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We investigated the effect of 0.6 MeV proton irradiation on the superconducting and normal-state properties of thin-film YBa 2 Cu 3 O 7 − δ superconductors. A thin-film YBCO superconductor (≈567 nm thick) was subject to a series of proton irradiations with a total fluence of 7.6 × 10 16   p / cm 2 . Upon irradiation, T c was drastically decreased from 89.3 K towards zero with a corresponding increase in the normal-state resistivity above T c . This increase in resistivity, which indicates an increase in defects inside the thin-film sample, can be converted to the dimensionless scattering rate. We found that the relation between T c and the dimensionless scattering rate obtained during proton irradiation approximates the generalized d-wave Abrikosov–Gor'kov theory better than the previous results obtained from electron irradiations. This is an unexpected result, since the electron irradiation is known to be most effective to suppress superconductivity over other heavier ion irradiations such as proton irradiation. In comparison with the previous irradiation studies, we found that the result can be explained by two facts. First, the dominant defects created by 0.6 MeV protons can be point-like when the implantation depth is much longer than the sample thickness. Second, the presence of defects on all element sites is important to effectively suppress T c . [ABSTRACT FROM AUTHOR]

Medium‐speed wind generators in the MW‐range with high‐temperature superconducting excitation winding are analyzed by means of non‐linear 2D and 3D FEM models. Besides an inverter‐based sinusoidal stator current feeding, a grid connection via a diode rectifier is analyzed by using coupled FEM and circuit simulations. The newly proposed modeling techniques are used to determine the excitation requirement for speed‐variable, unity power factor operation at constant stator voltage, as required for a diode rectifier feeding of the stator winding. 2D FEM models in the H‐A‐formulation are developed and used for the calculation of the hysteresis loss in the superconducting field winding at stationary operation as well as for an investigation of field current variations in the HTS field winding. The major modeling challenges consist in very long settling times of voltage‐fed models, several strong model non‐linearities and high requirements on the spatial discretization. Approaches for overcoming these difficulties with reasonable computational efficiency are proposed. [ABSTRACT FROM AUTHOR]

In this paper, we analyze in detail the features of the application of the magneto-optical imaging technique for studying HTS tapes. We present a detailed description of the experimental technique and features of the research facility for low temperatures research. The features of the penetration of a magnetic field into a superconductor are described, and the procedure for calibrating a magneto-optical film and algorithms for calculating magnetic field profiles from magneto-optical images are described in detail. [ABSTRACT FROM AUTHOR]

A superconducting magnet system is developed for the application of high-frequency gyrotrons at Wuhan National High Magnetic Field Center, China. The operating cost for the magnet is dominated by refrigeration power. To reduce the heat load for cryogenic systems, a pair of YBCO binary current leads is designed by consideration of the industrial concentration of type II high-temperature superconducting YBCO material. In this paper, a simulation model is proposed to perform the electromagnetic-thermal coupling analysis of these YBCO binary leads under different operating conditions by combining a partial element equivalent circuit method and finite volume method. The simulation code can improve computational efficiency and enable high-accuracy coupling between the electromagnetic field and heat transfer process. In the steady state, the heat leakage at the 4.2 K cold end of the YBCO binary leads depends mainly on the geometric parameters of the YBCO tape, especially the cross-sectional area of the copper layer in the YBCO tape. The cooling mode and liquid helium level also have a significant impact on the heat leakage level. The optimal outer diameter of the normal copper section is identified, and the optimum value is largely influenced by the effective cooling power imposed on the cold end of the normal copper section. In the transient state, simulations for the charging process and the loss of cooling accident are performed, along with a detailed analysis of the electromagnetic-thermal response features of the leads under these conditions. The results indicate that the YBCO binary current leads possess high thermal stability and an ample time margin for the magnet system to be demagnetized. [ABSTRACT FROM AUTHOR]

High-temperature superconductors are anisotropic materials and are often subjected to variable external magnetic and temperature fields. The non-uniformity of excitation environment and material will lead to the increase of AC loss and change of magnetostriction effect of superconducting material, which will result in unstable operation and even fracture damage of the equipment. In this paper, cylindrical high-temperature superconductors with material anisotropy are placed in a periodic alternating magnetic field. By controlling the amplitude of external magnetic field, excitation frequency, and non-uniform coefficient of material elastic modulus and ambient temperature, the distribution of electromagnetic field, temperature field, and magnetization intensity during the magnetization of superconductors has been investigated in depth. The AC loss and magnetostriction with the external field loading and unloading process are also discussed in detail based on the electro-magnetic-thermal coupling effect. The results demonstrate that variations in the amplitude and excitation frequency of the external magnetic field will have a remarkable effect on the trapped field, AC loss, and magnetostriction of the superconductor. The change in the non-uniformity coefficient of the material's elastic modulus only has a greater effect on magnetostriction, but has no significant changes on the trapped field, magnetic moment distribution, and AC loss. [ABSTRACT FROM AUTHOR]

An approach to numerical simulation of three-dimensional electrical and thermal fields in high-temperature superconductors is described. In such a semiconductor, the phenomena of superconductivity are observed at high temperatures above the temperature of liquid nitrogen. The absence of a generally accepted theory of superconductivity leads to the need to study physical processes in semiconductor structures using mathematical simulations. The main attention is paid to the calculation of temperature and electric current distributions in large-size mesas with a self-heating effect. An efficient algorithm for solving the equations describing these distributions is constructed. The basis of the algorithm is an adaptive multigrid method on structured Cartesian grids. The adaptability is based on the Chebyshev iterative method for constructing the smoothing procedures at each grid level and for solving the coarsest grid equations. The adaptive technique allows us to realistically simulate the anisotropic phenomena. The functionality of the algorithm is demonstrated along with an example of solving an anisotropic model problem with discontinuous coefficients. [ABSTRACT FROM AUTHOR]

Herein, a novel method of photoresist-free micropatterning, i.e., self-sensitive chemical modification (SSCM) photolithography , is developed to prepare micron-sized superconductor fine-pattern arrays and cross-shaped GdBa 2 Cu 3 O 7-x /YBa 2 Cu 3 O 7-ẟ heterojunctions. The X-ray diffraction and R-T analysis revealed that the SSCM photolithography did not influence the structural and superconducting electronic properties of the GdBa 2 Cu 3 O 7-x /YBa 2 Cu 3 O 7-ẟ heterojunctions. Therefore, the proposed method is well suitable for the microfabrication of multilayer superconductor films and is expected to widen the application horizon of high-quality superconductor junction arrays. Furthermore, the electrical test results of cross-shaped structure demonstrated that the I–V curves of GdBa 2 Cu 3 O 7-x /YBa 2 Cu 3 O 7-ẟ heterojunctions are similar to that of DC Josephson effect. The transmission electron microscopy revealed the presence of an intermediate transition layer (~1.2 nm) at the GdBa 2 Cu 3 O 7-x /YBa 2 Cu 3 O 7-ẟ interface, which may hamper the transmission of Cooper pairs. These results provide novel insights into the preparation of Josephson junctions and other junction devices. [ABSTRACT FROM AUTHOR]

Copyright of Metallophysics & Advanced Technologies / Metallofizika i Novejsie Tehnologii is the property of G.V. Kurdyumov Institute for Metal Physics, N.A.S.U and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

The microstructure of a bulk superconductor may fundamentally affect its field trapping and levitation performance for practical applications. Recently, a modified top-seeded melt growth using only Y2O3 and Ba2Cu3Ox precursor powder combined with a layered arrangement of graded Y2O3 content was reported to significantly refine Y2BaCuO5 particles as well as their distribution. In this paper, we have evaluated and compared the trapped field of a CPP (conventional precursor powder), an MPP (modified precursor powder), and an L-MPP (layered and compositionally graded) sample magnetized by both field cooling magnetization (FCM) and pulsed field magnetization (PFM) at 77 K. The 25 mm diameter YBa2Cu3O7-δ sample made from L-MPP shows the highest trapped field of remarkably 1.01 T and an advanced in-field performance. And the trapped fields achieved via PFM are close to (>93%) that obtained by FCM for all the three samples. However, a more dramatic flux motion has been observed for the MPP and L-MPP sample during the PFM process. The resulted trapped field distribution exhibited the effect of the homogeneity of the sample on the trapped field. [ABSTRACT FROM AUTHOR]

In this paper, fracture behavior of a micro-scale double cantilever beam (DCB) made of superconducting materials is investigated based on the strain gradient theory. Both zero-field cooling (ZFC) and field cooling (FC) magnetization processes are considered. The closed-form solutions of the energy release rates and stress intensity factors are obtained. For ZFC process, superconducting materials are easy to damage during the process of reducing magnetic field rather than increasing magnetic field. For FC process, applied magnetic field will impede superconductors to damage. Moreover, the normalized energy release rate predicted by classical beam theory is larger than that predicted by strain gradient theory. As the characteristic length increases, the normalized energy release rate decreases. The present model may be useful for designing experiments to test the fracture toughness of micro-scale high-temperature superconductors. [ABSTRACT FROM AUTHOR]

An alternative technique for synthesizing high-temperature superconductor samples is proposed, in which superconducting layers should form on the surface of hard-melting Ho2BaCuO5 green phase grains immersed in the liquid phase BaCuO2 + CuO. [ABSTRACT FROM AUTHOR]

A superconducting flux-pinned docking interface (FPDI) offers an important approach to spacecraft assembly, reconfiguration, and short-range formation flying. Although the self-capture ability was primarily presented, the flux-pinned interaction usually shows poor damping behavior, which does not benefit the vibration suppression of the superconducting interface structure subject to external excitation. In this paper, four superconductor structures including composite superconductor structures are proposed to analyze the dynamic process and self-stability of FPDI module. The effect of composite superconductor structures on the docking performance of the module under different field cooling (FC) conditions was investigated. After the FPDI module was in formation, an identical external disturbance was applied to the module to investigate its self-stability under the same FC magnetization condition. Calculating and comparing the damping ratio in different superconductor structures, we found that the FPDI module composed of the composite superconductor structure shows more extraordinary damping properties and self-stability characteristic than that using the conventional superconductor structure. [ABSTRACT FROM AUTHOR]

This research carried out experiments on the superconducting compound HgBa2Can−1CunO2n+2+δ at n = 2, 3. The samples were prepared using a sealed quartz tube. XRD analyses were used to determine the crystal structure and their parameters for both Hg-1212 and Hg-1223. Many software packages were used to refine and simulate the crystal structures. It was clear that the final phase in all cases was a tetragonal phase with a space group symmetry P4/mmm (123), and shrinkage along the c-axis of about 0.2 from the theoretical value. There was a slight variation in the basal plane axis and a sharp increase in the c-axis as a function of n. The presence of an octahedron structure within the unit cell is the origin of the charge reservoir, and increasing the number of octahedrons per unit cell is the reason to increase the concentration of the electronic charges per unit cell. Iodometric titration was done to show the excessive oxygen content, during the creating of tetrahedron structures. The last reason is to determine the amount of oxygen insertion within the structure. Resistivity measurement was necessary in order to determine the critical temperatures and related resistivity, creating the correlation with Miller indices and lattice constants. At the same time, the tetrahedrons are the main topics in developing the conductivity. It was clear from the electrical resistivity that the critical temperatures were 115 and 125 K for Hg-1212 and Hg-1223, respectively. These critical temperatures were in agreement with the data from the vibrating sample magnetometer (VSM). There were magnetic susceptibilities in both phases, i.e., χ = − 0.25 × 10−2 and − 0.41 × 10−2 for the Hg-1212 and Hg-1223 phases, respectively. It was concluded that many parameters were related to the conductivity and magnetic susceptibility of both phases. The induced magnetic field is 99.75% for n = 2, and 99.59% for n = 3. This result is in agreement with the results of penetration depth for both systems that showed greater value for n = 3 than for n = 2. [ABSTRACT FROM AUTHOR]

With the expansion of distributed power systems and renewable energy worldwide, the use of synchronous condensers (SC) has been gradually increasing to maintain the power quality of an electric grid. Because SC generates fewer harmonics and has the advantage of strengthening system inertia, it is considered as a primary option in Korea over other options such as Static Var Compensator (SVC) and STATic synchronous COMpensator (STATCOM). If superconductor synchronous condenser (SSC) is applied instead of SC, it brings more advantages: (1) it can minimize the adverse impact on the power system due to lower synchronous reactance, and (2) the higher power density can lead to many advantages in a limited area of substation. With these backgrounds, we report a design study on 40 MVAr SSC with no-insulation high-temperature superconductor (NI-HTS) field coil. Firstly, design criteria and procedures for electromagnetic design were set. Secondly, with the design procedure, the electromagnetic design having the minimum HTS conductor usage was obtained among the designs satisfying design criteria. Based on the final design, key characteristics of SSC including no-load voltage, the maximum flux density under the rated-load condition, V-curve characteristic, synchronous reactance, zero sequence reactance, negative sequence reactance, critical current, and NI-HTS characteristics were calculated by using finite element method. Lastly, the design comparison between SSC and SC was presented. • The use of synchronous condensers has been gradually increasing. • Superconductor synchronous condenser is a promising alternative option. • It has not only a much lower synchronous reactance but also a higher power density. • The advantages were confirmed through the electromagnetic design study. [ABSTRACT FROM AUTHOR]

We present a perspective on a new critical-current-by-design paradigm to tailor and enhance the current-carrying capacity of applied superconductors. Critical-current-by-design is based on large-scale simulations of vortex matter pinning in high-temperature superconductors and has qualitative and quantitative predictive powers to elucidate vortex dynamics under realistic conditions and to propose vortex pinning defects that could enhance the critical current, particularly at high magnetic fields. The simulations are validated with controlled experiments and demonstrate a powerful tool for designing high-performance superconductors for targeted applications. [ABSTRACT FROM AUTHOR]

The expressions for the renormalized phonon group velocity (RPGV) has been developed from renormalized phonon dispersion relations obtained with the help of impurity-induced anharmonic quantum dynamics of phonons via Green's functions. It is observed that RPGV shows dependence on doping, phonon frequency, temperature, and anharmonicity. The La 2 − x Sr x CuO 4 superconductor has been taken for model calculations to successfully apply the new results of RPGV. [ABSTRACT FROM AUTHOR]

• The flux, generated by a DEMO CS coil of fixed outer radius, is maximized. • Use of high- T c superconductors would allow a 32% increase of the generated flux. • Layer-wound CS coil design with superconductor and steel grading is proposed. • In the highest field sections, the use of high- T c superconductors is envisaged. The present work is performed within the framework of the EUROfusion DEMO project. Previously, it was demonstrated that for a maintained magnetic flux the use of HTS conductors at highest magnetic field in a layer-wound CS coil would allow the reduction of its outer radius by around 0.5 m as compared to the DEMO reference design using only Nb 3 Sn conductors. Alternatively, the superior high field performance of HTS conductors can be used to maximize the magnetic flux of a CS coil with a given outer diameter, which could significantly prolong the duration of plasma burn phase and thus the overall power plant efficiency. In the present study, the maximization of the magnetic flux, generated by a layer-wound CS coil of fixed outer radius, is considered. HTS conductors are envisaged to be used at highest field, while Nb 3 Sn and NbTi are foreseen to be used in intermediate and low field layers, respectively. The inner radius of the CS coil is optimized with respect to the generation of a maximum flux taking into consideration the superconductor properties, the hoop stress and the axial stress. In order to provide reasonable starting values for the finite element analysis, first a simplified model with layer-dependent current densities, however, without stainless steel grading will be considered. In the final outline design of the CS coil a superconductor and stainless steel grading will be implemented. [ABSTRACT FROM AUTHOR]

We study here a single band Hamiltonian model to describe the effect of next-nearest-neighbor (NNN) electron hopping on superconducting gap in Cuprates. The Hamiltonian consists of nearest-neighbor (NN) and next-nearest-neighbor (NNN) electron hopping integrals between the copper sides. By taking d-wave pairing symmetry into account, BCS type superconducting interaction is studied. By applying Zubarev's Green function technique, the total Hamiltonian is solved. From the correlation function, the temperature-dependent superconducting gap (SC) equation is derived and is computed self-consistently by using technique 1 0 0 × 1 0 0 grid points of the electron momentum. By varying SC coupling, chemical potential, J-T coupling parameter and second-nearest-neighbor electron hopping integral, the evolution of the order parameter is investigated. [ABSTRACT FROM AUTHOR]

Influence of γ-irradiation on the optical properties of a polyimide film and its polymer compositions with fillers of a dispersed powder of a high-temperature superconductor ҮBa2Cu3O6.7 (YBaCuO) with concentrations of 0.05, 0.10, and 0.50 wt.% was studied. It was established that γ-irradiation with a dose up to 600 kGy does not affect the transparency of polyimide films in the visible region of the spectrum. However, at irradiation doses of 250 and 600 kGy, a weakly expressed fine structure appears in the spectra of polyimide films in the range of 220-300 nm due to the contribution of the resulting diene structures to the optical transmission and the increased content of oxygen atoms. The YBaCuO filler and γ-irradiation cause the polyimide transition from the amorphous state to the crystalline state, which is manifested in a sharp change in the spectrum in the range of ~2.3-3.9 eV. A significant increase in the extinction coefficient was found in the composite containing 0.50 wt.% of the filler that is associated with an increase in the radius of action of structurally active fillers on the macromolecules of the matrix. [ABSTRACT FROM AUTHOR]

One of the biggest unsolved problems in condensed matter physics is what mechanism causes high-temperature superconductivity and if there is a material that can exhibit superconductivity at both room temperature and atmospheric pressure. Among the many important properties of a superconductor, the critical temperature (T c) or transition temperature is the point at which a material transitions into a superconductive state. In this implementation, machine learning is used to predict the critical temperatures of chemically unique compounds in an attempt to identify new chemically novel, high-temperature superconductors. The training data set (SuperCon) consists of known superconductors and their critical temperatures, and the testing data set (NOMAD) consists of around 700,000 novel chemical formulae. The chemical formulae in these data sets are first passed through a collection of rapid screening tools, SMACT, to check for chemical validity. Next, the DiSCoVeR algorithm is used to train on the SuperCon data to form a model, and then screens through batches of the formulae in the NOMAD data set. Having a combination of a chemical distance metric, density-aware dimensionality reduction, clustering, and a regression model, the DiSCoVeR algorithm serves as a tool to identify and assess these superconducting compositions (Baird et al., 2022). This research and implementation resulted in the screening of chemically novel compositions exhibiting critical temperatures upwards of 150 K, which correlates to superconductors in the cuprate class. This implementation demonstrates a process of performing machine learning-assisted superconductor screening (while exploring chemically distinct spaces) which can be utilized in the materials discovery process. [Display omitted] [ABSTRACT FROM AUTHOR]

• This study is the first in which a HTS induction/synchronous motor (HTS-ISM) with REBCO bulk superconductors has been successfully designed, tested, and fabricated. • The critical current of the REBCO bulk sample was investigated by applying a magnetic field perpendicular to the top surface at 77 K. • The no-load test at 77 K confirmed that the prototype could attain synchronous speeds at various frequencies. • The differences between the HTS-ISM using REBCO bulk bars and the HTS-ISM utilizing REBCO tapes per bar in the no-load and load tests are summarized. Lightweight and highly efficient high-temperature superconducting (HTS) rotating electric machines show great potential for transportation applications. An advantage of RE-Ba-Cu-O (REBCO, where RE=rare earth) bulk superconductors over stacked HTS tapes is their ability to carry larger and more homogenous currents. This study is the first in which an HTS induction/synchronous motor (HTS-ISM) with Gd-Ba-Cu-O (GdBCO) bulk superconductors has been successfully designed, fabricated, and tested. Our fabricated prototype featured a squirrel-cage rotor wound with 44 GdBCO bulk bars that were embedded in the rotor iron and connected at both ends using Y-Ba-Cu-O (YBCO) tapes to form a short circuit. First, the critical current of the bulk sample was investigated under a magnetic field perpendicular to its top surface at 77 K. Subsequently, no-load and load tests were performed in liquid nitrogen at different frequencies to verify the performance of the prototype. Finally, we thoroughly analyzed the differences between the proposed HTS-ISM that utilizes GdBCO bulk bars and developed HTS-ISMs that utilize a few turns of YBCO or Bi-Sr-Ca-Cu-O (BSCCO) tapes per bar. [ABSTRACT FROM AUTHOR]

The present study aims to reduce the outer radius of the central solenoid (CS) with respect to its nominal size specified by EUROfusion for a maintained CS magnetic flux. A reduced outer CS radius would allow the reduction of the overall size and cost of the DEMO magnet system. The proposed outline design of the winding pack for the CS1 module is based on layer winding. To achieve the same magnetic flux in a CS coil of significantly reduced outer radius the peak magnetic field at the CS conductors needs to be substantially increased. The use of high-temperature superconductors is therefore envisaged in the highest field sections of the CS coil. It is planned to use react & wind Nb 3 Sn conductors for intermediate field sections and NbTi at the lowest fields. In order to make a most economic use of the superconductors the proposed winding pack design considers a superconductor grading. [ABSTRACT FROM AUTHOR]

In this paper, a high force density, high-temperature superconductor dual-stator tubular Vernier machine (HTS-DSTVM) has been proposed for wave energy extraction. The machine adopts dual-stator configuration with spoke-type permanent magnets on the translator. The inner stator does not have any winding, and HTS bulks are placed between the adjacent flux modulation teeth of the inner stator to decrease the leakage flux and improve the force density. The HTS bulks effectively shield the leakage flux of the proposed HTS-DSTVM to improve the force density and power factor. 2-D finite-element method results validate that the proposed HTS-DSTVM yields a higher thrust force density per magnet volume and higher power factor compared with the recently presented flat dual-stator spoke-type linear Vernier machine due to the leakage flux shielding effect of HTS bulks. [ABSTRACT FROM AUTHOR]

Ever since high- T c superconductivity was found in H 3 S at 203 K under 200 GPa pressure, researches on hydrogen-rich family including H 3 S, H 3 P, and H 3 Te have been intensively carried out. Among those compounds, H 3 Se is a promising candidate of the same space group with H 3 S. In this work, we have thoroughly studied the electronic and phonon structures of H 3 Se using density functional theory (DFT) calculations. It is demonstrated that the electronic bands of H 3 Se contain van Hove singularities near the Fermi energy, which play a significant role in the superconductivity of this material. Besides, an accurate tight-binding model is proposed based on the Wannier function interpolations which can capture the main features of the electronic structures of H 3 Se. Moreover, we have also discussed the phonon dispersions and vibration modes for a better understanding of the phonon–electron interaction in H 3 Se. [ABSTRACT FROM AUTHOR]

Copyright of Electrical Engineering & Electromechanics is the property of National Technical University, Kharkiv Polytechnic Institute and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

This paper proposes a new high-temperature superconductor (HTS) dual-rotor flux-switching machine for direct-drive wind energy conversion. The key is to adopt dual-rotor structure to improve utilizations of the HTS excitation field and the machine space, thus achieving a high power density. Also, the HTS excitation can easily achieve flexible flux regulation to keep armature voltage constant under time-varying wind speeds. The operation principle, with emphasis on the effect of relative position of both rotors on the magnetic circuits, is described in details. And the initial machine design, especially the split ratio optimization, has been done. By using the finite element analysis, the machine performances are analyzed, and its validity is verified. [ABSTRACT FROM PUBLISHER]

In this paper, we have calculated the dependence of critical current density j c on the radius R and concentration of extended ferromagnetic defects in the system simulating a high-temperature superconductor (HTSC) layer. It was shown that at fixed volume concentration of ferromagnetic fraction the j c (R) dependence, as against nonmagnetic defects, has one maximum or two maxima at certain magnetization values of ferromagnetic fraction. We found that these maxima are due to the interplay of two parameters: concentration and effective depth of potential wells of defects. [ABSTRACT FROM AUTHOR]

The high-speed method is proposed for analyzing a shielding current density in a high-temperature superconducting film containing cracks. In the proposed method, the linear-system at each iteration of Newton method is solved by using a GMRES(k) method. Consequently, it is found that the GMRES(k) method is a powerful tool for analyzing the shielding current density in an HTS thin film. In addition, the speed of the GMRES(k) method can be accelerated by a factor of about 2 by using the H-matrix method. [ABSTRACT FROM AUTHOR]

The aging effects in YBa 2 Cu 3 O 6+ δ have been investigated on the low-speed quenched samples in contrast to other similar studies where the high-speed quenched samples were examined. In the framework of the investigation, XPS analysis has been conducted for the samples stored after quenching for the specified times τ and a detailed experimental dependence of the YBa 2 Cu 3 O 6+ δ lattice parameters a , b , and c on both δ and τ has been obtained. The regime of low-speed quenching results in a threefold increase in the aging effect magnitude. Particular cases of the c ( δ ; τ ) dependence are well described by a second-order polynomial with applying different coefficients for different τ . The behavior c has been explained on the basis of a simple model of the Coulomb interaction between the CuO 2 and CuO δ structural planes, in which the hole charge transfer from CuO δ to CuO 2 takes place providing the standard level of T c in YBa 2 Cu 3 O 6+ δ (this level is characterized by a maximum T c of 93 K at δ = 0.9). It has been demonstrated that the c ( δ ; τ ) dependence is a good alternative to assessing the hole concentration in YBa 2 Cu 3 O 6+ δ . By analyzing the c ( δ ; τ ) experimental dependence as well as the data on the hole localization in the pairs Cu O obtained by XPS, the authors have made a conclusion about the nature of observed aging effects. The latter are likely to be related to the transition of the Cu 3 d 9 L −1 electron configuration to Cu 3 d 8 for copper in the basal plane of YBa 2 Cu 3 O 6+ δ at RT. [ABSTRACT FROM AUTHOR]

This paper presents a finite element model based on the H -formulation to solve the electromagnetic behavior and AC loss in rectangular bulk superconductor with an elliptical flaw in AC external field condition. Both the interior flaw and the edge flaw are considered. A modified E – J power law which is valid for an arbitrary current density range is adopted in order to predict the strong local enhancement of the current density in the vicinity of the flaw tip. The results for the usual E – J power law are calculated for comparison as well. The simulation results show that the existence of the flaw significantly blocks the flow of the induced current and forces the current to redistribute around it. Meanwhile, the strong local enhancement of the current density is observed in the vicinity of the flaw tip. Furthermore, the influences of the size and position of the flaw on the local enhancement of the current density in the vicinity of the flaw tip are investigated. In addition, it is found that the influence of the flaw on the AC loss of the sample is slight for both cases of the interior flaw and the edge flaw. [ABSTRACT FROM AUTHOR]

BiSrCaCu O (Bi-2212) polycrystalline bulks with Ag nanoparticles inclusion content of x = 0, 0.125, 0.250 and 0.500 wt% were fabricated by spark plasma sintering process. Bi-2212 precursor powders were synthesized by modified coprecipitation process Ag nanoparticles with the particle size of 5 ∼ 20 nm were synthesized by a microplasma reduction method. The influences of Ag inclusions on the textural structures and related superconducting properties were systematically investigated. Both XRD and XPS results revealed the elemental state of Ag in the bulks. Therefore, no doping effect was observed on the lattice parameters, as well as the critical temperature of Bi-2212 phase. Obvious enhancements of texture structures and increase of average grain size were obtained due to the change of crystallization behavior of Bi-2212 with Ag doping. Thus, intergrain connections were obviously improved, which contributed to the increase of self-field critical current density. Besides, the formation of better crystallized grain boundaries increased the number of effective pinning centers, thus enhanced the flux pinning properties and the in-field transport properties. Based on the influences mentioned above, improvement of critical current density of over 60 % was obtained with the optimal Ag content of 0.250 wt %. [ABSTRACT FROM AUTHOR]

The chemical stability of the powder DyBa 2 Cu 3 O 6+δ has been studied by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and thermal analysis at ambient conditions. The powder was subjected to mechanical processing in a ball mill-activator to accelerate chemical degradation. The kinetic regularities of hydrolytic decomposition of DyBa 2 Cu 3 O 6+δ under the influence of air moisture have been determined. The resistive properties of DyBa 2 Cu 3 O 6+δ to water have been found to be better, but not much different from analogous properties of YBa 2 Cu 3 O 6+δ which is unstable in a wet environment. Chemical degradation of the material is triggered by crucial concentrating of water particles near the free surface of the solid reactant (due to their low diffusibility in the bulk) leading to rapid chemical decomposition of the respective regions. [ABSTRACT FROM AUTHOR]

Single-domain YBCO superconductors with different additions of nanometer Y Ba CuNbO (YNb2411), based on the solid phase of [(100- x)Y BaCuO (Y211) + x YNb2411] ( x = 3, 5, 7, 10, 12) and liquid phase of (Y211 + 9BaCuO + 6CuO), were successfully fabricated by a modified top seeded infiltration and growth process (TSIG), the growth morphology, microstructure, levitation force and the trapped magnetic field were investigated in details. Results indicate that single-domain YBCO superconductors can be fabricated with x ≤ 7 wt % but random nucleation of YBCO crystal occurs near the edge of the sample and seriously reduced the size of the single domain grown from the NdBCO seed when x ≥ 10 wt %. The YNb2411 particles were successfully introduced into the YBCO matrix, and the size of the YNb2411 particles embedded in the YBCO matrix is about 300 nm. However, agglomeration usually occurs when the addition of YNb2411 ≥ 10 wt %. As a result, the levitation force increases firstly from 32 to 42.5 N and then reduces down to 7 N with the increasing of YNb2411 additions from 3 to 7 wt % and 12 wt %. The results are helpful to improve the properties of YBCO bulk superconductors. [ABSTRACT FROM AUTHOR]

From the perspective of practical application, chemical solution deposition (CSD) technology is promising for the preparation of superconductor/insulator/superconductor (SIS) junctions with YBa2Cu3O7-x films as the superconducting layers compared with the various vacuum deposition processes currently used. In this study, trilayer films of YBa2Cu3O7-x/SrTiO3/YBa2Cu3O7-x were prepared using the CSD method. It was observed that when the nominal thickness of the interlayer (SrTiO3) was 14 nm, the I-V curve of the structure was similar to that of a weak-link Josephson junction due to the predominant weak links of microbridges and point contacts. When the nominal thickness of the interlayer was 40 nm, the I-V curve exhibited hysteresis due to the predominant tunnel effect. When the nominal thickness of the interlayer was 120 nm, the various weak links for superconducting coupling were absent, and the resistivity between the two YBa2Cu3O7-x layers was 3.4×107 Ω cm, which can satisfy the requirements for isolating electrodes in superconducting electron devices. [ABSTRACT FROM AUTHOR]

To realize antenna-coupled terahertz (THz)-wave oscillators using intrinsic Josephson junctions, rectangular mesas, 98-158 μm long, 78 μm wide and 1.04 μm high were fabricated on a BiSrCaCuO high-temperature superconductor, and the cavity resonant modes in the mesas were evaluated based on their radiative frequencies. For appropriate bias voltages in the return curve of an I-V characteristic of a 138-μm-long mesa, two peaks in the radiative power were observed. At the voltages where the peaks first appeared at high and low biases, frequencies of 0.646 and 0.499 THz were measured using a lamellar interferometer. The cavity modes corresponding to these two frequencies are TE and TE modes, respectively. The temperature and size dependencies of the calculated resonant frequencies based on a 3D cavity model agree with measurements, validating the mode assignments. [ABSTRACT FROM AUTHOR]

Twist plays an important role to impart tensile strength in yarn during the spinning process. In the most widely used ring-spinning machine for short staple yarn production, a combination of ring and traveler is used for inserting twist and winding the yarn on cops. The main limitation of this twisting mechanism is the friction between the ring and traveler, which generates heat at higher speed and limits the productivity. This limitation can be overcome by the implementation of a magnetic bearing system based on superconducting technology, which replaces completely the existing ring/traveler system of the ring-spinning machine. This superconducting magnet bearing consists of a circular superconductor and permanent magnet ring. After cooling the superconductor below its transition temperature, the permanent magnet ring levitates and is free to rotate above the superconductor ring according to the principles of superconducting levitation and pinning. Thus the superconducting magnetic bearing (SMB) ensures a friction-free operation during spinning and allows one to increase spindle speed and productivity drastically. The yarn properties using the SMB system have also been investigated and they remain nearly identical to those of conventional ring yarns. [ABSTRACT FROM PUBLISHER]

• I c degradation under transverse stress for Bi-2212 round wires was investigated. • Sample sintered at atmosphere with annealing has the best fatigue performance. • The greater transverse fatigue stress will accelerate the process of fatigue. Bi-2212 multi-core round wires without anisotropy can be made into Rutherford cable and cable-in-conduit conductor (CICC) using traditional cable winding technology, which has been widely used in high-field magnets such as fusion reactors. Recently, Bi-2212 is considered to be one of the most promising potential superconducting magnet materials in the Chinese Fusion Engineering Test Reactor (CFETR) magnet. However, Bi-2212's ceramic structure and Ag/Mg alloy sheath make it susceptible to stress. Due to the complicated working environment of magnet, Bi-2212 round wire is bound to be affected by cyclic electromagnetic stress and thermal stress. Several researchers have reported the performance of Bi-2212 round wire under axial tension strain and tension fatigue. And the impact of indentation on the critical current of Bi2212 round wire has been studied. However, the study of transverse stress characteristics has not been reported. In this work, critical current degradation under cyclic transverse stress for Bi-2212 round wires prepared by different heat treatment processes was studied. The initial critical current I c0 at 77 K for sample sintered at overpressure with annealing was the highest and I c0 for sample sintered at atmospheric pressure without annealing was the lowest. The greater transverse fatigue stress will accelerate the process of fatigue. [ABSTRACT FROM AUTHOR]

The applications of high-temperature superconductor (HTS) filters or subsystems to radio astronomy, the third generation (3G) mobile communications, meteorological radar, and satellite are introduced. A wideband HTS filter for the Miyun 50-m radio telescope in Beijing was presented, and a novel resonator and a new style interleaved coupling structure were proposed for the design of the wideband filter. An HTS transceiver subsystem was constructed. A field trial in commercial TD-SCDMA base station network was carried out in Beijing and remarkable improvements were achieved for RF performance in both transmitting and receiving chains. A demonstration HTS meteorological radar station was set up in Beijing and it showed great enhancements in sensitivity and anti-interference ability in urban area wind profile measurements. An experimental HTS microwave receiver front end for satellite applications had been constructed and passed all the space qualification tests. As a payload of an experimental satellite, it was ready for launch. [ABSTRACT FROM AUTHOR]

Abstract: Theoretical methods of calculating of two-dimensional magnetic fields, inductive parameters and output characteristics of the new type of high-temperature superconducting (HTS) synchronous motors with a composite rotor are presented. The composite rotor has the structure containing HTS flat elements, permanent magnets and ferromagnetic materials. The developed calculation model takes into account the concentrations and physical properties of these rotor elements. The simulation results of experimental HTS motor with a composite rotor are presented. The application of new type of HTS motor in different constructions of industrial high dynamic drivers is discussed. [Copyright &y& Elsevier]

Ultra-fast THz detectors from superconducting YBaCuO (YBCO) thin films were developed to monitor picosecond THz pulses. YBCO thin films were optimized by the introduction of CeO and PrBaCuO buffer layers. The transition temperature of 10 nm thick films reaches 79 K. A 15 nm thick YBCO microbridge (transition temperature-83 K, critical current density at 77 K-2.4 MA/cm) embedded in a planar log-spiral antenna was used to detect pulsed THz radiation of the ANKA storage ring. First time resolved measurements of the multi-bunch filling pattern are presented. [ABSTRACT FROM AUTHOR]

The modified basis functions of element-free Galerkin (EFG) method generated by weight function control of moving least-squares interpolants for an axisymmetric problem are investigated. In the axisymmetric problem, a physical quantity of rotating angle direction on the symmetry axis should be zero. By using standard EFG, however, the values on symmetric axis are non zero because the axisymmetric is not considered in basis function. In order to clear up the above problem, the modified basis function of EFG is proposed. The numerical simulation of shielding current density in axisymmetric high-temperature superconductor is adopted for practical applications of modified axisymmetric EFG. The results of computations show that the shielding current density on symmetric axis vanish in both cases. In addition, the experimental critical current density measurement method is reproduced numerically by using the numerical code. [ABSTRACT FROM AUTHOR]

Abstract: In the present work, the distributions of the stress induced by flux pinning in a cylindrical superconductor with a concentric elliptic hole are studied. The Kim model is considered for the critical state, and the analytical expression of the stress in the cylinder is derived when the concentric hole is circular. Based on the finite element method, at first, the validity of the calculation process and the accuracy of the numerical results are proved by comparing with the analytical results. Subsequently, the distributions of the stress are obtained for different ratio of the major axis and the minor axis of the elliptic hole. It is found that due to the effect of stress concentration, as the value of ratio the major axis and the minor axis becomes large, the radial and hoop stress in superconductor just increase significantly in the vicinity of the hole, and the variation of the hoop stress is more sensitive. These results have significant effects on the safety in applications of superconductor. [Copyright &y& Elsevier]

The crystal defects of the nano-scale, which are called artificial pinning centers (APCs), were successfully introduced into high-temperature superconductors (HTS) by nanotechnology, in order to strongly pin the quantized vortices. Critical current densities Jc of the HTS films were dramatically improved by APCs whose dimensions were controlled. By this method, the in-field Jc (77 K) of the high-quality, epitaxial films was improved by one order of magnitude or more compared with the values of the past. A current outline of the research is described in this paper. [ABSTRACT FROM AUTHOR]

For high speed and low cost production of coated conductors, a simplified 4-layered buffer architecture consisting of Gd2Zr2O7 (GZO)/Ion Beam Assisted Deposition (IBAD)-MgO/LaMnO3/CeO2 was realized, which is compared with the conventional 5-layered IBAD-MgO buffer layers. A new cation diffusion barrier and nucleation GZO layer was first reported. The fourth layer of Pulsed Laser Deposition (PLD)-CeO2 showing the self-epitaxial growth effect resulted in the in-plane texturing (Δφ) of about 3 to 4 degrees. Consequently, high critical current, Ic, values above 600 A/cm-width were attained for PLD-GdBa2Cu3O7-x (GdBCO) short samples. Using this result, a 41 m long GdBCO coated conductors was successfully fabricated at the production rate of 24 m/h for IBAD-MgO. This conductor exhibited superior Δφ values of 3.7 to 3.8 degrees and high Ic values of 500 to 600 A/cm-width at 77 K and self -field (s.f.) along almost the entire length. The highest Ic recorded 608 A/cm-width with the Jc value of 2.43 Ma/hboxcm2. Furthermore, a new IBAD-MgO deposition method was developed, using DC-reactive sputtering which is expected to be inexpensive and easy to scale up. This system brought about a high production rate of 150 m/h in spite of the small deposition area (6 x 20 cm2). The GdBCO on this buffered substrate also showed a high Ic value of 286 A/cm-width at 77 K and s.f., corresponding to the Jc value of 1.43 2 Ma/hboxcm2. [ABSTRACT FROM AUTHOR]

It is well known that the levitation force and stability of superconducting levitation devices are strongly dependent on the properties of its components, such as the geometry, dimensions, cooling process or critical-current density of the superconductor. In this work we study these dependences in levitating systems consisting of a superconductor and a permanent-magnet guideway with translational symmetry. Using a model based on the critical state approximation and a magnetic-energy minimization procedure, we analyse for the field and zero-field cooling cases, the influence of some parameters of the system, such as the width and the critical-current density of the superconductor and the height of the permanent magnets, on the levitation force and stability. From the calculated results we provide hints of how, by modifying some features of the systems, one can optimize either the levitation force, or the stability, or a combination of both. [ABSTRACT FROM AUTHOR]

The influence of the stable temperature rise induced by current charging on the current-carrying capacity of a high-temperature superconductor without stabilizing matrix is investigated. Two characteristic values of the electric field at which the convective and conductive heat transfer mechanisms mostly affect the formation of current charging states in the superconductor are defined. It is shown that its stable temperature preceding the onset of current instability not only is always above the coolant temperature but also increases with decrease in these characteristic electric fields. As a result, the current stability conditions are modified due to the thermal peculiarities of the current charging formation of stable electrodynamics states of the superconductor. Namely, the allowable stable values of electric field and current can be below or above those determined by a priori chosen critical parameters of the superconductor. The criteria allowing one to estimate the boundary of existence of these stability areas (sub-critical and over-critical) are written taking into account the size effect. The performed analysis reveals that the temperature-dependent heat capacity of superconductor leads to such shape of its voltage-current characteristics, which has only the positive slope during continuous current charging both before and after current instability onset. It is also proved that the thermal degradation of the current-carrying capacity of superconductor occurs in the sub-critical area. Due to this effect, the currents flowing stably in the superconductor are not only obviously less than the corresponding critical current, but also not increase proportionally to increasing cross-sectional area of superconductor or to its critical current density. These effects must be considered in investigations of current-carrying capacity of superconductors. [ABSTRACT FROM AUTHOR]

In this research, reflectance spectra for a one-dimensional (1D) photonic crystal (PC) consists of a high-temperature superconductor Hg-1223 and a semiconductor GaAs have been calculated using the well-known transfer matrix method (TMM) and the two-fluid model. The proposed PC was introduced as an optical pressure sensor at the mid-IR region. The pressure effect is studied on two types of PCs; a defective PC [Air (GaAs/Hg 1223)5 (GaAs) (GaAs/Hg 1223)5 substrate] and periodic PC [Air (GaAs/Hg-1223)10 substrate]. Herein, we have found that the pressure sensitivity reached a high value of 1.7467 nm/GPa at an applied pressure of 6 GPa. However, a small blue shift is noticed for the periodic design. Therefore, the number of periods, thickness, and incident angle were taken after many optimization steps to get the highest-pressure sensitivity for the defective PC. Based on the optimization process, the results reveled higher performance for the other sensitivity parameters such sensor resolution, signal to noise ratio, figure of merit, and quality factor (QF). Finally, we have studied the effect of the operating temperature on the defect mode, which shows a small redshift with increasing the operating temperature. We hope this research may be utilized for applications of tunable filters and hydrostatic pressure sensors. [ABSTRACT FROM AUTHOR]

Abstract: The stellarator WENDELSTEIN 7-X (W7-X) and the satellite tokamak JT-60SA will use High Temperature Superconductor (HTS) current leads to reduce cryogenic load and operational cost. Forschungszentrum Karlsruhe is in charge of design, construction and test of these HTS current leads. For W7-X fourteen current leads with a nominal current of 14kA and a maximum current of 18.2kA are required that are oriented upside down with the room temperature end at the bottom. JT-60SA is constructed in the frame of the Broader Approach Agreement and will use 26 current leads mounted in vertical, normal position with room temperature end at the top. All current leads will consist of an HTS part using Bi-2223 conductor and a classical Cu heat exchanger. The Cu heat exchanger covers the range between 60K and room temperature and will be cooled with 50K He while the HTS part is conduction cooled, only. For simplicity a common basic design of the current leads for W7-X and JT-60SA is planned which requests that the current leads work independently of the orientation, and from the experimental boundaries given by W7-X and JT-60SA the current leads have to withstand a loss of He coolant for more than 10min and allow a discharge of the magnet system although a quench of the HTS part has happened. JT-60SA gives the more critical HV requirement with a Paschen tight insulation of 21kV. All current leads shall be designed for low thermal loads, under full current and in standby mode. The paper will give details of the actual design status of these current lead developments for W7-X and JT-60SA based on a common basic design. [Copyright &y& Elsevier]

This paper consists of two parts: (1) mechanism of formation of hole-pairs and quantum stripes in cuprate superconductors, and (2) resistivity versus temperature variation in YBa2 Cu3O7-δ superconductor with different doping levels in the range 400–Tc. (1) On deoxygenation, CuO2 plane of high-temperature cuprate superconductors are broken into small magnetically isolated fragments, predominantly Cu-tetramer (CuO)4. Its electron paramagnetic resonance spectra show fine and hyperfine splittings. It was concluded that these splittings are due to FM coupling of the electronic spins of the four holes on the four Cu-ions in (CuO)4 as well as the FM coupling of the nuclear spins of the four Cu-ions. A magnetic field is generated perpendicular to CuO2 plane due to the spin magnetic moment of four holes and their orbiting around the (CuO)4 frame. In the nondeoxygenated superconductors, this magnetic field leads to the formation of quantum stripes of free charge carriers and in special cases to the formation of preformed hole-pairs. This is the first model of a hole-pair, though its existence has been conjectured from various experimental results. (2) The electrical conduction in superconductors along c-axis seems to arise from the movement of free holes and along a-axis from the parallel combination of resistivities arising from the movement of free holes and paired holes, but no single formula connecting ρ and T is applicable to explain resistivities either along c- or a-axis in the entire temperature range. Nature of charge carriers seems to change continuously as the temperature is lowered. In the range 200–Tc, both along the c- and a-axes, the experimental resistivities depart significantly from those calculated by the formula applicable in the range 400–200 K. Plausible explanation has been suggested for the departure of experimental resistivities from the calculated ones in the low temperature region. [ABSTRACT FROM AUTHOR]