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The use of Rare-Earth BaCuO (REBCO) coated conductors is well adapted for Resistive type SFCL (Superconducting Fault Current Limiter) thanks to their high current carrying capability and high resistance per unit length. However, in case of fault currents in the range of the critical current Ic, the dissipation can be highly inhomogeneous along the length, leading to localized temperature elevations in the normal zones. This so-called hot-spot regime is well predicted by simulation tools but was seldom studied experimentally in a non-destructive way. This paper presents two experimental results highlighting the existence of the hot-spot regime. First, localized dissipation on a REBCO tape is observed through high speed recording of nitrogen bubbles synchronized with electric measurements. Second, the maximum temperature at the end of the limitation is studied as a function of the prospective current through measurements carried out on the conductor developed by the European Project FASTGRID. The maximum temperature is found experimentally to be highest for prospective current close to the conductor Ic. [ABSTRACT FROM AUTHOR]

DC HTS cable has attracted more and more attention in recent years due to its high efficiency in electric power grid and some locations with large current and short distance. If it is applied in the power transmission with current lower than 2 kA, the magnetic field at the position near the termination is usually neglected. Conventionally, most of the current lead is perpendicular to the cable conductor; the magnetic field generated by the current lead may affect the local critical current of the cable, particularly near the termination where the magnetic field is the superposition of the magnetic field created by the current lead and the cable conductor when the transport current is large. There are few papers calculating the influence of external magnetic field on the HTS cable by taking the current lead into account. This paper describes a method for calculating the influence of magnetic field created by the terminal currents on the critical current of the cable conductor. Based on the proposed method, two types of DC HTS cable by conventional design with large current capacity are analyzed, which confirms that terminal influence cannot be neglected when the cable carries large current. This method can also provide a useful reference when designing an HTS cable. [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]

Nowadays, a conductive cooling cryocooler for superconductor becomes used wildly. But in the absence of liquid helium, heat conduction becomes much difficult, which means conductive cryocooler conductors are more susceptible to disturbances than conductors immersed in liquid helium. A current-sharing temperature is a key design parameter for superconductors’ performance. In this paper, we analyze the issues of current-sharing temperature in the Nb3Sn/Cu conductor. Based on the power law model, we simulate and analyze the effects of power law index, magnetic field, and moderate intrinsic-strain on the current sharing temperature of Nb3Sn/Cu conductor operating in conductive cooling cryocooler, when the temperature of superconductor is aroused by disturbance. [ABSTRACT FROM AUTHOR]

The development of high-temperature superconductors (HTSs) brings us a new material to make high-field magnets. Some conceptual HTS composite conductors have been developed for large-scale magnets with high field, such as fusion magnets. In this paper, we propose three models of Bi2223 high-temperature superconducting composite conductors that may be applied to the China Fusion Engineering Test Reactor. We analyze the transport and magnetization loss of these high-temperature superconducting composite conductors during the charging process and in an alternating magnetic field by the finite element method, respectively. This provides simulated data for analyzing the stability of Bi2223 high-temperature superconducting composite conductors. [ABSTRACT FROM AUTHOR]

High-current superconducting links based on MgB2 superconductors are being developed at CERN for the feeding of the superconducting magnets of theLHCHigh-Luminosity project. TheMgB2 superconductors are very sensitive to the strain that unavoidably occurs during a cabling process. It is difficult to evaluate all the strains that can occur during cabling of MgB2 conductors, so the minimization of critical current degradation requires a step-by-step evaluation of current properties with the subsequent modification of some components of cable machines. This paper presents some practical results on cabling of MgB2 round wires and tapes in the nickel matrix from the Columbus Superconductor that are softer than other MgB2 wires. We compare the currents of the samples taken of the cables at different stages of the cabling with those at delivery, before, and after the modification of components of the cablingmachine. Temperature dependencies of critical currents measured in the range from 10 to 30 K are presented. [ABSTRACT FROM AUTHOR]

Institute of Electrical Engineering, Chinese Academy of Sciences has been focusing on high-field all-superconducting magnet project for many years. No-insulation (NI) winding technology, despite of its charging delay time, makes the magnet of much higher current density, and more important, self-protected. Based on the NI dry-winding technology, a 25 T/32mmbore superconducting magnet was designed as a combination of 15 T/160 mm bore low temperature superconductor magnet and a 10 T/32 mm bore high temperature superconductor insert. A prototype coil, composed of 15 double pancakes (DPs), was tested at 4.2 K. Test results show that the REBCO insert can generate a 9 T central field in a 15 T background field, and 11.2 T, self-field. While fully evaluation of this insert shows that bad splice joints and premature quenches occurred during the test. We have repaired the bad splice joint, replaced some broken DPs, and rebuilt some double-wound DPs to lower the current density at the top/bottom of the insert to improve the operation margin. After that, we will retest themagnet system. The latest design, construction, and test results of the 25 T all-superconducting magnet will be fully introduced in this paper. [ABSTRACT FROM AUTHOR]

The search for continuous improvement of the magnetic properties of coated conductors requires in-depth knowledge of vortex pinning. Microwave measurements of the superconductor complex resistivity are a very effective tool in obtaining complementary information on vortex pinning, in addition to conventional critical current density Jc measurements. The microwave characterization suffers, however, from geometrical effects when the superconducting films are not thick with respect to the penetration depth, as the high-frequency field leaks through the superconductor and also probes the underlying substrate structure. Whilst the resulting electromagnetic problem has largely been addressed in the case of insulating or semiconducting substrates, metal substrates in coated conductors require further consideration. In this paper, we address the issue of obtaining the microwave resistivity of thin superconducting films grown on metal substrates, with particular emphasis on the correct determination of the vortex parameters. We finally illustrate the extraction procedure on a real sample measurements performed on a YBCO film deposited on metal tape. [ABSTRACT FROM AUTHOR]

In this paper, we investigate whether by synthesizing superconductors that are tuned to a topological, nodereconstruction transition point, we could create superconducting wires that are intrinsically resilient to quenches. Recentwork shows that the exponent characterizing the temperature dependence of the specific heat of a nodal superconductor is lowered over a region of the phase diagram near topological transitions where nodal lines form or reconnect. Our idea is that the resulting enhancement of the low-temperature specific heat could have a potential application in the prevention of superconductor quenches. We perform numerical simulations of a simplified superconductor quench model. Results show that decreasing the specific heat exponent can prevent a quench from occurring and improve quench resilience, though in our simplemodel the effects are small. Further work will be necessary to establish the practical feasibility of this approach. [ABSTRACT FROM AUTHOR]

The goal of this paper is to study and analyze the effect of Sn concentration (14% or 16%), the mode of Ti-doping and the shape of Nb filaments on the thickness of the "parasitic" layers of prereacted Nb3Sn grains (formed before the diffusion annealing) in the ITER-type strands and strands for high field applications processed by bronze technology. The use of short (of total duration not more than 1 h) intermediate heat treatments at 500 °C does not allow avoiding the prereaction formation of Nb3 Sn in all the samples under study. Sn concentration in bronze decreases by 1.5-2.0% after heat treatments compared to the initial state in all samples. In the samples with Ti-doped bronze matrix and coupled Nb filaments, the average thickness of "parasitic" layers is 112 nm in the case of 14% Sn in bronze and 140 nm for a bronze matrix with 16% Sn. In the sample with 16% Sn in matrix and extended Nb filaments of intricate shape the average thickness of prereacted layers reaches 200 nm. It is concluded that to minimize the parasitic layers formation the strands with high tin bronze matrix should be subjected to short intermediate heat treatments at temperatures lower than 500 °C. [ABSTRACT FROM AUTHOR]

Transport properties of coated conductor tapes can be affected by stress and strain induced during fabrication, cooldown, and operation. Therefore, it is important to understand the strain/stress dependence of the critical current of the coated conductor tapes in the reversible region undermagnetic field considering practical applications such as magnets and coils. In this paper, the strain characteristics of critical current, Ic, inhigh temperature superconducting (HTS)-coated conductor tapes fabricated using reactive co-evaporation by deposition and reaction reinforced with brass-foil laminate were investigated under externalmagnetic field at various cryogenic temperatures while applying uniaxial tension. Results show that Ic dependences on magnetic field and temperature were similar between brass-laminated coated conductor and Cu-stabilized tape. The irreversible strain limit and the irreversible stress limit of brass-laminated coated conductor tape increased as temperature decreased from 77 to 20 K. This behavior resulted from thermal hardening of the coated conductor tape at low temperature. [ABSTRACT FROM AUTHOR]

In the application of high-temperature superconducting (HTS) tapes, they are prone to subject fatigue loadings such as repeated thermal cycles, periodic electromagnetic force, and so on, which will affect the performance of superconductors and lead to the degradation of superconducting magnets and power systems. To optimize the design of a superconducting device, it is important to fully understand the fatigue properties of REBCO conductors. Recently, fatigue loading that influences critical current (Ic) of HTS materials has been studied by several research teams. However, the influence of mechanical fatigue stress on REBCO tapes under background magnetic field has not been reported. In this paper, the Ic as a function of external magnetic field under different loading cycles was investigated at 77 K. The results showed that for fatigue damage of a YBCO-coated conductor, the influence of stress amplitude on Ic degradation is more significant than the maximum stress applied to the coated conductor. Under higher fatigue load cycles, the YBCO-coated conductor was insensitive to the external magnetic field. [ABSTRACT FROM AUTHOR]

Future high temperature superconductor (HTS) high field magnets using multitape HTS cables need 10-kA lowresistance connections. The connections are needed between the poles of the magnets and at the terminals in a wide-operating temperature range, from 1.9-85 K. The EuCARD-WP10 Future Magnets collaboration aims at testing HTS-based Roebel cables in an accelerator magnet. Usually, low temperature superconductor (LTS) cables are jointed inside a relatively short soldered block. Powering tests at CERN have highlighted excess heating of a joint following classical LTS joint design. The HTS Roebel cables are assembled from REBCO-coated conductor tapes in a transposed configuration. Due to this, the tapes surface the cable at an angle with the cable axis. A low-resistance joint requires a sufficiently large interface area for each tape. Within one twist pitch length, each tape is located at the surface of the cable over a relatively small non-constant area. This geometry prevents making a wellcontrolled joint in a compact length along the cable. This paper presents a compact joint configuration for the Roebel cable overcoming these practical challenges. A new joint called fin-block is designed. The joint resistance is estimated computationally. Finally, the test results as a function of current and temperature are presented. [ABSTRACT FROM AUTHOR]

ACloss of the superconducting conductor is one of the important factors for the application of the superconducting power devices since it determines the stability and operation cost. In this paper, based on introducing the structure of a quasi-isotropic hightemperature-superconducting (HTS) strand, we calculate ac loss of the quasi-isotropic HTS strand consisting of symmetrically stacked coated conductors using the Comsol Multiphysics software and present a calorimetric method for measuring ac loss of the HTS strand by optical fiber Bragg grating (FBG) in liquid nitrogen (LN2 ) temperature. Before the ac loss experiment, we calibrate the FBG in the temperature range of LN2, which illustrates the rationality of the FBG measurement at LN2 temperature. ac loss can be obtained by the calibration between energy loss of the HTS strand against wavelength of the FBG. The experimental results are in accord with the calculations, which indicates that methods of the numerical calculation and the measurement are feasible, they can be principally extended to the ac loss computation and experiment of other HTS conductors with complex structure. [ABSTRACT FROM AUTHOR]

The toroidal field system of the JT-60SA tokamak is composed of 18 NbTi superconducting coils. Each TF coil is composed of six cable-in-conduit conductor lengths, wound in doublepancakes, and carrying a nominal current of 25.7 kA. These coils are being tested in the single-coil configuration at the so-called cold test facility (CEA/IRFU, Saclay, France). The test program includes for all coils a quench test at nominal current obtained by a progressive increase of the operating temperature at helium inlet up to quench (around 7.5 K). Thanks to the accuracy of the voltage measurements, it has been possible to followthe very early development of the quench at the scale of a few millimeters normal length. The paper presents the evolution of the resistive voltages measured on eight coils before the safety discharge is triggered. In addition, this early quench development over one conductor length was also simulated using theTHEAcodewith relevant boundary conditions. Two different quenches, which occurred on two different coils, were analyzed, one starting on a central pancake (peak magnetic field) and the other starting on a side pancake (warmer conductor due to heat transfer from the casing). The simulations show good agreement with experiments, stressing particularly three phases in the quench development clearly identified in the measured resistive voltages of all coils. [ABSTRACT FROM AUTHOR]

In the framework of the European-Japanese project JT-60SA, the quench tests are performed for each of the 18 NbTi superconducting tokamak toroidal field coils (TFC) in the Cold Test Facility at the CEA Saclay, Gif-sur-Yvette, France. While launching these experimental quench tests, the conductor current sharing temperature (Tcs) is reached by progressively increasing the inlet helium temperature. The quite complex quench dynamics are then observed due to several coupled physical phenomena influencing the quench propagation. In order to better understand the experimental analyses on coils quench behavior, a numerical model has been used, combining the computation code thermal hydraulic and electric analysis of superconducting cables for the longitudinal quench transient modeling along the cable-in-conduit conductor, and an additional interturn thermal couplingmodel for transverse heat flux modeling. In this paper, several parametric studies will be done, thanks to simplified numerical simulations in order to identify the predominant physical phenomena driving the JT-60SA TFC quench propagation. The analysis focuses on the linear power impact on the quench initiation, the quench propagation dynamics, and the reverse flow effect. [ABSTRACT FROM AUTHOR]

Materials used as reinforcement for conductors in high-field magnets require both a high capacity for load bearing and a high resistance to deformation under stress; that is, a high value for tensile strength and a high modulus of elasticity. In addition, compatibility between the magnet conductor and any proposed reinforcement materials has to be carefully evaluated in terms of their capability for thermal expansion, stability at high temperature, resistance to oxidation, and crack propagation. We investigated a number of (nickel based and nickel-cobalt based) superalloys designed for high-temperature applications. These superalloys have higher Young's modulus than the stainless steels that are currently used as reinforcement materials for high-field magnets. Our test materials were subjected to thermo-mechanical processing that strengthens the alloys by forming very fine particles within them. Our initial work focused on changes that occured in the alloy during deformation at either cryogenic or room temperature. Because we observed distinct interfaces between the particles and the matrix, we decided that these materials could be described as precipitate-strengthened alloys. Both the strengthening component area and the matrix had more resistance to plastic deformation at cryogenic temperatures, than at room temperatures. In some cases, we further enhanced the strength of the alloy by doping them with other elements. In all the cases, these alloys permitted more efficient performance of conductors by shareing more of the load than would be possible with stainless steel reinforcement materials. This paper outlines the properties of these new alloys and establishes their compatibility with certain conductors commonly used for high-field magnets. [ABSTRACT FROM AUTHOR]

Quantum and radiological science and technology performed a toroidal field (TF) insert coil (TFIC) test in 2016-2017, which was newly developed in 2014 with the ITER TF conductor, in the central solenoid model coil test facility. According to the test program, the TFIC underwent more than 1000 cycles of energization to 68 kA under a 10.8 T background field, which represents the lifetime electromagnetic loads of ITER TF coils. Then, five cycles of warm-up to 290 K and cool-down to a temperature lower than 5 K were also performed. Through the test campaign, the transition of the current sharing temperature (Tcs ) was measured under the above energization condition. In parallel, two SULTAN test samples fabricated from the same TF conductor as the TFIC were tested by the similar test sequence to that of the TFIC, and the Tcs measurement results of the TFIC and the SULTAN samples were compared. In this paper, the test results mentioned above are reported. [ABSTRACT FROM AUTHOR]

In this paper, the transformer-type superconducting fault current limiters (SFCLs) with common connection point between two secondary windings, which was similar structure to the previously suggested transformer-type SFCL with two triggering levels, was proposed and their current limiting characteristics were compared. The suggested transformer-type SFCLs consist of the primary winding and two secondary windings with common connection point. However, the current limiting operations through two triggering levels, which can be generally adjusted by the winding direction and the number of turns between two secondary windings, are affected by the application position of two high-TC superconducting (HTSC) elements into the transformer type SFCL with common connection point. To analyze the dependence of the current limiting operation on the application position of two HTSC elements, the short-circuit tests for the transformer-type SFCL with two different positions of two HTSC elements were carried out and their current limiting characteristics were compared from the point of view of the power burden and the accumulated energy of two HTSC elements comprising each transformer-type SFCL. [ABSTRACT FROM AUTHOR]

We present design and test results for a thermallyactivated persistent-current switch (PCS) applied to a double pancake (DP) coil (151-mm ID, 172-mm OD), wound, using the no-insulation (NI) technique, from a 120-m-long, 76-μm-thick, 6-mm-wide REBCO tape. For the experiments reported in this paper, the NI DP assembly was immersed in a volume of solid nitrogen (SN2), cooled to a base temperature of 10Kby conduction to a two-stage cryocooler, and energized at up to 630 A. The DP assembly operated in quasi-persistent mode, with the conductor tails soldered together to form a close-out joint with resistance below 6 nΩ. The measurements confirm PCS activation at heating powers below our 1-W design target, and a field decay time constant in excess of 900 h (i.e., 0.1% h-1 field decay rate), limited by the finite resistance of the close-out joint. [ABSTRACT FROM AUTHOR]

Because the coefficient matrix is dense in the electromagnetic-field-analysis models of coated conductors using current vector potentials, the analyses of large-scale coils require a large amount of memory and long computation time. In this paper, we introduce hierarchical matrices by using the HACApK library in order to reduce both memory consumption and computation time. The effect of the method with respect to memory consumption and computation time is examined in numerical tests using a pancake coil wound with a coated conductor. The effect of parallel computations is also examined. Finally, we analyzed a large-scale magnet, with 1.5 million unknown values. [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]

The amplitude and rise time of fault currents can be reduced by installing a resistive-type superconducting fault current limiter (SFCL) in a voltage-source converter high-voltage DC (VSC-HVDC) system. Such an SFCL can provide sufficient time for a mechanical-type dc circuit breaker to interrupt a fault current. The objective of this paper is to elucidate the dc-current-limiting characteristics of Yttrium Barium Copper Oxygen (YBCO)-coated conductor tapes for a wide range of prospective currents (ranging from 50 to 10 kA). The factors investigated include critical currents (Ic) of the tape of 102 and 225 A, circuit time constants of 1 and 3 ms, and rated dc voltages of 250 and 500 V. The experimental results show that the limited current remains nearly constant with prospective current when the prospective current is higher than ten times Ic. The circuit time constant affects only the peak value and rise rate of the limited current. A single tape (I c = 102 A) can limit a 10-kA prospective current to a peak value of 555 A. The limited current for a rated voltage of 500 V is always higher than that for a rated voltage of 250 V. [ABSTRACT FROM PUBLISHER]

The CFETR, “China Fusion Engineering Test Reactor,” is a new tokamak device. Its magnet system includes the toroidal field (TF), central solenoid (CS), and poloidal field coils. The main goal of this study is to build a fusion engineering tokamak reactor with fusion power of 50–200 MW and self-sufficiency by blanket. The maximum field of CS and TF will get around 15 T, which is much higher than that of other reactors. New materials could be used to develop the magnet technology for the next generation of fusion reactors. Bi2Sr2CaCu2Ox is considered as a potential material for the superconducting magnets. An R&D activity is running at ASIPP for the feasibility demonstration of cable-in-conduit conductor based on the Bi2212 wire. One subsize conductor cabled with 42 wires was designed and manufactured. In this paper, the manufacturing procedures and first test results of Bi-2212 conductor samples are described in details, including wire specifications, cabling and compaction process, conductor heat treatment, as well as test results on ac loss and critical current. [ABSTRACT FROM PUBLISHER]

EuroCirCol is a conceptual design study for a post-LHC research infrastructure based on an energy-frontier 100 TeV circular hadron collider. In the frame of the high field accelerator magnet design work package of this study, three different layouts for double-aperture dipole magnets made of Nb3Sn conductors and providing a field of 16 T in a 50-mm aperture are being considered: block-coils, common-coils, and cosine-theta. All options are being explored and will be compared based on the same assumptions, in particular with regards to conductor performance, operating temperature and margin. This paper details the block-option presently under development at CEA. After an exploratory phase of various block-coils possibilities (cable dimensions, number of layers, cable grading) the design converged to a four layer magnet. An internal grading—two different geometries of cables are used in the coil—driven by a conductor saving is required. An electromagnetic analysis of the magnet cross-section in a 2-in-1 configuration is performed, coupled to a protection investigation. Preliminary results of a mechanical study on a bladder-and-key single aperture magnet are also reported. [ABSTRACT FROM PUBLISHER]

With the development of second generation (2G) high-temperature superconducting (HTS) tapes, several cabling configurations, such as twisting stacked-tapes cable and conductor on round core cables, have been proposed, and some prototypes were developed. Alternating current (ac) losses arise in HTS tapes in ac operations, and those losses are an important consideration for applications since they influence the stability and operating cost. Conventionally, a twisting technique is used to effectively reduce the ac losses. This paper presents the twisting properties and tensile properties of a quasi-isotropic (QI) strand made from 2G tapes. The strand consists of 2G tapes, aluminum foil, and a metal sheath. A twisting apparatus was designed and demonstrated to research the characteristics of the strands in twisting situations. The critical currents and strain of a single CC were tested for different twist pitches in self-field and at 77 K. The results show that the critical twist pitch of the QI strand is higher than that of a single tape. The critical current of the QI strand was also measured at 77 K after the application of different tensile stresses at room temperature. [ABSTRACT FROM AUTHOR]

Voltage tolerance during quench is one of the most important parameters for YBCO-coated conductors, especially for resistive type superconducting fault current limiter (SFCL) applications. How much voltage can be sustained per unit length of YBCO tape when experiencing fault current indicates the total required amount of the tapes to construct a resistive SFCL. In this paper, a step-down transformer is used to provide the short-current. As the voltage of the secondary side is not continuously variable, we change the voltage per unit length of the YBCO tape by varying the length of the tape. And the effect of the duration of short-current is also considered. A series of test have been performed to determine the maximum voltage drop that each YBCO tape can stand at fault current. The V-t curve has been measured after the tape experiencing successive quenches. Through a large number of experiments we will acquire the maximum endurable quenching voltage per unit length of YBCO tapes when experiencing short-current for different durations. The results presented in this paper would provide useful information for optimizing the design of a resistive SFCL. [ABSTRACT FROM PUBLISHER]

This paper presents magnetic-field distributions generated by screening currents flowing in short and straight multiple coated conductors exposed to a high magnetic field. The purpose of this study is to understand interactions between the magnetic field and the screening currents flowing in the coated conductors. In this paper, we suggest a method for calculating the magnetic-field distributions from current distributions. The method takes into account of the mutual screening current in the coated conductors. The magnetic-field distributions estimated using the method are in agreement with the experimental results. In addition, the current distributions inducing the magnetic-field distributions are described. [ABSTRACT FROM PUBLISHER]

In this paper, we focus on the quench detection and protection of a cryocooler-cooled pancake coil for SMES wound with a YBCO bundle conductor composed of laminated electrically insulated YBCO-coated conductors. Because the normal-zone propagation velocity is much slower in a high-temperature superconducting (HTS) coil than in a low-temperature superconducting (LTS) coil, the detection of the non-recovering normal zone using a voltage signal is quite difficult. Quench detection is considered to be more difficult during SMES operation because of the noise of the converter or other equipment. Therefore, a quench must be detected using some other method. In the previous paper, we showed that a quench in the coil could be detected by observing the transposition of the current in the bundle conductor caused by local normal transition. In this paper, based on this quench detection method, we investigate the transposition of current and the thermal behavior during the quench detection and the dumping of the stored energy by an external resistance in coils wound with a YBCO laminated bundle conductor for SMES and determine the appropriate stabilizer thickness of the YBCO-coated conductors. [ABSTRACT FROM PUBLISHER]

This paper describes two subjects, both aimed at the industrialization of Nb3Al conductors. One is the metastable solid-solution-strand restacking method, which is expected to be a low-cost Cu-stabilization method compared with the electroplating technique. In this paper, we mainly focus on recent efforts toward long-length production. The key point here is an improvement of the contact between the Cu tube and the restacked original strands. The second subject is the first attempt at “constant voltage” control in the continuous rapid-heating and quenching operation for 300-m-class precursor wire. With constant current control, changes in the diameter of the wire lead to variations in power per unit volume, so that the processing temperature changes. With constant voltage control, changes in diameter of the wire do not lead to changes in the power per unit volume, so that the processing temperature does not change and thus the uniformity of the longitudinal performance is improved. [ABSTRACT FROM AUTHOR]

Two of the three types of MICE magnets will have splices within their coils. The MICE coupling coils may have as many as fifteen one-meter long splices within them. Each of the MICE focusing coils may have a couple of 0.25-meter long conductor splices. Equations for the calculation of resistance of soldered lap splices of various types are presented. This paper presents resistance measurements of soldered lap splices of various lengths. Measured splice resistance is shown for one-meter long splices as a function of the fabrication method. Another important consideration is the strength of the splices. The measured breaking stress of splices of various lengths is presented in this paper. Tin-lead solders and tin-silver solders were used for the splices that were tested. From the data given in this report, the authors recommend that the use of lead free solders be avoided for low temperature coils. [ABSTRACT FROM AUTHOR]

This paper presents the models of three new-generation high-performance samples of ITER full-size Nb3Sn Cable-in-Conduit conductors (CICCs). These samples were recently tested in SULTAN, at CRPP (Switzerland), and demonstrated the technical feasibility of CICCs that satisfy the ITER specifications. The improvements of these samples regard not only the cable strand and the cabling parameters, but also the manufacturing details of their SULTAN samples. A set of changes have been adopted on the SULTAN sample termination and joint, to try to achieve a more uniform current distribution among the strands and a more accurate measurement of the strand longitudinal voltages. This paper presents a comparative numerical analysis of the effects that these different joint technologies have on the DC current distribution among the strands of the SULTAN samples cable. A correlation between the current distribution in the sample and the resistance distribution at the joint is also shown and discussed. [ABSTRACT FROM AUTHOR]

This paper presents the characteristic analysis on the high-Tc superconducting (HTS) electrodynamic suspension (EDS) simulator. In EDS maglev trains, the relative velocity between the moving high field magnet and the fixed ground conductor makes the magnetic reaction between two components. The magnetic reaction generates the levitation force of the EDS system. The distribution of the magnetic flux on the ground conductor affects the strength of the levitation force. A EDS simulator basically consists of levitation magnet and ground conductor and one of these component should be a moving part. In the static type EDS simulator, the levitation force is generated by the velocity equivalent AC current. Therefore, the static type EDS simulator does not need the high speed moving parts and can test the effect of the variations of the ground conductors easily by the change of the frequency of the applying AC current. To design the static type simulator optimally, the HTS levitation magnet and the characteristics of the EDS system were numerically analysed by 3-D finite element method (FEM). Based on the numerical analysis, the static type EDS simulator was designed manufactured and tested. The simulator consists of an HTS magnet, the fixed ground conductor(s), an AC power supply, resonating components, force measuring devices, and a supporting structure. From the calculation and test results on this paper, the consideration of the magnetic flux distribution according to the levitation height should be included in the process of the ground conductor design. [ABSTRACT FROM AUTHOR]

The paper refines the lumped network technique for computation the coupling AC losses and magnetically induced supercoupling currents in multistage cable-in-conduit conductors (CICC) used in superconducting magnetic energy storages, tokamak reactors, etc. Surfaces of the subcables in dcc are not "smooth", but "corrugated". As a result, the contacts between the subcables are featured with a certain periodicity, which depends on the pitches of the sequential cabling stages. The paper presents the expression for such a periodicity and the results of computation of AC loss and supercoupling currents with and without taking into account the envisaged periodicity of the contacts between subcables in multistage CICC, showing the significance of the effect. [ABSTRACT FROM AUTHOR]

The thermal stability and quench propagations are one of the most fundamental issues for the High Temperature Superconducting (HTS) coil. Superconductivity is confined within the phase surface bounded by magnetic field, temperature, and current. Of these three parameters, the temperature is neither completely controllable, nor predictable, because the energy stored in the magnet, can easily be converted into heat up setting the thermal equilibrium within the winding. Therefore, in HTS coil operation, the temperature stability or more generally the thermal behavior of the conductor is the most important. In this paper, a HTS double racetrack pancake coil was prepared to examine the thermal stability, quench propagation and minimum quench energy (MQE). HTS coil was wound using the AMSC Bi-2223. The experimental results are discussed in this paper. [ABSTRACT FROM AUTHOR]

To select electrical insulator (insulator) between coated conductor tapes (CC tapes) of two parallel non-inductively wound solenoid type superconducting fault current limiter (SFCL) is a important issue. Insulator is inserted for separation of two parallel tapes. Quench characteristics and recovery time of SFCL are related on insulator and thermal contact condition. Insertion of tape-shape insulating materials is a normal way of insulation for non-inductively wound SFCL. Thus, various tape-shape insulating materials can be the insulator of SFCL. In this paper, sample holder to simulate parallel tapes with various insulators was fabricated, and sticky polyimide tape and insulating paper tape were chosen for insulator of samples. Short-circuit test was performed in the same condition except inserted insulator of samples. Quench characteristic, generation of resistance, and recovery time of each sample were compared to the others. Special sample holder was used to observe current division and sharing in two parallel coated conductor tapes. The variation of the voltage applied to the module for short-circuit test was from 1.82 (V) to 12.7 (V). [ABSTRACT FROM AUTHOR]

HTS power cables appear to be the replacement and retrofitting of underground cable in urban areas and HTS power cable offers a number of technical and economic merits compared to normal conductor cable system. A 3 phase 22.9 kV, 50 MVA class HTS power cable system have been developed by Korea Electrotechnology Research Institute (KERI), LS Cable Ltd. and Korea Institute of Machinery and Materials (KIMM) that is one of 21st century frontier project in Korea. The 30 m long cable with 3 cores in 1 cryostat has been manufactured and installed to conduct long-term reliability test. The HTS power cable consists of two layers of phase conductor and two layers of shield used Ag/Bi-2223 tapes and polypropylene laminated paper is used in LN2 as electrical insulation. A HTS power cable has been tested with DC and rated current and voltage in pressurized liquid nitrogen. The evaluation results clarify good performance of HTS cable and these results prove that the HTS power cable has the basic electrical properties for 22.9 kV HTS power cable. This paper describes the results of developmental the 30 m, 3 phase, 22.9 kV, 50 MVA HTS power cable in Korea. [ABSTRACT FROM AUTHOR]

This paper presents the influence of current distribution on AC transport current loss in multi-strand high-temperature superconductor (HTS) tapes. The current-distribution-dependent-AC loss is analyzed by introducing a current distribution parameter. We calculated AC loss of multi-strand HTS tapes numerically and performed AC loss measurements as well. Though the effect of current distribution on AC transport current loss is relatively insignificant for a low applied transport current, the effect of nonuniform current distribution seriously increases AC loss for a high applied transport current. The AC loss measurement method used in this paper is also confirmed by comparison with numerical results: the experimental and computational results showed good agreement for various current distribution parameters. [ABSTRACT FROM AUTHOR]

In this paper, we studied electric insulation characteristics of synthetic Laminated Polypropylene Paper (LPP) in liquid nitrogen (LN2) for the application to high temperature superconducting (HTS) cable. And, we selected the insulation paper/LN2 composite insulation type for the electric insulation design of a HTS cable. Furthermore, we compared the breakdown characteristics of the butt gap and bent mini-model cable that comes into being in this kind of cryogenic insulation type. It is necessary to under- stand the winding parameter of insulation paper/LN2 composite insulation. [ABSTRACT FROM AUTHOR]

To obtain realistic data on HTS power cable, single-phase 30 m long, 22.9 kV class HTS power transmission cable system have been developed by Korea Electrotechnology Research Institute (KERI) and LG cable Ltd. that is one of 21st century frontier project in Korea. The HTS cable consists of Ag/Bi-2223 tapes, high voltage insulation paper which is impregnated by LN2. The cable is rated at 22.9 kV, 50 MVA, 60 Hz and is cooled with pressured liquid nitrogen at temperature from 70 to 80 K. This paper describes the results of design, fabrication and evaluation of the single-phase, 30 m HTS power cable system. [ABSTRACT FROM AUTHOR]

In this paper, a high-temperature superconducting composite right/left-handed (HTS CRLH) resonator is proposed, which is constructed by microstrip spiral coupled lines and step-like microstrip lines. The dispersion characteristics of the CRLH resonator is obtained and analyzed by an equivalent circuit model and a transmission matrix method. To verify this design methodology, the HTS CRLH resonator is designed and fabricated with a compact size of 11.25 mm $\times$ 16 mm on YBa2Cu3O7 films. The power handling capability of the filter is studied. Finally, the measured and simulated results are in good agreement with each other. [ABSTRACT FROM PUBLISHER]

Bulk materials of high-critical-temperature superconductors (HTSs) are promising for current leads and fault-current limiters because of negligibly small Joule heating under current transport and very low thermal conductivity. We consider that a Bi-2212 bulk superconductor prepared by the melt-casting process (MCP) is one of the best materials for these applications. In addition, MCP is well known to be a simple and economic process, and also served as a method for obtaining any sizes of HTS bulks consent to requirements for practical applications. In this paper, we present a study on the transport and quench properties of Bi-2212 bulk superconductors doped with \K2\CO3. First, the MCP samples doped with \K2\CO3 were analyzed by using an X-ray diffractometer and X-ray fluorescence spectrometry. In addition, the critical temperatures of the MCP samples doped with \K2\CO3 were observed. Then, we have investigated the relations between the critical current value and the doping quantity of \K2\CO3. The value of the direct-current critical current was determined at 77 K, and the self-fields derived from the electric field versus the transport current characteristics were obtained using a criterion of 1 \mu\V/cm. Finally, the alternating-current transport properties of the MCP sample were measured, and we have discussed the frequency dependence of the critical current with current distributions [ABSTRACT FROM PUBLISHER]

With much effort devoted by many research groups, the performance of 2nd generation (2G) superconducting wires, also called coated conductors (CC), was drastically improved, leading to many meaningful and impressive demonstrations of electric power devices. Now that the performances such as critical current, in-field characteristics, and mechanical strengths became sufficient to the application, the attention has moved to how we can produce long 2G wires with high uniformity. Many in-line inspection tools are tested and introduced to address these challenges. In this paper, we describe two methods that we adopted for in-line monitoring and feedback control of layer deposition. One is for texture control of ion beam assisted deposition (IBAD) of an MgO layer through reflection high-energy electron diffraction (RHEED) pattern monitoring and analysis. The other is for composition control of a superconducting layer through surface color observation and control of metal source evaporation rates. By applying the above two methods, we achieved in-plane texture of about 4.8^ \circ in the MgO layer, as measured by FWHM of phi-scan of (220) peak, and the critical current of 750 A/12 mm width in the GdBCO layer along the length of more than 650 m, with excellent uniformity. [ABSTRACT FROM PUBLISHER]

This paper proposed a hybrid power supply system for quasi-continuous high magnetic field systems at the Wuhan National High Magnetic Field Center. The hybrid power supply combines a battery power supply and a 12-pulse generator-rectifier power supply together. Based on the power supply, a 60 T dual-coil quasi-continuous magnet is presented. The inner coil and outer coil are powered by the battery power supply and the generator-rectifier power supply separately. Both coils are wound with soft copper wires reinforced by HS4-glass fiber. To verify the proposed design scheme, Matlab/Simulink and COMSOL Multiphysics 3.5a are adopted to build the simulation models of the hybrid power supply system and the 60 T dual-coil magnet. Simulation results show that the proposed system has enough margins to achieve a 60 T/100 ms quasi-continuous field. Higher fields can be achieved without large changes when advanced conductors and fibers are adopted. [ABSTRACT FROM PUBLISHER]

Manufacturing of superconducting \Nb3\Sn based Cable-in-Conduit Conductor (CICC) for Toroidal Field (TF) coils for the ITER tokamak under the responsibility of the ITER Domestic Agency for the Republic of Korea, ITER Korea, has been in progress since early 2012. Production of sufficient CICC needed to fabricate the first TF coil solely using Korean (KO) conductor has been achieved. Furthermore, low temperature performance verification tests near ITER operating conditions on a second CICC sample, following tests on a sample from the first KO CICC destined for an ITER TF coil, have recently been performed at the EPFL-CRPP SULTAN facility in Villigen, Switzerland. This paper provides an overview on all CICC that is destined for the first ITER TF coil to be fabricated with KO CICC, along with a brief summary of the results of the low temperature performance verification tests on KO CICC samples. [ABSTRACT FROM PUBLISHER]

A series of pancake coils using several kilometers of second generation (2G) (RE)BCO conductor has been fabricated as a part of a R&D program to build a large aperture high field solenoid for energy storage application. This paper discusses the preparation of double pancake coils and the test results at 77 K before assembling the final magnet. These tests played an important role in assuring: the quality of conductors, coil winding and assembly, and integrity of splices within the coils. [ABSTRACT FROM PUBLISHER]

In this paper, the high temperature superconductor (HTS) winding and multitoothed structure are newly incorporated into the doubly salient (DS) and flux-switching (FS) machines, leading to create two new magnetless machines, namely the HTS-based multitoothed switched reluctance (HTS-MSR) and HTS-based multitoothed flux-switching (HTS-MFS) machines. Consequently, the design equations of the three machines, namely the MSR, HTS-MSR, and HTS-MFS, are formulated. The corresponding performances are analyzed by using the time-stepping finite element method (TS-FEM). By utilizing both torque-producing zones, the two HTS-based machines can achieve better performances than the MSR one. Moreover, the HTS-MFS can offer higher torque density than the HTS-MSR, but associated with larger torque ripple. [ABSTRACT FROM PUBLISHER]

The ITER correction coils (CCs) are designed to be arranged toroidally around the machine inside the poloidal field coils and mounted on the toroidal field coils in order to compensate field errors arising from misalignment of the coils and winding deviations from the nominal shape as a result of fabrication tolerances, joints, leads, busbars CCs, and assembly tolerances. China is responsible for manufacturing all the CCs and their conductor. The paper presents the qualification progress and results of ITER CCs and CC conductor, including the test results of CC SULTAN samples, double pancakes winding experiments, CC case welding techniques, and manufacturing experiment of CC helium inlet/outlets. [ABSTRACT FROM PUBLISHER]

AC loss of \Nb3\Sn cable-in-conduit conductors (CICC) decreases after cyclic mechanical loading, but remains almost the same in case of Nb-Ti ones. It was observed during previous ITER CS, TF, and PF inserts tests in JAEA. The same phenomena have been detected on numerous ITER CS, TF, and PF short samples tested in the SULTAN facility. Experimental methods of ac loss investigation in JAEA-Naka and SULTAN were different, but the final results showed a good agreement. Analysis and numerical investigation of the present work were based on RF PF&TF CICCs SULTAN test results, theory of superconductivity, and our own physical and engineering understanding of evidence. Cyclic mechanical loading in both JAEA and SULTAN was initiated by electromagnetic force. In this paper, we attempt to explain why hysteresis, coupling, and mechanical loss decrease dramatically after cyclic mechanical loading and thermo-mechanical stress caused by WUCD (warm-up and cool-down) in \Nb3\Sn CICC. [ABSTRACT FROM PUBLISHER]

Various cabling methods for HTS flat tapes have been developed in the past few years. We have been developing a REBCO tape cabling method twisting a stack of tapes (TSTC). TSTC conductors were recently tested at high magnetic fields 4 T–20 T. The test results have shown some significant degradations during high current and high field tests. This paper investigates the mechanical characteristics of a TSTC conductor. Effects of transverse loads on single tapes and TSTC conductors were studied to evaluate and compare their mechanical behaviors. A device was designed to measure the critical currents of tapes and cables at 77 K as a function of transverse load. YBCO tapes from two different suppliers were examined. The mechanical transverse load was applied to TSTC conductors to simulate a load similar to the one caused by the natural electromagnetic load during operations. Taking into account the unique geometrical structure of a TSTC conductor, the effects of localized and uniform transverse loading conditions on a TSTC conductor were investigated. Several TSTC samples including single tapes and cables were tested. The experimental results are presented and discussed in the context of use of this type of conductor for high field magnets applications. [ABSTRACT FROM PUBLISHER]