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The High-Luminosity LHC Accelerator Upgrade Project (AUP) in the U.S. will construct quadrupole magnets to be delivered to CERN. An initial 3 tons, over 600 km total length of conductor was procured under the LHC Accelerator R&D Program (LARP) for this project. Programs for quality control(QC) at the supplier and quality verification (QV) at the laboratories were solidified into components of the overall quality plan for strand procurement under AUP. Measurements of the critical current (Ic) and residual resistance ratio (RRR), and related probes and techniques, are central to the quality plan. Described below is the verification testing that has taken place at the National High Magnetic Field Laboratory (NHMFL). Testing challenges are presented by the high sensitivity of these wires. In addition, new RRR test software was developed to accommodate challenges presented by meeting international standards with existing configurations of test strands., 4 pages, 7 figures

Large high field superconducting magnets often requires high current superconducting cables. In order to develop these cables, a facility capable of providing high magnetic field with large sampling area as well as electrical current of tens of kA is essential. A superconducting transformer is an energy-efficient and low-cost way to provide large current to superconducting cables. Previously, we co-developed a superconducting transformer and successfully tested it to a maximum output current of 45 kA in zero magnetic field. In this work, this superconducting transformer is installed to the 12 T split solenoid magnet at the National High Magnetic Field Laboratory (NHMFL). We calibrated it by using this facility to measure critical current of a NbTi Rutherford cable as a function of magnetic field up to 10 T, and compare the results with those available in the literature. In addition, a strand extracted from the NbTi cable is tested for critical current. The critical current of the extracted strand is scaled and compared with critical current of the cable. The accuracy of the critical current measurement using this superconducting transformer is discussed in detail. This work concludes the commissioning of this superconducting transformer which combined with the 12 T split magnet will provide unique cable testing capability for future cable development for the NHMFL and its users., Comment: 11 pages, 9 figures

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

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

The behaviour of solid-state batteries to many application-relevant operating conditions is intrinsically multiphysical and multiscale, involving the electrochemical performance and chemical stability coupled with the thermal and mechanical properties of multiple components. This review presents a holistic approach to discussing the multiscale physical-electro-chemical interactions and degradation mechanisms in solid-state batteries. While the propagation of lithium filaments depends strongly on the critical current densities, we show that effective prevention of excessive Li plating and stripping requires a combined understanding of solid-state electrochemistry, microstructure, mechanics, operating conditions, and their interactions. A review of how multiphysical interactions affect the optimum design of thin-film, three-dimensional and composite solid-state cell architectures is also included. Although the use of lithium metal as negative electrodes could improve the energy densities of solid-state batteries, we show that its high homologous temperature could cause cell failure during manufacturing. By comparing published model predictions with experimental observations, we present a critical analysis of the strengths and limitations of state-of-the-art models and characterisation techniques in solid-state battery research. This comprehensive mechanistic analysis provides an insight into the interplay among the multiple complex multiphysical mechanisms, shedding light on the process of cell design for next-generation solid-state batteries.

For the International Thermonuclear Experimental Reactor magnets, a significant fraction of the Nb3Sn conductors will be operating at a low field (B < 4 T), such as the outer turns of the central solenoid modules and toroidal field winding packs, while so far, the Ic(B,T, ) parameterization has been derived from measurements carried out at higher fields (B ≥ 7 T). It may not be accurate enough to adopt this parameterization for the extrapolation of the conductors' operating performance in terms of critical current (Ic) and current sharing (Tcs). The critical current characteristic can be effectively extended to the lower field region by means of a relation between the magnetization and critical current. The parameterization of the derived critical current scaling law Jc(B) is processed for the field range of the magnetization measurement (0 < B ≤ 9 T) and the critical current measurements (7 ≤ B < 12 T) in order to cover the full range up to 12 T.

Bi2Sr2Ca1Cu2O8+σ (Bi-2212) superconducting thin films were prepared using the sol–gel method on a LaAlO3 (LAO) single crystal substrate. The influences of oxygen content in the process of heat treatment on the orientation degree and superconducting performance of the Bi-2212 films are discussed, and the results show that changing the oxygen content in a mixed atmosphere during the high-temperature heat treatment process could control the growth orientation of the Bi-2212 films. When the oxygen content was in a range from 0.5 to 2.0%, with an increase in oxygen content, the c-axis growth orientation degree of the thin film presented a linear growth trend, but if the oxygen content was too high in the atmosphere, it could lead to the generation of impure phases. Further study found that both Tc and Jc of the film increased with an increase in the c-axis orientation degree. Among different oxygen contents, when the oxygen content in the atmosphere was 2.0%, the prepared sample had good biaxial texture, compact surface structure, and a regular atomic arrangement; the corresponding c-axis orientation degree could reach 97%, and the values of Tc and Jc were 85.3 K and 4.46 × 105 A/cm2, respectively.

An upgrading of the 25 T cryogen-free superconducting magnet (CSM) at the HFLSM to a 30T-class CSM is considered by replacing the present Bi2223 insert coil with a REBCO ones, since REBCO tapes have better mechanical and in-field critical current properties. In our strategy for the REBCO coil of the 30T-CSM, two tapes co-winding technique will be adopted in order to increase the space current density in the coil and to avoid a hotspot generation due to local degradation. Electromagnetic and mechanical properties of two bundle co-wound (two-ply) pancake coils are investigated as an R&D test coil for the 30T-CSM. The R&D coils were fabricated with Fujikura REBCO tapes that have 4.1 mm width and 0.11 or 0.15 mm thickness depending on the coil. The coil voltages and strains were measured at 4.2 K under a background field of 11 T. The maximum hoop stress up to 460–530 MPa at the outermost winding estimated by the BJR relation was applied, and no degradation by the hoop stress was found.

This study investigated the axial compressive stress dependence of the critical current of Rare Earth Barium-Copper-Oxide (REBCO) double-pancake coils. We measured the critical currents of REBCO coils cooled by liquid nitrogen while various axial compressive stresses from 0 MPa to 130 MPa were applied. After each stress was applied, the critical currents of the coils were also measured without the stress application to examine if the REBCO coils were irreversibly deteriorated. The experimental results showed that the REBCO coils were deteriorated at more than 100 MPa and the critical currents of the coils decreased by about 30% by applying 120 MPa to the coils. Moreover, reversible reduction of the critical currents of the coils were observed while the stresses of less than 100 MPa were applied. The reversible critical current decrease occurred even at a small stress, and the critical currents of the coils were reversibly reduced by about 15% while the stress of 100 MPa was applied. This study quantitatively clarified the dependence of the critical current of the REBCO coil on the axial compressive stress and the limitation of the axial compressive stress to prevent the deterioration of the REBCO coil.

The ability of HTS cable networks to provide a solution for the high power density requirements of electric transportation applications was explored. The high current density and the temperature-dependent critical current features of HTS cables were shown to allow resilient designs for power distribution in electric transportation applications. Heat loads at the terminations are shown to be the primary challenge. Appropriate designs in terms of ampacities of the current leads are essential in using the beneficial features of HTS cables. Thermal network models were used to understand the implications of using HTS cables to carry the necessary additional current to mitigate contingencies and to aid in the designs of effective HTS cable networks for electric aircraft and ships.

In order to improve the ability of superconducting transformer on limiting fault current, the parallel stainless steel & REBCO tapes are used as the winding materials. Firstly, the critical current of an individual REBCO tape and the parallel stainless steel & REBCO tapes under fault current are measured experimentally to compare their ability of limiting fault current. Then the current distribution in the parallel stainless steel & REBCO tapes under different fault currents are simulated. Lastly, a 6 kV/400 V (120kVA) HTS transformer is designed, and the fault current characteristics of wingdings are simulated based on finite element method (FEM). Experimental and simulation results show that the parallel stainless steel tape can improve the current limiting performance of the windings, which is of important referential value for the design of HTS transformer.

In this study, the trade-off among power consumptions, operating frequencies, and error rates in low-power single-flux-quantum (SFQ) circuit is investigated. The power consumption of SFQ circuits can be reduced by the lowering critical currents ( $I_{\mathrm{c}}$ values) of the Josephson junctions (JJs), or the bias voltage ( $V_{\mathrm{b}}$ ). The shifts and spreads of timing parameter fluctuations when $I_{\mathrm{c}}$ and $V_{\mathrm{b}}$ were lowered were numerically analyzed, with consideration of thermal noise at 4.2 K. The timing behaviors after $I_{\mathrm{c}}$ was lowered were relatively simple, being based on the signal-to-noise ratio, whereas those for lowered $V_{\mathrm{b}}$ values were complicated because of the dynamic behaviors of JJs driven at reduced voltage. The simulation results imply that the operating frequencies decreased because the timing windows narrowed, but the highest energy efficiency was obtained when we lowered $I_{\mathrm{c}}$ or $V_{\mathrm{b}}$ to 6.25% of their conventional values, and the energy reduction after lowering of $V_{\mathrm{b}}$ was 26% better than that after lowering of $I_{\mathrm{c}}$ . Moreover, if a small error rate (for example $10^{-6}$ ) is acceptable, further improvement in energy efficiency would be expected at significantly higher clock frequencies than would be the case if the SFQ circuit must exhibit error-free operation.

Since the initial identification of the iron-based superconductors (IBS) in 2008, numerous studies had focused on how to improve critical current density. However, the research of quench behaviors for iron-based multi-filamentary tapes was rarely reported. It is important to understand quench behaviors, and two main parameters should be examined carefully, i.e., normal zone propagation velocity (NZPV) and minimum quench energy (MQE). In this paper, a two-dimensional quench model integrating the stationary electrodynamics equations and heat conduction equation was proposed to study the quench propagation of iron-based Sr/Ba0.6K0.4Fe2As2 (Sr/Ba122) tape in different transport currents and temperatures. MQEs and NPZVs of IBS tape were calculated by the quench model, and the results were well complied with experimentally results which verified the correctness of the proposed quench model. In addition, since iron-based superconducting coils for high magnetic field application were operating in liquid helium mostly, an experiment was performed to study the quench behaviors of Ba122 tape in liquid helium, for the purpose of understanding the stability of the iron-based superconductor and designing quench protection systems of IBS coils reliably.

In this study, we introduce the concept of high-entropy into high-temperature superconductors and report the successful synthesis of a series of high-entropy oxides, REBa2Cu3O7-δ (REBCO), with superconducting critical temperature (Tc) around 92 K. The superconductivity transition temperatures of these compounds are very close to that of the parent superconductor, YBa2Cu3O7-δ (YBCO). The temperatures of the zero-resistance appearing (Tczero), the critical current density (Jc) calculated from the hysteresis loop, and the irreversible fields (Hirr) of REBCO are not improved compared to that of YBCO. Our results indicate that the introduction of high-entropy elements with strong magnetic moments at RE site does not affect Tc, but may decrease other superconducting properties such as Jc, Tczero, and Hirr.

The escape rate of S → R switching (from superconducting S state to resistive R state) in Josephson junction formed by s-wave single-band (SB) and three-band (ThB) superconductors (SB/ThB junctions) in macroscopic quantum tunneling regime is investigated. We use the effective critical current approximation in SB/ThB junctions. It was shown that escape rate can exhibit qualitative features in the case of frustration effects in ThB superconductors. Inclusion of Leggett modes in ThB superconductors leads to enhancement of escape rate in three-channel Josephson junction in comparison with single-channel junctions.

In this paper, based on the three-dimensional (3-D) H -formulation, we calculate the influence of local defects and non-uniformities on the AC loss in HTS round wires. By comparing intact round wires and round wires with local defects or non-uniformities, we found that when the peak value of the transport current is less than the critical current at the “bottleneck” of the defect, the difference between the two is small. When the peak value of the transport current is greater than the critical current at the “bottleneck” of the defect, the AC loss will increase significantly. The increase in the non-uniformities of the round wire makes the AC loss gradually increase. The increase in the pitch of the inhomogeneous distribution of the round wires will gradually reduce the AC loss.

Abstract The critical temperature of the surface superconductivity in vanadium (Tcs) is found to be 0.04 K higher than the critical temperature of its volume superconductivity (Tcv). Surface superconductivity persistent currents can effectively trap a magnetic flux. The critical current density of the surface superconductivity is estimated at js = 5 × 106 A/cm2 at T = Tcv.

YBa2Cu3O7−δ(YBCO)/Bi2Sr2CaCu2O8+δ(Bi-2212)/YBCO trilayer films with c-axis epitaxial orientation have been successfully prepared on LaAlO3 (LAO) monocrystalline substrates by sol–gel method using metallic acetates as starting materials. The effect of heat treatment temperature of upper YBCO films on the structure and superconductivity of YBCO/Bi-2212/YBCO planar-type junction have been studied. When the upper YBCO film fabricated at 750 °C, YBCO/Bi-2212/YBCO trilayer films exhibited good in-plane and out-of-plane growth texture and good superconductivity. Two superconducting transition steps in the R–T curves of YBCO/Bi-2212/YBCO trilayer films were clearly observed. Current–voltage (I–V) curves at 50–65 K of trilayer structure exhibit a supercurrent with zero voltage, and the superconducting critical current Ic is proportion to (1 − T⁄Tc)3.5. We suggest that a weak-link contact, which appears to have an SNSNS type structure, formed at the interface of YBCO/Bi-2212/YBCO trilayer structure.

Multifilamentary Bi2Sr2CaCu2Ox (Bi2212) composite wires are the only high-temperature superconducting round wires (RWs) with sufficient critical current density (Jc) for superconducting magnets generating magnetic fields greater than 25 T. Previous works indicated that various voids in Bi2212 filaments and bridges between the adjacent Bi2212 filaments in Bi2212 RWs were generated after heat treatment. Such complicated microstructural structure will inevitably affect its electrical behavior. Previous studies only focus on single microstructural feature, voids or bridges. Hence, we developed a numerical model containing both voids and bridges to explore the comprehensive influence of these two microstructural features. Due to the preliminary results, it shows that the E-J relationships of the models with bridges and with infinity bridges are similar in the case of numerous bridges between filaments. It indicated that we can build a simplified geometry structural model by removing all the bridges and bonding the adjacent filaments directly. And then the parametric study of the voids was carried out and the results explained that the height (diameter) of void is the key factor to dominant its electrical behavior.

Various strand concept for high-temperature superconductor (HTS) flat tapes have been developed in the past few years for fusion magnet applications. We developed a round HTS strand with soldered multilayer copper tapes as filler and support called SaMiT following the technic path of twisted stacked-tape cable. DC tests performed under bending and twisting condition demonstrated that the proposed design of the HTS strand is promising in the high current cable and magnet application, but the study on electromechanical properties against the transverse and cyclic load is still needed. A press device was designed to measure the critical current of SaMiT sample at 77 K and self-field as a function of transverse and cyclic load to simulate the electromagnetic force load during the magnet operation. Transverse load amplitudes have been applied up to 40 MPa and cyclic load up to 1000 cycles at certain load amplitude. The experimental results are presented and structural optimization suggestions are discussed with visual inspection and analysis.

The empirically reported values of the critical current density (jc) of Bi-2212 as 2.4 × 105 (jc1; Sample 1) and 1.0 × 106 A/cm2 (jc2; Sample 2) are intriguing because both of them correspond to the same values of the temperature T = 4.2 K and the applied magnetic field H = 12 × 104 G. This difference is conventionally attributed to such factors—not all of which are quantifiable—as the geometry, dimensions and the nature of dopants and the manners of preparation of the samples which cause their granular structures, grain boundaries, alignment of the grains and so on to differ. Based on the premise that the chemical potential μ subsumes most of these features, given herein is a novel explanation of the said results in terms of the values of μ of the two samples. This paper revisits the problem that was originally addressed in [Malik G.P., Varma V.S. (2020) WJCMP, 10, 53-70] in the more accurate framework of a subsequent paper [Malik G.P., Varma V.S. (2021) JSNM, 34, 1551-1561]. Besides, it distinguishes between the contributions of the electro-electron (e-e) and the hole-hole (h-h) pairs to jc—a feature to which no heed was paid earlier. The essence of our findings is that the jcs of the two samples differ because they are characterized by different values of the primary variables μi and , where is the effective mass of a charge-carrier and me is the free-electron mass and i = 1 and 2 denote Sample 1 and Sample 2, respectively. In the scenario of the charge-carriers being predominantly h-h pairs, the values of these parameters are estimated to be: μ1 ≈ 12.3 meV, η1 ≈ 0.58; μ2 ≈ 22.7 meV, η2 ≈ 0.94. Following from these and similar estimates when the charge-carriers are e-e pairs, given below for each sample are the detailed results for the values of the secondary variables viz. the number density of the charge-carriers and their critical velocity, the number of occupied Landau levels and the magnetic interaction parameter.

A 10 kA high-temperature superconductor current lead (HTS-CL) using a double-tube stainless steel (SS) shunt has been designed, fabricated, and tested at Institute of plasma physics, Chinese Academy of Sciences (ASIPP). The current lead consists of 80 parallel the second generation HTS coated conductor with critical current of 220 A at 77 K in self-field, a double-tube SS shunt, and Cu connectors. The 80 YBCO tapes are divided into 20 so-called panels, which are soldered into the 20 grooves on the surface of the double-tube SS shunt and Cu connectors, each panel contains four parallel YBCO tapes. A double-tube shunt consisting of two coaxial tubes is designed. A series of tests were performed to verify the feasibility of the HTS-CL. The measured joint resistance is about 0.3–0.4 μ Ω/cm2. The transport current of 10.515 kA was carried between 5 and 65 K for 1010 s with no quenching. The LOFA time of 569 s and the burnout time over 15 s meeting the design requirements.

The present study discovers the significant enhancement of critical current density by the pinning of borohydride and crystal defects in the hydrogen-treated MgB2 bulks. Based on the concept of gas doping, the nanosized borohydride Mg(BH4)2 is formed by synthesizing H-doped MgB2 bulks in an H2 atmosphere at 300 °C and 350 °C, and the critical current density was enhanced over the entire field. The H-doped MgB2 bulks are then experienced dehydrogenation at 300 °C and 350 °C, respectively, and the decomposition of Mg(BH4)2 induced nanosized pits on the surface of the MgB2 grains, leading to a further enhancement of critical current density, 1.5 × 104 A cm−2 at 20 K and 2.5 T, which is three times larger than that of the un-doped MgB2 sample, 4.8 × 103 A cm−2. The hydrogenation and dehydrogenation hardly changed the superconducting transition temperature or the pinning mechanism of the MgB2 samples. The enhancement of the critical current density is possibly attributed to the pinning effects of the crystal defects, and the reduction of MgO.

In this study, we have investigated the annealing effects on FeTe0.55Se0.45 single crystals in S and Te atmospheres. FeTe0.55Se0.45 single crystals were prepared by self-flux method. The as-grown sample shows a rather broad superconducting transition temperature around 6 K and low superconducting volume fraction, which is due to the relatively low proportion of superconducting phase. After being annealed in different vapor atmospheres, their superconducting properties, such as superconducting transition temperature, critical current density Jc, and superconducting volume fraction, could be greatly improved. All experimental results suggest that the bulk superconductivity of FeTe0.55Se0.45 single crystals can be obtained after annealing and thus present another option to remove the excess Fe, which paves the way for further practical application.

In this study, three different Y358 samples were produced by the melt-powder-melt-growth (MPMG) method at different maximum grain growth temperatures of 1030 °C, 1040 °C, and 1050 °C. The differential thermal analysis (DTA), X-ray powder diffraction (XRD), magnetic levitation force, trapped magnetic field values and magnetization measurements were performed. According to the results, the highest magnetic levitation force, the highest critical current density and the highest trapped magnetic field values were obtained from the sample produced at the temperature of 1050 °C.

We report achievement of non-Cu-matrix critical current density (Jc) in internally-oxidized Nb3Sn superconductors that surpasses the best state-of-the-art Nb3Sn and the Jc specification of the Future Circular Collider. We then explore the mechanism of the improvement, which was believed to be caused by refined grain size. However, our experiment showed that even with similar grain size, internally-oxidized wires had significantly higher Jc than non-oxidized wires. This, combined with transmission electron microscopy and atom probe tomography studies which showed a high density of intragranular nano-precipitates with suitable sizes as pinning centers in internally-oxidized wires, demonstrates a significant contribution from the nano-precipitates.

Here we present calculations of the critical current of dc SQUID based on Josephson junction with un-conventional current-phase relation. We analyzed two cases of current-phase relation of junction: with anhar-monic and Majorana term. It is shown that the changing of the critical current in the case of the small geo-metrical inductance of dc SQUID based on Josephson junctions with unconventional current-phase relation is determined by the amplitude of the second term in current-phase relation, the geometrical inductance of dc SQUID and external magnetic field. In the case of the high inductance of dc SQUID unconventional terms can be ignored.

When manufacturing YBCO structures using traditional methods, a certain compromise is usually reached, namely: films with the relevant morphology, but with low electrophysical parameters are used. In this paper, it is shown that YBCO bridges 4 μm in width with the perfect surface morphology, i.e., without defects, with the critical current density Jc ≥ 3 × 106 A/cm2 at temperature 77 K and critical temperature Tc ≥ 88 K can be obtained using the master mask method. The perfect morphology of the bridge surface, values of the critical current density and critical temperature are retained even after the repeated (additional) deposition of the YBCO layer onto the structure with the master mask. The results obtained from the experiments with fifteen samples suggest that, unlike electrophysical characteristics, the fixation of the standard (basic) parameters of the growth process is not sufficient to obtain the perfect morphology of the YBCO film surface.

The route that combines with the mechanically alloying (MA) and powder-in-tube (PIT) method is thought as a potential way to make cost-friendly Nb3Al superconducting wire, since the MA could produce the high-quality Nb(Al)ss supersaturated solid solution and thus obtain high-Jc Nb3Al superconductor. In order to know the effect of hot-pressure (HP) sintering on superconducting properties and flux pinning of Nb3Al, a series of Nb3Al superconducting bulks annealed at 950 °C for 3 h with different sintering pressure and ball milling time have been prepared in this work. The results suggest that for the mechanically alloyed Nb3Al superconductor, its critical current density (Jc) and superconducting transition temperature (Tc) can be significantly improved by HP sintering. Comparing with the atmosphere pressure (AP) sintering, the Tc, onset and Jc (8 K, 7 T) of HP Nb3Al sample with a milling time of 2 h increase from 15.1 K and 0.56 × 104 A/cm2 to 15.7 K and 6.03 × 104 A/cm2, respectively. Improvement of grain connectivity and flux pinning properties are thought to be mainly responsible to the enhancement of current-carrying ability of HP Nb3Al superconductor.

We study the influence of dysprosium (III) oxides on the superconductivity properties of Hg-1223 material. Dysprosium-free Hg-1223 and dysprosium-doped HgBa2Ca2Cu3DyxO8+δ (x = 0.00–0.075 wt%) superconductors are synthesized by sealed quartz tube technique. Our results demonstrate that a presence of dysprosium oxide not only makes the Ba2Ca2Cu3Oy multiphase precursor more reactive and enhances the kinetics of the reaction, but also leads to the promotion of the high-Tc phase and enhancement of the transport critical current densities Jc.

This article presents the impact of MgB2 wire bending and diameter on transport critical current density and irreversible magnetic field of a resultant coil. Unreacted MgB2 wires 500 mm in length and 0.63 or 0.83 mm in diameter have been used in the fabrication of small diameter (14 mm) superconducting coils. The coils were subsequently annealed under isostatic pressure of 1 GPa for 15 min at 700 °C and 725 °C. Our results indicate that larger wire diameter, higher annealing temperature, and bending lead to slight reduction of critical current density and irreversible magnetic field in the coil.

Superconducting cables or fault current limiters may encounter short-circuit currents during operation. When experiencing multiple overcurrent cycles, the critical current degradation of yttrium barium copper oxide (YBCO) tapes may occur. The performance degradation of YBCO tapes under overcurrent is a gradual process. It may take dozens or hundreds of overcurrent or overheating pulses. To get a better understanding of this process, we explored the performance change of YBCO tapes under repeated overcurrent. A life characteristics test platform was established. The electromagnetic performance degradation of YBCO tape under 50 Hz sinusoidal ac operating conditions was investigated, taking the effect of the overcurrent amplitude and duration into account. Meanwhile, the relationship between the number of overcurrent cycles and the I c degradation is proposed. The reason for this performance change is analyzed by comparing the 2-D current density distribution of the YBCO film before and after experiencing overcurrent. In addition, the U-I property and resistance variations of these tapes are presented. It is inferred that the cracking of the superconducting layer is the main cause of I c degradation. The experimental results provide meaningful references for the performance degradation of the YBCO tapes and related devices.

We present a Verilog-A based compact model for the superconductor-insulator-superconductor (SIS) Josephson junction. The model can generate both hysteretic and non-hysteretic current-voltage ( I-V ) response for the SIS junctions utilizing the Stewart-McCumber parameter. We calibrate our model with different SIS samples and demonstrate accurate matching between the simulated and experimental results. We implement temperature effect on the energy gap and the critical current of the superconductor to explore the dynamic trends in device characteristics. We calculate the junction inductance and energy as functions of junction current and temperature. We simulate the read/write operations of an SIS junction based cryogenic memory cell to illustrate the usability of our model.

Ferromagnetic Josepshon junctions (SFS JJs) are the basic cell of an intense research activity that extends to spintronics. The simultaneous presence of low-dissipative behavior and spin-filtering properties in JJs composed of ferro-insulating barriers (SIfS JJs) suggests their possible implementation in dissipationless versions of spintronics devices. Here, we establish a direct correlation between the suppression of the critical current in the experimental I–V curves of SIfS JJs and the spin-polarization factor derived in terms of the tunneling amplitudes for spin up and down carriers. A modelling of the JJs in terms of the Tunnel Junction Microscopic model allows to provide the scaling of the suppression parameter as a function of the barrier thickness.

The origin of the low magnetization anisotropy of the textured bulk samples consisting of highly anisotropic (Bi,Pb)2Sr2Ca2Cu3Ox (Bi-2223) high-temperature superconductor crystallites has been investigated. It has been established that the observed anisotropy is determined by the disordering of Bi-2223 crystallites in the sample. The measured anisotropy of the textured sample makes it possible to determine the magnetic angle characterizing the ordering of crystallites.

High-temperature superconductors (HTS) have great potential for magnetic levitation applications. Nowadays, coated conductor (CC) tapes are playing an increasingly important role in this field. Compared with HTS bulk materials, CC tapes have a higher critical current density and can be mass-produced, easy to shape, and have other important advantages for magnetic levitation applications. In order to gain an in-depth understanding of the relevant levitation characteristics of CC tapes, we studied the static magnetic levitation force between the permanent magnet and HTS tape stack, with the number of the CC tapes in the stack being 10 to 160. The experimental results show that the magnetic levitation force increases steadily as the thickness of the CC tape stack increases, but gradually reaches saturation.

In this paper, the crack-inclusion interaction considering the exponential distribution of critical current density is carried out for a functionally graded superconducting cylinder during the zero-field cooling (ZFC) process. By determining the stress intensity factors (SIFs) at the crack tips and performing magnetoelastic stress analysis, the result indicates that the increase of the gradient parameter of critical current density could effectively reduce the stress intensity factors based on the effect of the gradient parameter on the elastic constants ratio of inclusion/matrix, sizes of the inclusion and crack, and the distance between them upon electromagnetic force.

We report the design for a hybrid block-coil dual dipole using advanced cable-in-conduit windings. The dipole is designed for use in the arcs of an energy-doubling lattice in the LHC tunnel. The block-coil design facilitates configuration of hybrid sub-windings of Bi-2212 and Nb 3 Sn, each operating to the same fraction of critical current. The cryogenics utilizes supercritical helium, operating in the window 4.3-5.5 K. A novel support structure provides robust support and stress management. The three sub-windings can be separately wound and heat-treated, then assembled and preloaded to complete the dipole. The short-sample field using commercially available Nb3Sn and Bi-2212 is 16.8 T. With a recently reported APC Nb3Sn, the short-sample field is 18.5 T.

30-core MgB2 superconducting wire with a diameter of 1.0 mm has been prepared by the conventional in-situ powder-in-tube (PIT) method. The metallographic analysis results show that the 30-core MgB2 wire has good uniformity in both transverse and longitudinal directions, and the critical current ( I c) and critical current density ( J c) at 4.2 K and 4 T reach 82.6 A and 7.3 × 104 A/cm2, respectively. Furthermore, (6 + 1)-structure MgB2 superconducting cables have also been successfully fabricated with different twist pitches ( T p) by the twisted and reacted (T&R) route, comprising six 30-core MgB2 wires around one copper wire in the center. The I c of the (6 + 1)-structure MgB2 superconducting cable with 50 mm T p reaches 467 A at 4.2 K and 4 T, suggesting no degradation of the MgB2 wire when self-field effects are taken into account.

The performance degradation of superconducting equipment under repeat fault is a key issue for the operation of superconducting equipment in grid operation. The mechanism of the High Temperature Superconducting (HTS) tape performance degradation behavior is an important issue that need to be figured out. Therefore, it's necessary to carry out the performance degradation study of HTS tape under repeat overcurrent. In this paper, considering overcurrent duration, a series of repeated overcurrent experiments were carried on YBCO tapes under 50 Hz sinusoidal alternating current. The degradation of critical current of YBCO tapes after repeat overcurrent was recorded. The critical current density of the YBCO tape was scanned to track sample's structural change during experiment. The mechanism of the degradation development of YBCO tapes after their first degradation was described. The research could provide a reference for the design of fault protection and life assessment of HTS devices.

In practical applications, the critical current of high temperature superconducting (HTS) tapes is usually influenced by different magnetic field magnitudes and different relative magnetic field orientations. In order to design HTS power devices accurately, it is vital to study the critical current behavior of HTS tapes under different magnetic field. In this work, a series of experiments have been performed to study the critical current characteristics of seven types of commercial HTS tapes from Sumitomo, AMSC, SuperPower and SuNAM at 77 K, low-strength and 0–90° magnetic field. The experimental results and analysis have been introduced in details, including the field angle dependence of critical current of the HTS tapes. The normalized critical current ranking and anisotropy index of seven types of commercial HTS tapes are given. Furthermore, a method for estimating critical current at some magnetic field angles based on the maximum and minimum critical current values of the HTS tapes is proposed.