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This paper proposes a way to represent the anisotropic nonlinear superconducting properties using a discrete model for magnetization with the corresponding critical parameters, equivalent to the Power Law model for currents. This simplified model makes it possible to analyze magnetic systems with superconducting elements in a stationary mode, which reduces the calculation time. Using of proposed model is demonstrated by the calculation of force interactions between high-temperature superconducting (HTS) samples and permanent magnet in zero-field-cooling (ZFC) and field-cooling (FC) modes. HTS bulks in the form of a prism and stack made of HTS tape are considered. The calculation of the electromagnetic field was carried out using the method of integral equations for field sources. The data of calculations are compared with the results of experimental studies. [ABSTRACT FROM AUTHOR]

This is a follow-up study of the cryogen-free superconducting prototype generator with YBCO field windings. The previous paper had introduced the design of the structure, cryogenic system and electromagnetic characteristics of the prototype machine, whose operating temperature was 30 K, maximum field current was 100 A and rotating speed was from 10 to 30 rpm. In this paper, the optimization of the airgap magnetic field and the stability of superconducting magnet have been carried out. For the purpose of increasing utilization of the magnetic field of superconducting windings, its support structure and vacuum chamber of the cryostat had been upgraded in order to reduce the physical airgap between the armature teeth and the vacuum chamber room temperature wall from 10 mm to 2 mm. In addition, a new coil curing method, vacuum impregnation process with paraffin, had been applied while the YBCO coil fabrication, to improve its stability. The performance properties of the optimized system as well as the comparison between FEM simulation and experimental results are finally presented. [ABSTRACT FROM AUTHOR]

When a high temperature superconductor (HTS) coated conductor carries a DC transport current within the background of an oscillating magnetic field, the effect of dynamic resistance takes place. Under the circumstance when the dynamic resistance effect is significant, heat dissipation will be generated to change the temperature of HTS tapes. The amplitude of the instantaneous dynamic resistance increases with time due to the rising temperature. The phenomenon is more obvious when it comes to the HTS stacks where superconducting tapes are assembled so close. This paper proposes a numerical model with electromagnetic and thermal coupling to study the dynamic resistance of the series-connected HTS stack. Experimental results have shown that the proposed numerical model can describe dynamic resistance more accurately than conventional models. Besides, investigations are carried out on how the insulation thickness in the stack and the frequency of AC magnetic fields impact the dynamic resistance of HTS stacks under the influence of Joule heat. This can provide a useful reference for the design of superconducting devices in which dynamic resistance occurs. [ABSTRACT FROM AUTHOR]

In this work, we experimentally investigate the current carrying capacity of single REBCO tapes and stacks made 5 12 mm REBCO tapes with a 25 μm copper stabilizer in liquid helium in comparison with those made of bare tapes with no stabilizer at current ramp rates up to 55 kA/s. The motivation for the research was checking the usability of REBCO stacks as basic sub-elements for high current superconducting cables operating in fast cycling modes at 4.2 K. An original experimental technique was employed to induce the extremely high ramp rates. During the tests, one or 5-folded stacks curled into rings 95 mm dia with different types of joints were charged in the external magnetic field generated by an outer solenoid at ramp rates up to 1.6 T/s. The curled REBCO stacks were either soft-soldered over their entire length or contained local joints only. The maximum screening current induced in the samples during the outer solenoid charging Imax was registered. Our experiments showed that the current carrying capacity of the REBCO tapes and stacks was strongly affected by the absence or presence of the copper stabilizer as well as the type of the joint. The reasons for the Imax limitation for the copper stabilized and bare samples are also briefly discussed. [ABSTRACT FROM AUTHOR]

In recent years, the increase of microplastics (MPs) in ocean have been recognized as one of ocean pollution listed in Sustainable Development Goals (SDGs). Since MPs absorb harmful chemicals while floating in ocean, small fish which eats the absorbed MPs may fall into bad digestion and poor health condition. To solve the ocean pollution problem, a good MP collection method must be proposed with a high processing speed and a high MP collection ability. While, recently, the performances of 2nd generation high-temperature superconducting (HTS) magnets which can generate a field higher than 15 T have been improved. It is expected that MP collection performances are enhanced with such high field superconducting magnets. In this paper, we propose a conceptual design for MP collector from seawater using superconducting magnets. To evaluate the performances of the device, we developed a fluid simulation coupled with magnetic field simulation. The simulation results indicate that MPs can effectively be collected with a high magnetic field with a high processing speed. [ABSTRACT FROM AUTHOR]

For the design of superconducting magnets, the magnetic field and critical current distributions are usually calculated based on finite element software such as COMSOL, ANSYS, etc. These software are necessary for accurate structure modeling and field calculation, but they occupy large memory space and comsume long simulation time. Furthermore, they are not easy to use. To achieve an easy-to-implement solution for rapid magnet field and critical current calculations, this paper investigates three types of analytical calculating methods, and builds an autonomously-operated calculating application program (APP) for the uses in various superconducting magnets. [ABSTRACT FROM AUTHOR]

A simplified two-dimensional (2D) model, which takes the helical structure of the conductor on round core (CORC) cable into consideration, is utilized to analyze the electromagnetic and thermal properties of the cable. The model couples multi-physical fields through the JcBT(B,T) properties of the superconducting tape. We first introduced the modeling strategy and verified the validity of the 2D model. Then, considering the influence of thermal on the critical current of the tape, the cable loss under different conditions has been calculated. By changing the relative positions of the inner and outer conductor layers of the 2D model, the influence of the magnetic field on CORC cable loss can be obtained, and it can be extended to the periodic three-dimensional (3D) structure. [ABSTRACT FROM AUTHOR]

Based on existing quasi-isotropic strand (QIS) conductor and twisted stacked tape cable–cable in conduit conductor (TSTC-CICC), this paper proposed a novel QIS-CICC. The conductor was numerically modeled and the anisotropy of critical currents was analyzed. The simulations showed that although the critical currents of the QIS-CICC were worse than those of the TSTC-CICC for the self-field condition, the current decay of the QIS-CICC was far less than that of the TSTC-CICC under a 1 T external field, and the anisotropies of the two conductors were almost the same. [ABSTRACT FROM AUTHOR]

On the basis of 24 T magnet, the Institute of Plasma Physics, Chinese Academy of Sciences are developing 35 T all superconducting magnet. The magnet was designed as a combination of 20 T REBCO insert coil and a 15 T 150 mm low temperature superconductor background magnet. The 20 T insert coil consists of two coils nested together. NI winding technology is applied to coil 1 to increase its current density. The 50 μm thick Hastelloy tapes will be used to co-wind with REBCO tapes of the coil 2 to further improve its over-all mechanical strength. Electromagnetic analysis shows that the maximum ratio of operating current to the critical current of coil 1 and coil 2 is 0.63 and 0.37 respectively. A more accurate model for calculating strain considering screening current is under study. The inner joint is applied to the coil 1 to avoid in-plane bending of REBCO tape, and the detailed preparation method is given in the paper. The winding and preliminary testing of all double pancakes of coil 1 have been completed, and the winding of coil 2 is in progress. This magnet is planned to be assembled and tested in 2021. [ABSTRACT FROM AUTHOR]

This paper reports the feasibility of the impregnation of no-insulation (NI) high-temperature superconducting (HTS) coils using solder. NI coils are widely studied and used in many situations. To utilize an HTS coil under high mechanical loads such as field coils for rotating machines, the HTS tapes must be stabilized mechanically. Epoxy impregnation is a common method to protect the HTS field from mechanical disturbances caused by the magnetic field and rotational vibration of the rotor to enhance the mechanical stability. However, traditional epoxy resins are electrical insulating materials which might cause the turn-to-turn contact resistance of NI coils to increase. Therefore, we proposed a new kind of impregnation method using the electrically conductive material, solder. Two coils were fabricated and tested for comparison. One is the NI coil without impregnation and the other is the NI coil impregnated with solder. The charge-discharge and sudden-discharge tests were performed in liquid nitrogen at 77 K. The experimental results were studied with equivalent circuit analyses. The results of this paper could provide useful data for the application of solder impregnated NI HTS coils. [ABSTRACT FROM AUTHOR]

The large magnetic fields that bulk high-temperature superconductors (HTS) can trap, enable us to develop high specific power electric machines. However, very few bulk HTS machine prototypes have been developed worldwide. To explore the potential of bulk HTS machines, we developed a 30-kW low speed radial-flux synchronous machine comprised of a conventional stator with ferromagnetic teeth. The rotor has four-field poles. Each pole is a rectangular array of QMG melt-growth GdBa2Cu3O7-δ bulk superconductors. The poles are cooled by a 150 W capacity neon thermosyphon, which maintains an operating temperature of around 30 K. The drawback of the ferromagnetic teeth, however, is their saturation and core losses under high and variable magnetic flux. Apart from high flux above 1 T, the trapped field profile of bulk HTS poles exhibits a nonsinusoidal shape, the harmonic components of which increase core losses. Such core losses are normally divided into hysteresis losses and eddy current losses, both of which depend on the magnitude and frequency of the trapped field. Hysteresis loss is associated with domain walls movement, while eddy currents are circulating currents induced in the core. In this paper, core losses in a ferromagnetic stator of the 30-kW machine are determined while the poles are magnetized to 2 and 3 T. The results show that core losses increase with increasing magnetic flux and rotor speed. Core losses due to rotor pole fields at the operating speed of 190 r/min were 1.2% and 1.9% of the machine rated output under 2 and 3 T magnetization, respectively. Finally, the harmonic content of the machine output voltage was obtained. [ABSTRACT FROM AUTHOR]

The YBa2Cu3O7-x (YBCO) coated conductor (CC) is one of the most promising superconducting materials because of their high critical current (Ic) and low dependency of the Ic on the external magnetic field. For superconducting applications, a large number of joints are required to join relatively short YBCO CC tapes. In this paper, we study the electromechanical behavior of lap-jointed YBCO CC tapes fabricated by etching Cu stabilizer at its service temperatures (77 K) under self-field. The effects of etching Cu stabilizer on Ic and joint resistance (Rj) of YBCO CC tapes were discussed. The Rj was reduced and the Ic values of the joints are consistent with the parent CCs tape by etching the Cu stabilizer. Preferable electrical properties under applying axial tension are achieved and proved by the axial tension tests and finite element simulations. This fabrication technique is a unique practicable solution to reduce joint resistance for YBCO CC tapes with thicker metal stabilizing layers and improving electromechanical performance in second generation high temperature superconductor (2G HTS) devices. [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]

In this paper, an NbTi/BSCCO composite conductor made of NbTi/Cu wire and BSCCO/Ag wire cooled by cryocooler were investigated, extending the basic research on current distribution characteristics of low temperature superconductor and high temperature superconductor composite conductor and exploring its potential application. Current distribution characteristics with operating current, temperature, magnetic field, and current frequency were simulated and measured. Current-transfer characteristics between the two superconductors were also obtained. [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]

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]

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]

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]

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-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]

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]

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 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]

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]

The saturated-core-type superconducting fault current limiter (SCSFCL) is an important device to limit increasing fault currents in electrical power grids. However, there have been few numerical simulations carried out to simulate the properties of the superconducting DC coil in the SCSFCL, but such modeling is indispensable to the design and analysis of such devices. In this paper, a simulation method to simulate the SCSFCL with COMSOL Multiphysics is presented, and the AC losses of the DC coil in the normal, nonlimiting state, which is its usual operating state, are simulated and analyzed for the first time. A strategy to simulate the AC loss of the superconducting coil with a three-dimensional (3-D) model is given first. The nonlinear electric and magnetic problems are decoupled first. Next, the model is divided into smaller models for separate calculations. The 3-D model is further simplified into a 2-D model based on the worst case scenario for a conservative design. The AC loss distribution within the coil is given and the relationship between the AC loss and an AC component of the current is analyzed, and it is found that the outermost coil regions have much larger AC loss than the coils near the centre. [ABSTRACT FROM PUBLISHER]

Our project is to build a high-temperature superconductor (HTS) insert generating 10 T in its center and expected to work inside a 20 T background field. In the first step, the background field is provided by a resistive magnet to avoid major coupling issues. Nevertheless, the final goal is to have the insert operating inside an LTS magnet to yield a 30 T-class all-superconducting magnet. The insert is designed as a stack of pancakes and double pancakes wound with REBCO tapes. Preliminary tests are performed on a deposited polyimide insulated coil, although design has started with metallic-insulation coils. This paper presents results obtained on a double pancake insulated HTS coil that was tested inside both a resistive coil at LNCMI and a superconducting magnet at Tohoku University. The electrical and mechanical behaviors of the sample coil are discussed, and margins are estimated taking into account the field distribution on each point of the coil. Results are encouraging as the coil passes 370 A (82.9% lc) self-field and 260 A (68.6% lc) under 8 T. Moreover, the coil is still working even after the outer magnet quench. [ABSTRACT FROM PUBLISHER]

As part of a program that aims at developing design tools and technologies for dry MgB 2 magnets, a react-and-wind MgB 2 solenoid operating at 10 K and medium field range (1 up to 4 T) has been developed at CEA/Saclay. The prototype coil is wound from approximately 2 km of a commercial MgB2 wire and has a winding diameter of 200 mm, external diameter of 300 mm, and height of 200 mm. It has a nominal central magnetic field of 1 T and is placed in a 3 T background field generated by a classical NbTi magnet. The MgB 2 solenoid has been epoxy impregnated and then instrumented for low-temperature testing. The tests have been successfully performed with a nominal current of 100 A, an operating temperature of 10 K, and a background field of 3 T. Current sharing measurements have been carried out to compare the coil critical current to the bare tape critical current. In this paper, the magnet design, the manufacture, and the experimental results of the cryogenic tests are presented. [ABSTRACT FROM PUBLISHER]

AC loss is an unavoidable problem for a conduction-cooled HTS superconducting magnetic energy storage (SMES) magnet during dynamic operation, which may cause a temperature raise and affect the reliable operation of the magnet. In this paper, the anisotropic homogenization method is employed to realize the modeling of a 150 kJ hybrid SMES magnet based on H-formulation. The SMES magnet has a maximum of approximately 7000 turns. First, the homogenization method is validated that it can reasonably predict the ac losses of both YBCCO coils and BSCCO coils, but it has lower accuracy to estimate the ac losses of BSCCO coils than YBCO coils. Then, ac loss characteristics of the SMES magnet during dynamic operations are investigated. The magnetic field, current density distribution, and ac loss distribution are presented and discussed for different operation conductions. The results indicate that a steady-state current of less than 100 A may be an appropriate choice during power exchange for reducing ac loss. [ABSTRACT FROM PUBLISHER]

Various critical state models have been developed to understand the hysteresis loss mechanism of high-temperature superconducting (HTSC) films. The analytic relation between the hysteresis lossx and the remanent field was obtained based on Bean's critical state model for thin films in the full-penetration case. Furthermore, numerical calculation of local hysteresis loops was carried out by Kim's critical state model. In this paper, we investigated local hysteresis losses for a GdBCO coated conductor by using low-temperature scanning Hall probe microscopy and reproduced the experimental results by applying the critical state model. Because of the demagnetizing effect in thin films, analysis of local hysteresis losses can be useful approach to understand of total hysteresis losses. [ABSTRACT FROM PUBLISHER]

A coaxial cable made out of helically wound 2G HTS tapes is being widely implemented based on its low critical bending radius, ease of manufacturing and installation. Though the design technique is mature, the cable still lacks standard Ic definition. With increased usage of such cables, robustness in its operation is expected. HTS tapes are highly sensitive to externally applied mechanical stress and strain values. These limitations force the coaxial cables to be operated at 50–75% of its rated capacity. One of the major problems in coaxial cable design is the contact resistance of the tapes with the terminal, which affects the current distribution among different tapes in the same layer. Further current redistribution at constant intervals helps the applied current in bypassing the localized faults in the individual HTS tapes, thus making efficient use of the major length of the tape. This paper proposes the use of voltage shunts between HTS layers at constant intervals for regular current redistributions along the length of the cable. This method significantly helps to sustain the Ic value of the cable, even if it has got several minor defects in the tapes. [ABSTRACT FROM PUBLISHER]

Critical current and ac loss of high-temperature superconducting (HTS) tapes are two important factors for the application of ac HTS power cables. Generally, the current in the dc HTS cable is a combination of main dc current and ac ripple current due to the use of rectifier. The ac ripple current distribution without proper adjusting would be nonuniform in each layer especially when the dc HTS cable layer increases; it may lead to high ac loss and poor transmission capacity. In order to understand the ac ripple current sharing among dc HTS cable layers, the inductance matrix of the cable layers was deduced based on the geometry configuration of a self-shielding dc HTS cable. In this paper, in addition to the uniform current design principle, a self-shielding dc HTS cable is also designed with the HTS tape arrangements of each layer optimized by taking the ratios of ac ripple current amplitude to critical current in each layer as equal for minimizing the ac loss. According to the design configuration and deduced inductance matrix, current in each layer and ac loss are calculated. The results show that it is necessary to use the optimized design in the dc HTS cable design and the equal ratio design is better than the uniform current design. [ABSTRACT FROM PUBLISHER]

We developed a method to combine parallel superconducting HTS tapes to a current carrying element with high current and uniform current distribution among strands at ac mode. The current carrying elements are made of several parallel HTS tapes placed side-by-side on a round mandrel. The test of the small model made of five parallel 2G HTS tapes confirmed the idea. The method was implemented for 10/0.4 kV, 1 MVA power transformer. For both low and high voltage windings, we used 12 mm Amperium tapes from American Superconductor Co. For low-voltage winding 19 parallel tapes were wound on four mandrels and connected in series. High-voltage winding was wound with a single 12 mm tape. The assembled windings of each phase were tested at liquid nitrogen temperature without iron yoke. AC losses were measured in low-voltage winding at two modes: when high voltage winding was either shortened or open. In this paper, we present the details of current carrying element development and test, 1 MVA transformers winding designs and test results. [ABSTRACT FROM PUBLISHER]

The International Thermonuclear Experimental Reactor (ITER) has 60 high-temperature superconducting (HTS) current leads (CL) which have a nominal current of 68, 55 and 10 kA (depending on the type of magnet they have to supply) and provide a total current of 2.7 MA to the magnet system. The HTS module is a key part of CLs. This paper describes the simulation of the critical current in a multi-layer tape model as well as the special soldering technique developed for the HTS stack. In order to validate this technique, a 10 kA pre-prototype HTS module was made and tested in a setup that reproduces ITER conditions at ASIPP. The paper also briefly describes the overheating time test setup and the results. [ABSTRACT FROM PUBLISHER]

Current carrying capabilities of HTS tapes and coils can be defined by critical current when carrying DC current. While there is no standard criterion to judge their AC current carrying capability. In actual industrial applications, HTS tapes and coils often need to work in AC conditions. Accurately calculating the current carrying ability of tapes and coils is a precondition of designing a HTS machine. DC and AC V-I properties are measured using four-probe method under different background magnetic field. The method of measuring and obtaining the AC maximum working current is given. The applicability of the method and phenomenon of experiment is discussed based on the Anderson-Kim flux creep model. The content of this paper moderately contributes to the completion of superconducting technology. And the paper can be referenced when designing HTS machine with HTS tapes or coils carrying AC current. [ABSTRACT FROM PUBLISHER]

There are two kinds of high temperature superconducting motor (HTS) according to the angle of the superconductor's shape, one with the superconducting bulk and the other with the superconducting tapes. Using the superconducting tapes, HTS motors, whose superconducting magnets are located in the rotor, have been researched by many researchers and institutes. This paper research a novel HTS structure that the superconducting coils are placed in the slots of the stator made of ferromagnetic materials. This paper researches the magnetic field distribution of the superconducting coil in the slots and teeth of the stator. The electromagnetic field distribution under the influence of rotating magnetic field and ferromagnetic material is presented firstly. Then, considering the effect of coupling of AC current that flow in the superconducting coils, the distribution of magnetic field is further analyzed. Finally, in order to reduce the alternating current loss, a ferromagnetic slab is added beside the superconducting coils and the improved magnetic field distribution is researched. The simulation result shows that this method is instrumental in harvesting a decrease of the perpendicular flux density from the 0.34 T to 0.06 T. [ABSTRACT FROM AUTHOR]

This paper presents our new experimental facility and techniques to measure ac loss and current distribution between the layers for High Temperature Superconducting (HTS) cables. The facility is powered with a 45 kVA three-phase power supply which can provide three-phase currents up to 5 kA per phase via high current transformers. The system is suitable for measurements at any frequency between 20 and 500 Hz to better understand the ac loss mechanisms in HTS cables. In this paper, we will report techniques and results for ac loss measurements carried out on several HTS cables with and without an HTS shielding layer. For cables without a shielding layer, care must be taken to control the effect of the magnetic fields from return currents on loss measurements. The waveform of the axial magnetic field was also measured by a small pick-up coil placed inside a two-layer cable. The temporal current distribution between the layers can be calculated from the waveform of the axial field. [ABSTRACT FROM AUTHOR]

This paper presents the design and performance results of a pair of conduction-cooled brass current leads for a resistive superconducting fault current limiter (SFCL) system. The 24 kV class SFCL, which has been recently developed by the KEPRILSIS collaboration group in Korea, requires three pairs of conduction-cooled brass current leads operated continuously at 630 A. When the SFCL system is in the fault-mode, the current leads have experienced a 60-Hz fault current of ∼10 kA at 24 kV for 3–5 cycles. In this paper, we present the performance results of the conduction-cooled brass (commercial brass, 10% Zn) leads having a rated current of 667 A operated in a bath of liquid nitrogen. [ABSTRACT FROM AUTHOR]

This paper describes an effective method to calculate hysteresis loss of high-temperature superconducting (HTS) bulk material under time varying magnetic field. In the proposed method, the inner product of current and electric field in a HTS bulk is integrated to calculate hysteresis loss. To consider the nonlinear relation between the current and the electric field of HTS bulk material, critical state model and iteration method are adopted. According to the critical state model, if different types of time varying magnetic field are applied, the current distribution in a HTS bulk is affected not by applied field types but by peak-to-peak field values on the assumption of same critical current density regardless of different field types. This is the basic idea to compute hysteresis loss more effectively. This paper shows how to reduce total calculation time using the suggested method. To verify the validity of the suggested method, numerical results are compared with experimentally measured ones. [ABSTRACT FROM AUTHOR]

In this paper, we propose a new high-temperature superconducting (HTS) coil with shorter HTS tape length. In general, the critical current and n-value of an HTS tape depend on the applied magnetic field magnitudes and angles. Therefore, we derived fitting equations for the critical current and n-value in terms of these parameters obtained from the measurements of a Bi-2223/Ag tape at 77 K. Relatively large electric fields were generated at the coil edges because of the large magnetic fields and angles. This phenomenon prevents improvement of transport-current performance of an HTS coil. To solve this problem, we created a new HTS coil with edge vacancies and central separation. Analysis results revealed that the coil critical current increased significantly. Furthermore, we found an optimum coil shape that results in the improvement of the central magnetic field and stored energy by 33% and 99.5%, respectively, compared with those of the normal coil, irrespective of the reduction in the total HTS tape length owing to edge vacancies. [ABSTRACT FROM PUBLISHER]

In this paper, we derive integral equations for radially and polygonally arranged high-temperature superconductor thin tapes, and we solve them by finite-element method. The superconductor is modeled with a nonlinear power law, which allows the possibility of considering the dependence of the parameters on the magnetic field or the position. The ac losses are computed for a variety of geometrical configurations and for various values of the transport current. Differences with respect to existing analytical models, which are developed in the framework of the critical state model and only for certain values of the transport current, are pointed out. [ABSTRACT FROM PUBLISHER]

This paper presents the design of an AC loss experiment using nitrogen boil-off method. This experiment is aimed at exploring the AC loss of HTS double race-track coils which will be installed on the rotor of a wind turbine generator. The operating environment is simulated by designing a cryostat with rotating magnetic field windings. Apart from the fact that the alternating magnetic field causes most of AC loss on the HTS coils, we also believe that the DC background field would be another important factor causing AC loss if the HTS coil is experiencing by both alternating magnetic field in the perpendicular direction and DC background field in the parallel direction. In order to perform the boil-off measurement, we present the method to estimate the heat leakage in the cryostat which might cause errors to the measurement . [ABSTRACT FROM PUBLISHER]

This paper presents the optimization study of the field winding structure of the 20 MW-class HTS motor for the electric ship propulsion based on the minimization of the flux flow loss. The examples of the optimized shape of the HTS field pole coils obtained by the numerical analysis are presented. By optimizing the cross section of the field pole coil, it is found that the magnetic field perpendicular to the tape surface in the optimized shape coil significantly decreases compared with that in the rectangular shape base coil. As the results of the reduction of the perpendicular magnetic field, it is shown that the flux flow loss remarkably decreases. It is also pointed that the necessary length of the HTS tape for the optimized shape coil increases. [ABSTRACT FROM PUBLISHER]

In fabrication of a compact NMR (Nuclear Magnetic Resonance) magnet which consists of a stacked HTS (High Temperature Superconducting) bulk annuli, generally there are three key issues: spatial homogeneity, temporal stability, strength of trapped magnetic fields. This paper presents a study on the effects of axial gap length between stacked HTS bulks on the three key issues of a bulk HTS magnet for compact HTS NMR applications. The HTS bulk magnet of which the ID and OD are 20 and 60 mm respectively has a 50 and 80 mm heights depending on the axial gap lengths between HTS bulks. The gap length between each HTS bulk varied from 0 mm to 10 mm and were used as parameters to optimize, analytically as well as experimentally, the overall field homogeneity of the HTS bulk magnet. The optimized axial gap length was obtained by analytical results, and the better magnetic field homogeneity and temporal stability of trapped magnetic field were achieved by lower magnetization field. The improved spatial homogeneity and strength of generated magnetic field by a new compact NMR magnet will be presented. [ABSTRACT FROM PUBLISHER]

The electric device applications of a high temperature superconducting (HTS) bulk magnet, having stable levitation and suspension properties according to their strong flux pinning force, have been proposed and developed. We have been investigating a three-dimensional (3-D) superconducting actuator using HTS bulks to develop a non-contact transportation device which moves freely in space. In our previous work, the unstable movement characteristics of HTS bulk were observed under DC operation, and the AC control system was proposed in order to solve these problems. In this paper, the horizontal movement and the field decay characteristics as a function of the gap length between electromagnet and HTS bulk and the frequency of driving current were investigated experimentally. [ABSTRACT FROM PUBLISHER]

The knowing the critical current density JC is important to calculate AC losses in superconducting applications. Usually JC can be obtained from magnetization measurements or electric measurements based on global quantities as the magnetic flux or the voltage. In this paper a quick and direct magnetic method for determining JC is proposed. It is based on direct measurements of local magnetic field in the gap between two bulk HTS pellets. Field penetration measurements were carried out on HTS pellets at 77 K by applying increasing axial magnetic fields with a quasi constant sweep rate. This determination of JC is theoretically based on Bean model. JC is deduced from the complete penetration magnetic field BP. BP is deduced from the delay TP between the applied magnetic field Ba(t) and the magnetic field at the center between the two pellets B0(t). Numerical calculations allow deducing JC more precisely from theoretical calculations and measurements. The numerical calculations are made with the power law E=EC(J/JC)^{n}. For the determination of JC the influence of the gap due to Hall probe sensor and the applied magnetic field rise rate are taken into account. The influence of thermal is also studied. [ABSTRACT FROM PUBLISHER]

The paper reports on experimental and numerical studies of AC loss in a high temperature superconducting coil wound with a Bi2223/Ag tape. A measurement method of the AC loss in the HTS coil by using a power meter is proposed. The AC loss is measured on the test HTS coil made by stacking pancake coils wound with the Bi2223/Ag tape. The AC loss is also calculated using the numerical method developed in our previous work. The measured AC loss is compared with the calculated one. The agreement of measured and calculated data is reasonable and this shows the validity of the proposed measurement method. [ABSTRACT FROM PUBLISHER]

As a variation of the thermally actuated flux pump and the linear type magnetic flux pump (LTMFP), the circular type magnetic flux pump (CTMFP) device is proposed to magnetize a circular shape type-II superconducting thin film and bulk. The basic concept is the same as the thermally actuated flux pump: a circularly symmetric traveling magnetic field is generated below a circular shape superconductor to increase its trapping field. However, this traveling field is created by the three phase windings instead of heating gadolinium block. Apart from the LTMFP, the three phase windings are wound concentrically instead of linearly. The speed of the traveling field is controlled by the AC frequency and the magnitude of the field is controlled by the magnitudes of AC currents. In addition, a coil with DC current is wound around the three phase windings to provide a background field. The concept design is presented in this paper. The magnetic waveforms are analysed numerically by the COMSOL 3.5a software. The impedances of the three phase windings are calculated and a corresponding circuit design is presented. This rig can be used as an advanced tool to study the flux pump behavior of a circular shape superconductor. [ABSTRACT FROM PUBLISHER]