (AACS) is presented to enhance the cooling performance of a conventional GFRP air-core stator. The AACS concept pertains to the introduction of thermal conductive materials on an armature supporter to replace the GFRP material of a conventional air-core stator. The AACS concept structure for a 1.5-MW-class HTSSM was designed and analyzed using three-dimensional electromagnetic and thermal finite element method. [ABSTRACT FROM PUBLISHER]

Most high temperature superconducting (HTS) devices have been established by employing a single tape or a few tapes in parallel. These HTS devices generally have large current carrying capacity at present. Therefore, a cable with high current density becomes a key point for the application of HTS devices. In previous works, a core cable has been described and the thermal stability of the superconducting winding using the core cable is analyzed. In this paper, first the core cable is introduced which has a copper former and two conductor layers, internal layer and external layer. Subsequently, a finite-element analysis model of the core cable is built to analyze the electromagnetic characteristics of each conductor layer by taking seven design parameters into consideration: Cable A, Cable B, Cable C, Cable D, Cable E, Cable F, and Cable G with different pitch angle and twist pitch, and the structure parameters of the core cable are optimally designed on the basis of the electromagnetic characteristics analysis. Finally, the short core cable sample consisting of YBCO coated conductor with an outer diameter of 6 mm, and the critical current of about 500 A @77 K, self-field, and experimental platform are all made to verify the core cable design and analyze the changes of current-carrying features of the core cable along with the extra magnetic field. According to the results, when the core cable is applied in HTS devices (such as HTS transformer), extra magnetic field intensity of the core cable is better to be less than 0.1 T. [ABSTRACT FROM PUBLISHER]

High-temperature superconducting (HTS) materials, especially REBCO coated conductors (CCs), are promising for the application of high field magnets, current leads, and power devices. However, the current capacity is limited for a single CC. In recent years, several prototypes of cable, conductor, and strand were proposed and demonstrated in order to increase current capacity. Except for the high current capacity, the mechanical property is other one of the important factors in practical applications. This paper numerically analyzed the mechanical characteristics of a quasi-isotropic strand composed of four substrands by stacking ReBCO CCs in parallel, which mainly include dependencies of bending radii and twisting pitches on critical currents. The strain distributions of the strand in bending and twisting as well as combination of bending with twisting were calculated by the simulation method. The results are useful in application of high field and large-scale magnet and current lead in low temperature [ABSTRACT FROM PUBLISHER]

The development of high temperature superconducting (HTS) DC power cables requires a detailed information on the impact of the main characteristics of the cable architecture on the electrical parameters of the superconducting tapes. This paper presents the experimental dependence of the critical current and n-value of BSCCO-2223 and (Re)BCO commercial tapes on the cabling twist pitch. DC characterizations were conducted on single tapes twisted around an insulated multistranded Cu former from an actual HTS power cable having a typical diameter of 3 cm. For these characterizations, the twist pitch was varied from 5 to 25 cm. To check that permanent degradation occurred, the critical current Ic and the n-value were measured on a flat sample holder prior to conduct the twist pitch measurements on the former. The results can be used to determine the available range of wire twist pitches to help designing HTS DC power cables. [ABSTRACT FROM PUBLISHER]

High-temperature superconductor (HTS) technology has been studied recently for the use with superconducting high-power transmission and distribution, motors, generators, and fault-current-limiting devices such as cables and transformers. HTS technology, which can provide a large electromotive force in a small area owing to its large current density compared to that of a normal conductor, can reduce the weight and loss of a generator when compared to the attributes of a conventional machine. Moreover, once the HTS conductor has stabilized, the challenge of cooling the windings in large-scale generators can be resolved. Therefore, the technology has been studied for application with 10-MW-class superconductor wind-turbine generators. Although an HTS conductor generator offering a higher torque density, lower weight, and higher efficiency than a conventional generator can be designed, the design must satisfy the requirements of the critical magnetic field, critical current, and critical temperature of the superconducting winding. The HTS homopolar superconducting synchronous generators have a simple structure with a fixed HTS conductor and are one of the most suitable types of generator that is able to satisfy these requirements more easily. In this paper, we propose a 10-MW homopolar-type wind-turbine generator. [ABSTRACT FROM PUBLISHER]

This paper reports the feasibility of the impregnation of no-insulation (NI) high-temperature superconducting (HTS) coils using an electrically conductive epoxy resin. Recently, several studies of HTS coils without turn-to-turn insulation have been reported for field coils used in rotating machines such as motors and generators. The NI winding technique enhances the thermal stability of the HTS coil without requiring complicated protection techniques because the quench current is automatically bypassed through the turn-to-turn contacts within the HTS coil. Nevertheless, there is still a question as to whether the NI technique can be applied to rotating machines. To utilize an HTS coil under high mechanical loads such as field coils for rotating machines, the HTS tapes must be stabilized mechanically. For HTS field coils intended for use in rotating machines, epoxy impregnation is generally necessary to protect the HTS field coil from mechanical disturbances caused by the magnetic field and rotational vibration of the rotor to enhance the mechanical stability [1], [2] . However, the NI HTS coil cannot be fabricated by wet winding using epoxy resin because epoxy resins such as Stycast 2850 FT and CTD 521 are electrically insulating materials. This study examines the electrical stability of an NI HTS coil impregnated with an epoxy resin containing electrically conductive particles. The results are likely to present useful data for the application of electrically conductive epoxy impregnated NI HTS coils to rotating machines. [ABSTRACT FROM PUBLISHER]

With the aim of verifying the winding technology required for fixed-field alternating gradient (FFAG) accelerator magnets, and also to verify the magnetic field accuracy as compared with the designed field distribution, a reduced-size test magnet, referred to as a “model magnet,” has been developed. The model magnet was designed to incorporate multiple REBa2Cu3Ox (REBCO) coils with characteristic shapes, namely negative bend parts and 3-D winding shapes, derived from a full-scale spiral-sector FFAG accelerator design which was accomplished in this study. The coils were wound using 4-mm-wide REBCO-coated conductors made by the ion-beam-assisted deposition metal organic chemical-vapor deposition method, and the total length of the conductor for the model magnet was about 2000 m. After winding, the coils were installed in heat-conduction shells made of an aluminum alloy and were directly cooled by a Gifford-McMahon (GM) cryocooler in a vacuum vessel. It was essential to wind the REBCO coils without degradations, such as local delamination of the superconducting layer, because the voltage generated at such degraded parts frequently increases during operation, and eventually results in thermal runaway. The superconducting properties of all coils were verified before and after installing them in the aluminum shells. This paper describes the assembly of the REBCO coils, as well as testing procedures and test results of the model magnet. [ABSTRACT FROM PUBLISHER]

Future high-energy accelerators will need very high magnetic fields in the range of 20 T. The EuCARD-2 WP10 Future Magnets collaboration is aiming at testing HTS-based Roebel cables in an accelerator magnet. The demonstrator should produce around 17 T, when inserted into the 100-mm aperture of Feather-M2 13-T outsert magnet. HTS Roebel cables are assembled from meander-shaped REBCO-coated conductor tapes. In comparison with fair level of uniformity of current distribution in cables made out of round Nb–Ti or Nb${}_{3}$ Sn strands, current distribution within the coils wound from Roebel cables is highly nonhomogeneous. It results in nonuniform electromagnetic force distribution over the cable that could damage the very thin REBCO superconducting layer. This paper focuses on the numerical models to describe the effect of the nonhomogeneous current distribution on stress distribution in the demonstrator magnet designed for the EuCARD-2 project. Preliminary results indicate that the impregnation bonding between the cable glass fiber insulation and layer-to-layer insulation plays a significant role in the pressure distribution at the cable edges. The stress levels are safe for Roebel cables. Assuming fully bonded connection at the interface, the stresses around the edges are reduced by a large factor. [ABSTRACT FROM PUBLISHER]

Under transient operating conditions, especially in the case of alternating current or pulse current, the high temperature superconducting (HTS) magnet will suffer ac losses leading to changes in the temperature and critical current distribution throughout the magnet. A magneto-thermal model is needed to simulate this process. In fact, the state change of the magnet will lead to a nonlinear performance of the HTS magnet in the power system. This paper introduces a coupling simulation and modeling method for the HTS magnet based on a cosimulation model built in MATLAB and COMSOL. The HTS magnet element is a customized module created via the self-code S-Function in MATLAB. A magneto-thermal finite element model based on the PDE and Heat Transfer modules of COMSOL is built into the S-Function. This model allows the state of the HTS magnet to be monitored during the operating process. A small-scale HTS magnet including three single pancake coils with a dc excitation system is illustrated to verify the nonlinear characteristic of the HTS magnet and the effectiveness of this coupling simulation and modeling method. [ABSTRACT FROM PUBLISHER]

A current lead is a connecting device between the superconducting magnet and the power supply. A large amount of heat transfer ocurrs through the current lead because the cold-end in a superconducting system is thermally linked with the warm-end part. Therefore, high-Tc superconductor (HTS) is used in the current lead for a tokamak system. However, it is hard to consider the dependance of HTS's critical current with respect to temperature because the conventional HTS current leads consist of the HTS tapes with the same width and thickness, and their critical currents can differ from their temperature. For this reason, cold-end of the HTS section in current lead is designed excessively than necessary specifications. This generates the additional heat transfer between cold-end and warm-end within the HTS current lead. In this paper, a study on the HTS current leads with asymmetric structure is conducted to reduce the heat transfer by reducing the cross-sectional area of the HTS current lead. Asymmetric current leads are fabricated considering the design parameters about heat transfer within the HTS current lead. Current transporting tests on the conventional, symmetrical, and asymmetrical HTS current leads are performed to confirm the feasibility of the suggested design. And then, heat load of the asymmetric current lead is compared with the symmetric current lead. From this study, it is found that heat load of the current lead is reduced by using the asymmetric HTS current lead. [ABSTRACT FROM PUBLISHER]

This paper presents a study on the coil voltage of the no-insulation (NI) high-temperature superconductor (HTS) pancake coils during fast discharging operations. Fast discharging tests are performed on both a double pancake (DP) and an single pancake (SP) NI coil. The measured coil voltages are compared with that from an equivalent circuit model, which has been widely used in previous studies. A voltage pulse is observed on both the NI coils at the beginning of the fast-discharging operation. It is much higher than that from the modeling. The peak value of the voltage pulse increases linearly with the initial current. Comparison tests show that the coupling iron core has little influence on this coil voltage pulse though the inductance of the coils is enlarged seven times by coupling iron core. This coil voltage pulse shows that, during the fast discharging operation, the NI coil has a much higher turn-to-turn resistivity at the beginning stage than that in following process. Since the coil voltage pulse can be 600 times of the modeling estimation, it may be a potential risk to the coil protection system and measuring instruments. Therefore, special attentions are required on this aspect in the design of NI magnets. [ABSTRACT FROM PUBLISHER]