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Step edge Josephson junction devices of YBa2Cu3O7‐x films on SrTiO3 substrates are fabricated, and the device performance is studied for different t/h (t: the thickness of the film, h: step height) ratios. After depositing YBCO films on the step etched substrates, photolithography, and ion beam etching techniques are used to fabricate three devices with t/h ratios of ≈0.4, 0.7, and 1.2. The critical temperatures (Tc) of the devices are ≈82, 85, and 88 K, respectively. The critical current (Ic) and normal state resistance (Rn) are observed to be t/h ratio dependent. The critical current values at 70 K for the devices with t/h ratios of 0.4, 0.7, and 1.2 are ≈425, 550, and 820 μA, respectively. The IcRn product at 70 K is ≈2.06, 2.76, and 0.43 mV for t/h ratios 0.4, 0.7, and 1.2, respectively, which indicates that the t/h ratio of 0.7 is optimum for the device performance. The current versus voltage curves at 68 K are fitted using the resistively shunted junction model using the Portable Superconducting Circuit Analyzer (PSCAN2) simulator, which suggests that there can be normal conducting links present across the microbridge, and it becomes effective for I > Ic, contributing to excess current. [ABSTRACT FROM AUTHOR]

In this manuscript, a miniature high-temperature superconductor (HTS) bandpass filter (BPF) with multi-transmission zeros (TZs), high selectivity, and great attenuation of stopband is presented. A couple of dual-mode resonator (DMR) is employed to achieve the proposed BPF, which can be characterized by using the classical even-odd mode analysis technique. The presented cascaded DMR can excite four resonant modes, which can be individually managed. Plus, a pair of intrinsic transmission zeros can be yielded at both the lower and upper edges of the passband, which results in sharp shirt performance. As an example, the HTS BPF is designed, fabricated, and tested, in which the center frequency is centred at 3.95 GHz and the 3-dB fractional bandwidth (FBW) is 2.5%. The proposed HTS BPF is implemented by using Tl2Ba2CaCu2O8 (Tl-2212) thin films which are fabricated by two-step processing and the superconducting critical temperatures (Tc) of the HTS films can reach 103 K. The design methodology is confirmed since the experimental results are in good agreement with theoretical results, showing desired bandpass characteristics, high selectivity, and the attenuation of lower and upper stopbands above −50 dB. Further, the circuit size is only 0.4 cm2. [ABSTRACT FROM AUTHOR]

The degree of orientation of mixed a‐ and c‐axis‐oriented epitaxial thin films was defined. This can be evaluated using several scanning methods in X‐ray diffraction. Reciprocal space mapping was chosen because it is adaptable to the modulations of lattice spacing, as well as the small modulations of orientation. The proposed method was demonstrated for superconducting YBa2Cu3O7–δ and magnetic FePt thin films. The increasing tendency of the degree of orientation with increasing deposition temperature agreed with those obtained from the pole figure measurements. The degree of orientation was used to evaluate the order parameter of the FePt film with overlapping sublattice and fundamental peaks. © 2024 Institute of Electrical Engineers of Japan and Wiley Periodicals LLC. [ABSTRACT FROM AUTHOR]

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]

A performance evaluation system (PES) can experimentally test the structural stability and magnetic field effects of HTS coils against high magnetic fields and electromagnetic forces before mounting the HTS coils on a large-capacity rotating machine. This paper deals with the characteristic analysis of electromagnetic force in an HTS field coil for a 10 MW Class HTS Wind Power Generator using PES. Based on the designed 10 MW class HTS wind power generator, the HTS coils are manufactured and installed in the PES by a support structure, which is designed considering the electromagnetic force (torque) and heat loads in the HTS coil. To check the stress and deformation in the support structure caused by the electromagnetic force generated from the coil, strain gauge sensors were attached to the support structure and measured under full-load conditions. As a result, the maximum magnetic field and electromagnetic force are 2.8 T and 71 kN, respectively. Compared to the analysis results, the magnetic field and generated electromagnetic force in the HTS coil were the same under no-load and full-load conditions. These results will be effectively used to study and fabricate high magnetic field coils for HTS applications, as well as the PES being fabricated. [ABSTRACT FROM AUTHOR]

Polarized neutron reflectometry is an experimental method for studying metallic thin heterophase layered materials, polymer films, biological systems, the free surfaces of liquids, and magnetic fluids. It requires experimental equipment that includes a special magnetic system. The magnetic system described in this work, a vector magnet, will allow one to change the direction of the magnetic field in three directions, to place a temperature-control device inside at low and ultra-low temperatures, and will have an aperture that allows one to place a system for detecting neutrons and gamma rays outside. According to calculations, the cryomagnet will allow the application of a maximum field in the vertical plane of up to 3 T, and in the horizontal plane of up to 1 T. To manufacture a vector magnet, in this work, it is proposed to use a tape made of a high-temperature superconductor with a width of 4 mm. A cryostat with a vector magnet will be installed at the REMUR reflectometer on the eighth channel of the IBR-2 reactor. [ABSTRACT FROM AUTHOR]

The detection of inelastically scattered soft x-rays with high energy resolution usually requires large grating spectrometers. Recently, photoelectron spectrometry for analysis of x-rays (PAX) has been rediscovered for modern spectroscopy experiments at synchrotron light sources. By converting scattered photons to electrons and using an electron energy analyser, the energy resolution for resonant inelastic x-ray scattering (RIXS) becomes decoupled from the x-ray spot size and instrument length. In this work, we develop PAX towards high energy resolution using a modern photoemission spectroscopy setup studying Ba2Cu3O4Cl2 at the Cu L 3-edge. We measure a momentum transfer range of 24% of the first Brillouin zone simultaneously. Our results hint at the observation of a magnon excitation below 100 meV energy transfer and show intensity variations related to the dispersion of dd -excitations. With dedicated setups, PAX can complement the best and largest RIXS instruments, while at the same time opening new opportunities to acquire RIXS at a range of momentum transfers simultaneously and combine it with angle-resolved photoemission spectroscopy in a single instrument. [ABSTRACT FROM AUTHOR]

Topological photonics has been widely investigated due to its profound physical significance and great number of potential applications. Microwaves have long wavelengths, so it is relatively easy to manufacture large-sized microwave photonic crystals, enabling researchers to observe and measure phenomena such as topological boundary states. Nevertheless, the quality factors (QFs) of most resonators composed of traditional materials in the microwave region are relatively low, leading to topological edge states with high decay rates. In this study, we present a one-dimensional topological photonic crystal in the microwave region based on coupled superconducting resonators. A topological state with a QF as high as 6000 is observed, which proves this to be a new platform for the investigation of topological photonics with low decay rates in the microwave regime. [ABSTRACT FROM AUTHOR]

This paper presents a promising winding technique which enables higher power-densities in partially superconducting electrical machines with a slotless stator, e.g., self-supporting windings. Firstly, the formulation for defining the skewing factor of the helical winding is given. Afterwards, the skew angle and how diverse winding configurations can be characterised as a function of this angle is explained, along with different parameters such as the skewing factor, the harmonic content of the magnetomotive force wave in the airgap or the resistance per phase of the winding. The sine-shaped winding, a particular case of helical winding, is shown, with which, thanks to the benefits of the additive manufacturing, a better electromagnetic performance is achieved. Finally, the implementation of the helical winding configuration in a slotless partially superconducting 2 MW high-power and high-voltage electric machine for electric aircraft propulsion is assessed, comparing the machine active part weight and their power density.

A performance evaluation system (PES) can experimentally test the structural stability and magnetic field effects of HTS coils against high magnetic fields and electromagnetic forces before mounting the HTS coils on a large-capacity rotating machine. This paper deals with the characteristic analysis of electromagnetic force in an HTS field coil for a 10 MW Class HTS Wind Power Generator using PES. Based on the designed 10 MW class HTS wind power generator, the HTS coils are manufactured and installed in the PES by a support structure, which is designed considering the electromagnetic force (torque) and heat loads in the HTS coil. To check the stress and deformation in the support structure caused by the electromagnetic force generated from the coil, strain gauge sensors were attached to the support structure and measured under full-load conditions. As a result, the maximum magnetic field and electromagnetic force are 2.8 T and 71 kN, respectively. Compared to the analysis results, the magnetic field and generated electromagnetic force in the HTS coil were the same under no-load and full-load conditions. These results will be effectively used to study and fabricate high magnetic field coils for HTS applications, as well as the PES being fabricated.

High-temperature superconductors such as REBa2Cu3O7-x (REBCO, RE = rare earth) can generate strong magnetic fields that are promising for applications in particle accelerators and compact fusion reactors. Traditionally, voltage taps are installed in superconducting magnets to measure the voltage signals due to resistive transitions. The voltage-tap-based diagnostics is important for the development of magnet technology as it can help pinpoint the locations in the magnet windings that limit the magnet performance. The architecture of the multi-tape REBCO cable such as CORC wires, however, makes it difficult to apply the voltage-tap-based diagnostics to identify the locations of resistive transitions. Distributed fiber optic sensing (DFOS) has the potential to address this issue. In this paper, we report the measurements of thermal strain along a CORC wire based on optical frequency domain reflectometry with a maximum spatial resolution of 0.65 mm and a temporal resolution of 10 Hz. The optical fiber is co-wound with the CORC wire that is epoxy impregnated. During the test, current was increased until a resistive transition occurred in the conductor. The spectrum shift of the reflected light along the fiber was recorded. The results suggested that with proper thermal isolation from the cryogen, DFOS can be used to identify the locations of resistive transitions in CORC wires and magnets. The results will allow a better understanding of the causes of resistive transitions in REBCO conductors and magnets, which will help improve the REBCO magnet technology.

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]

This article studies the deformation resistance of high-temperature superconducting (HTSC) tapes for various parameters of deformation. The four-contact method has been used to measure the critical current in specimens deformed on indenters with diameters of 5–20 mm by tensile forces up to 200 N. The damage to the superconducting layer and local superconducting properties of mechanically impacted specimens have been investigated using scanning electron microscopy and scanning Hall magnetometry. [ABSTRACT FROM AUTHOR]

The paper describes a high-temperature superconducting magnetic system (HTS SMS) to equip an experimental stand intended for neuron activity researches under constant and low-frequency magnetic fields up to 1 T. The design of the magnetic system together with its electromagnetic and cryogenic parameters is briefly discussed. The test results of the preliminary experiments conducted in liquid nitrogen at 77 K for two interchangeable magnets are given. The first magnet was manufactured in the form of a double pancake coil wound with 4 mm high HTS tape. The second magnet was made of pure copper wire with no frame and was impregnated with a thermally conducting epoxy resin. The advantages of the HTS pancake coil were demonstrated in comparison with the cryo-resistive solenoid. Low energy consumption of the HTS magnetic system will allow conducting continuous non-invasive monitoring of biological objects in a magnetic field. [ABSTRACT FROM AUTHOR]

Possible macroscopic mechanisms for the destruction of the superconducting properties of a high-temperature YBa2Cu3O7-based superconductor cooled with liquid helium or nitrogen under input of AC are analyzed. It is shown that these mechanisms can be both of thermal and thermoelectrodynamic nature, which is based on the interrelated change in the electromagnetic field induced inside the superconductor and its temperature. Before the emergence of unstable states, intense stable energy dissipation can be observed, which is not taken into account in the current theory of losses. These mechanisms lead to stable supercritical values of the introduced current and the electric field induced inside the superconductor before the onset of instability and, consequently, high permissible overheating. The results discussed expand the scope of practical use of high-temperature superconductors. [ABSTRACT FROM AUTHOR]

With high efficiency and low energy loss, high-temperature superconductors (HTS) have demonstrated their profound applications in various fields, such as medical imaging, transportation, accelerators, microwave devices, and power systems. The high-field applications of HTS tapes have raised the demand for producing cost-effective tapes with long lengths in superconductor manufacturing. However, achieving the uniform and enhanced performance of a long HTS tape is challenging due to the unstable growth conditions in the manufacturing process. Although it is confirmed that the process parameters during the advanced metal organic chemical vapor deposition (A-MOCVD) process influence the uniformity of the produced HTS tapes, the high-dimensional process parameter signals and their complicated interactions make it difficult to develop an effective control policy. In this paper, we propose a local measure for the uniformity of HTS tapes to provide instant feedback for our control policy. Then, we model the manufacturing of HTS tapes as a Markov decision process (MDP) with continuous state and action spaces to assess the instant reward in real time in our feedback control model. As our MDP involves continuous and high-dimensional state and action spaces, a neural fitted Q-iteration (NFQ) algorithm is adopted to solve the MDP with artificial neural network (ANN) function approximation. The collinearity of process parameters can restrict our capability of adjusting the process parameters, which is addressed by the principal component analysis (PCA) in our method. The control policy adjusts the PCA of process parameters using the NFQ algorithm. Based on our case studies on real A-MOCVD dataset, the obtained control policy increases the average uniformity of tapes by 5.6% and performs especially well on sample HTS tapes with a low uniformity. [ABSTRACT FROM AUTHOR]

This paper presents the design of a 2 MW superconducting electric machine capable of replacing a conventional regional aircraft turbine. The main objective of this work is to advance in the path towards the more-electric aircraft, by incorporating and assessing in the same design technologies such as a superconducting rotor and its cooling by means of helium at cryogenic temperatures, the skewed armature winding or the oil-flooded cooling of the stator, to obtain high specific power density and efficiency values. Although the use of these technologies is well known in the literature, no work is found to implement all of them simultaneously, which poses great challenges both for their subsequent manufacture and later performance. After showing and justifying each element of the design of the electric machine, the electromagnetic performance of the motor and of the superconducting coils is assessed, it is thermally evaluated so that it does not exceed the strict temperature limits and a mechanical analysis of the elements of the motor is also carried out. The main finding of this work is the validation of the proposed model, and that, even though the designed engine is feasible at the proposed power level, the specific power density and efficiency values would improve in the case of upscaling the engine for implementation in larger aircraft.

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]

Topological photonics has been widely investigated due to its profound physical significance and great number of potential applications. Microwaves have long wavelengths, so it is relatively easy to manufacture large-sized microwave photonic crystals, enabling researchers to observe and measure phenomena such as topological boundary states. Nevertheless, the quality factors (QFs) of most resonators composed of traditional materials in the microwave region are relatively low, leading to topological edge states with high decay rates. In this study, we present a one-dimensional topological photonic crystal in the microwave region based on coupled superconducting resonators. A topological state with a QF as high as 6000 is observed, which proves this to be a new platform for the investigation of topological photonics with low decay rates in the microwave regime.

The article discusses the development of steady-state burning plasma in magnetic confinement fusion energy. It highlights the progress made in increasing the fusion triple product on tokamak devices, but notes that larger devices have not been built since the International Thermonuclear Experimental Reactor (ITER). However, advancements in physics and technology on tokamaks, such as the development of high-temperature superconductors, have shown promise for achieving breakthroughs in fusion energy. The article also discusses the potential benefits and challenges of strong magnetic fields in facilitating access to the burning plasma regime. Overall, the article suggests that the fusion field is entering a new stage of DT fusion with new opportunities and challenges. [Extracted from the article]

Ca-doped Bi-2201 samples obtained by optimized preparation methods increase the highest onset of superconducting transition T(c, onset) up to 77 K. Raman experiments show that Ca-doping makes the OSr peak shift from 643 to 647 cm−1, which indicates that the OSr and surrounding atoms become closer. In addition, pressure is used to amplify the effects of doping in the structural characterizations. High-pressure angle dispersive x-ray diffraction (ADXRD) results indicate that the Ca-doped Bi-2201 sample has a tighter atomic packing than the pure sample, which results in a lower Raman peak position shift rate under compression. Combining the ambient data with the high-pressure structural analysis, the apical oxygen of the CuO6 octahedron is closer to CuO2 plane and adjusts CuO2 plane distortion, resulting in the increasing of T(c, onset) in Ca-doped Bi-2201 samples. Highlights: The experimental strategy of using pressure to amplify the influence of Ca-doping on the structure of Bi-2201 phase was proposed. Ca-doped Bi2201 crystals have smaller lattice volume, shorter c-axis, and are less compressible than the pure phase. The influence caused by the apical oxygen of the CuO6 octahedron on distortion of CuO2 plane is an important reason for increasing the Tc of the Ca-doped samples. [ABSTRACT FROM AUTHOR]

In this work, we investigated the critical currents and pinning mechanisms in single crystals of the high-temperature superconductor Y123 with Mo substituted into CuO chains. The single crystals were annealed in oxygen at low (130–140 atm) and high (255 atm) pressure, which significantly influenced the observed properties. Magnetic hysteresis loops were measured at various temperatures in fields up to 14 T, for both H||c and H⊥c. On the basis of these measurements, the densities of critical currents were calculated using the Bean critical state model. Then, using the Kramer approach and the Dew-Hughes model, scaling of the pinning force was performed and the type of pinning centers and pinning mechanisms dominant in different field and temperature ranges were determined. Due to Mo substitution, the critical current density in single crystals annealed in oxygen under high pressure increased several times at lower temperatures, e.g., 3–4 times for T = 4–35 K and μ 0 H = 1–8 T, and by an order of magnitude at higher temperatures, e.g., for T = 65–75 K and μ 0 H = 2–3 T. For these single crystals, Δκ volume-like pinning centers (Mo2O11 octahedra dimers) and normal point-like pinning centers (interstitial oxygen) were identified as dominant at lower and higher fields, respectively. [ABSTRACT FROM AUTHOR]

The detection of inelastically scattered soft x-rays with high energy resolution usually requires large grating spectrometers. Recently, photoelectron spectrometry for analysis of x-rays (PAX) has been rediscovered for modern spectroscopy experiments at synchrotron light sources. By converting scattered photons to electrons and using an electron energy analyser, the energy resolution for resonant inelastic x-ray scattering (RIXS) becomes decoupled from the x-ray spot size and instrument length. In this work, we develop PAX towards high energy resolution using a modern photoemission spectroscopy setup studying Ba _2 Cu _3 O _4 Cl _2 at the Cu L _3 -edge. We measure a momentum transfer range of 24% of the first Brillouin zone simultaneously. Our results hint at the observation of a magnon excitation below 100 meV energy transfer and show intensity variations related to the dispersion of dd -excitations. With dedicated setups, PAX can complement the best and largest RIXS instruments, while at the same time opening new opportunities to acquire RIXS at a range of momentum transfers simultaneously and combine it with angle-resolved photoemission spectroscopy in a single instrument.

As the demand for eco-friendly energy increases, hydrogen energy and liquid hydrogen storage technologies are being developed as an alternative. Hydrogen has a lower liquefaction point and higher thermal conductivity than nitrogen or neon used in general cryogenic systems. Therefore, the application of hydrogen to cryogenic systems can increase efficiency and stability. This paper describes the design and analysis of a cryogenic cooling system for an electric propulsion system using liquid hydrogen as a refrigerant and energy source. The proposed aviation propulsion system (APS) consists of a hydrogen fuel cell, a battery, a power distribution system, and a motor. For a lab-scale 5 kW superconducting motor using a 2G high-temperature superconducting (HTS) wire, the HTS motor and cooling system were analyzed for electromagnetic and thermal characteristics using a finite element method-based analysis program. The liquid hydrogen-based cooling system consists of a pre-cooling system, a hydrogen liquefaction system, and an HTS coil cooling system. Based on the thermal load analysis results of the HTS coil, the target temperature for hydrogen gas pre-cooling, the number of buffer layers, and the cryo-cooler capacity were selected to minimize the thermal load of the hydrogen liquefaction system. As a result, the hydrogen was stably liquefied, and the temperature of the HTS coil corresponding to the thermal load of the designed lab-scale HTS motor was maintained at 30 K. [ABSTRACT FROM AUTHOR]

We present key design parameters of an innovative 10 MW low-speed direct-drive superconducting generator by high-temperature superconductor coated conductors for the rotor windings. In the simulations, the generator has an iron rotor with the superconducting coils operating at 20 K while the rotor core and the cooper stator are at room temperature. The calculations have been performed by Finite Element Software Comsol Multiphysics. Electromagnetic design parameters, magnetic flux distributions, phase current, voltage, and loss distributions of the superconducting generator are introduced. In addition, the AC losses that arise during the current increase in the superconducting rotor were calculated separately using both the H- and AV-formulation forms of Maxwell's equations employing the non-linear current–voltage relation of the superconductor. The current distribution and magnetic field distribution of the superconductor coils, volumetric loss density distribution, and comparison of the losses of each coil layer have been analyzed and discussed in detail. [ABSTRACT FROM AUTHOR]

Using the Monte Carlo method, the vertical z-component of levitation force acting on a thin HTS film in a field simulating the inhomogeneous field of a permanent magnet is calculated within the framework of a two-dimensional model of a layered HTS. The dependences of the vertical component of the levitation force on the distance to the magnet are obtained at different concentrations of pinning centers and at temperatures ranging from 1 to 50 K. A case is simulated in which a superconducting sample starts moving towards a magnet from infinity and then moves away from the magnet. The change of sign of the levitation force corresponds to the movement away from the magnet when trapped magnetic flux is present in the sample. The presence of hysteresis of the levitation force is demonstrated. It is also shown that the levitation force does not change its sign in a defect-free sample and in a sample with a large number of defects. This is due to the peculiarities of the distribution of vortex density and currents in the sample during magnetization process. [ABSTRACT FROM AUTHOR]

YBa 2 Cu 3 O y (Y-123) is one of the most intensively studied high-temperature superconductors (HTS) and has great potential for applications in electronics. Its superconducting properties significantly depend on the oxygen index (y), the peculiarities of the atomic crystal and microgranular structure, the type and concentration of contaminating atoms. Therefore, of particular interest are the techniques of HTS synthesis that significantly affect the superconducting properties, as well as modifications of these techniques. The aim of this study was to investigate the effect of ultrahigh dilution (UHD) technology on the Y-123 HTS properties. We applied UHD technology to treat Y 2 O 3 ·4BaO 2 ·6CuO composition (before and/or after calcination) and used solid-phase reaction to obtain batches of ceramic samples of the Y-123 phase. Main characteristics of the synthesized HTS specimens (the orthorhombic unit cell parameters, temperature dependence of electrical resistance, Meissner effect, and critical current density) were studied. X-ray phase analysis demonstrated that the samples were practically single-phase and consisted of the Y-123 phase. Depending on the treatment method, the modifying effect varied. Positive and most significant results were demonstrated for specimens obtained from precursor powder mixture treated with UHD. For some of such specimens an increase in the temperature of the beginning of the transition to the superconducting state by 3.8 K, the Meissner effect by 9%, and the density of the intergranular critical current by 35% were observed. We conclude that UHD technology can be used to improve properties of HTS. However, methodology for implementation of UHD technology should depend on which specific superconductor property needs to be changed. [ABSTRACT FROM AUTHOR]

This paper presents a review of the state of the art in electric propulsion for regional aircraft in the MW range. The implications surrounding the implementation of this technology, such as the need of high-power density or the use of high-voltage at high-altitude, are presented. Along with the challenges, the available technologies to face them are reviewed. Those are, as follows, the emerging new motor topologies for this purpose, the winding technologies, the materials employed for electric motors for aircraft propulsion and the ground-breaking use of high-temperature superconductors (HTS) as a high-power density enabler. Finally, a conclusion is presented gathering the main ideas of the paper.

Structure modulation of rare-earth barium cuperates (REBCO) superconducting films plays an essential role in the flux pinning behaviors. In this paper, nano-composite EuBa2Cu3O7−δ-BaHfO3 (EuBCO/BHO) films were deposited by the ultra-fast pulsed laser deposition technique. All nano-composite films exhibited high-quality orientation under the growth rates up to 100 nm/s. TEM cross-sectional analysis reveals that the EuBCO/BHO films have a distinct lamellar structure, which is related to the periodic change of growth conditions during the multi-turn dynamic deposition. In addition, the morphology of BHO varies with dopant content, which suggests a strong correlation between dopant content and the BHO self-assembly mechanism. Consequently, the vortex behavior shifts from giant-flux creep to vortex-glass formation at the thermally activated flux flow region as the dopant content increases. The primary flux pinning behaviors change from random to correlated pinning with the increase of dopant content at 4.2 K. Due to the larger contribution of the correlated pinning machinimas, the 8% BHO-doped EuBCO film exhibits the highest Jc value at 4.2 K, with moderate fields (below 8 T) among all the three films. At 4.2 K and 14 T, the 6% BHO doped EuBCO film has the highest Fp value attributing to the predominate random pinning mechanism.

In the process of manufacturing products from high-temperature superconductors (HTS), quality control must be carried out. Traditionally, for HTS coils, electrical tests are carried out to determine critical current. In the case of an unacceptable result, it is necessary to determine the cause. Therefore, it is necessary to develop nondestructive testing methods. This article proposes a technology for manufacturing quality evaluation. It is based on determining the actual location of the tape and the gaps between the turns and rows of the coil and analyzing these values. For this purpose, samples were scanned using computed tomography (CT) with a Nordson Dage XD7600NT X-ray inspection system with a μCT module. The obtained data were analyzed using VolumeGraphics VGStudio 2.2 software. Furthermore, the proposed technology can be used as part of a predictive analysis of the state of HTS coils in the windings of electrical machines. [ABSTRACT FROM AUTHOR]

In this study, we developed a superconducting magnetic bearing using a permanent repulsive magnet. A repulsive magnetic levitation system with a permanent magnet can generate a strong levitation force in the absence of a power supply. However, it is unstable, except in the direction of repulsion. In contrast, superconducting magnetic bearings can generate a restoring force in all directions by utilizing the magnetic flux pinning property of the superconductors. Therefore, we constructed a superconducting magnetic bearing (SMB), which is stable along all axes without control, and has a strong axial levitation force, by combining a repulsive-type magnetic levitation system and a superconducting magnetic levitation system. We also reduced the amount of HTS used for the SMB and proposed an efficient method of using HTS. Furthermore, a driving test of the flywheel incorporating the SMB was conducted to verify the characteristics of the SMB. The experiment confirmed that the flywheel could overcome the resonance and drive the flywheel. In the drive experiment, the flywheel was driven up to 10,000 rpm. [ABSTRACT FROM AUTHOR]

Subject and Purpose. The mechanism of destruction of the S-state of a nonlinear high-temperature superconductor as part of a coplanar waveguide has not been properly elucidated as the effect of avalanche-type transition to a highly dissipative state, which was experimentally detected by the authors, takes place. The present work is concerned with the development of an appropriate approach describing kinetics of destruction of the S-state of a nonlinear high-temperature superconductor in a coplanar waveguide with allowances made for an inhomogeneous distribution of the microwave current in the superconducting film strip. Methods and Methodology. Use of I.B. and O.G. Vendiks’ reasoning [2] is made on kinetics of the destruction of the superconducting state of a wide film when a direct current governed by the time-dependent Ginzburg-Landau equation is applied. Keeping unchanged their idea as to the S–N boundary forming in the film strip with the boundary movement to the middle of the strip, the S–N boundary motion equation is obtained for a coplanar waveguide, proceeding in doing this from the motion equation of magnetic flux vortices under certain restrictions specified. Results. The time of S-state destruction has been numerically estimated: 1) for a wide superconducting film of YBa2Cu3O7–d composition, the destruction is by the direct current and 2) for a coplanar waveguide based on the same film, the destruction is by the microwave current. When the superconductivity is small (I / I c ³ 1), the destruction time values in both cases are close to each other within the order of magnitude. Conclusion. It is for the first time that the S-state destruction time in a coplanar waveguide has been expressed in terms of the microwave current distribution in the waveguide. It has been shown that this characteristic linearly depends on the ratio between the critical current and the microwave current amplitude in contrast to a quadratic dependence obtained for a superconducting strip with a direct current.

For installation in the public electric power grid of the city of Augsburg, Germany, a resistive superconducting fault current limiter (SFCL) was designed, constructed, tested and operated in the framework of a partially funded project ‘ASSiST’. Right from the beginning, it was agreed to aim for a prolonged operation even after closure of the project. This endeavor has been started due to a fundamental need to limit the prospective fault currents at a feeder point of the grid and in order to create long-term operational experience on a device seamlessly integrated into commercial grid components and switchgear, thus demonstrating a high level of readiness for widespread application. It revealed that the SFCL was of robust design – withstanding all electrical tests including a special two-phase fault and sustaining stable cryogenic conditions even during partial outages of the cooling system – and that the technology is reducing loss by shunt reactors. Furthermore, due to the control equipment on medium voltage level, valuable insights on grid behavior could be gained. The extended operation for 4 years has clearly shown the performance and robustness of SFCL technology in feeder points on MV level and provides a reference point for further commercialization. [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]

In this paper, operational principles of a cryogenic memory cell that utilizes high-temperature superconductors (high-Tc) are presented. Such a cell consists of three inductively coupled Josephson junctions coupled via inductors. Design and operational logic of this type of cell were recently introduced and demonstrated for low temperature 4 K environment. The basic memory cell operations (read, write, reset) can be implemented on the same simple circuit and both destructive and non-destructive memory cell operations can be realized. Here, we present the design principles and computational validation of basic memory cell operations (write, read, and reset) for the high-Tc memory cell. Our results for the high-Tc memory cell operations show very good resemblance with the previously presented low-temperature 4 K memory cell operations. [ABSTRACT FROM AUTHOR]

We have shown that HTSC ceramic can be synthesized in the chamber of a plasma-chemical reactor. This method makes it possible to significantly reduce the solid phase synthesis process and obtain modified HTSC ceramic with a given content of nonsuperconducting additives that act as pinning centers. [ABSTRACT FROM AUTHOR]

Today, with the high promotion of technology and the expansion of industries, electric motors are used extensively and consume a large part of the electrical energy produced by power plants. Therefore, researchers and experts have always sought solutions to make electric motors with high reliability and low losses. The machines are made of a high temperature superconducting motor with high efficiency are called high temperature superconductor -induction synchronous motor (HTS-ISM). In this paper, the high-temperature superconducting induction/synchronous motor (HTS-ISM) is studied. Optimizing of torque density and the structural dimensions of HTS-ISM is done using one of the newest optimization methods, the collective decision optimization algorithm (CDOA). The results show a torque of about 51.75% increase via the optimization process. Also commonly used optimization method, particle swarm optimization algorithm (PSO) method was implemented to compare the results. The comparison has proved that the CDOA method high capability to optimize the motor design parameters. All of the algorithms in this paper is performed with MATLAB software.

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]

Two fusion reactor designs based on electrostatic plugging of a magnetic cusp system—known as electromagnetic or magnetic electrostatic plasma confinement (MEPC)—are analyzed for feasibility. Both designs use the linear set of ring cusps geometry. The first design, proposed by Dolan (Current trends in international fusion research, Springer, 1997), utilizes low-temperature superconductor technology and is comparable in size to the ITER or DEMO tokamaks, while producing 500–1000 MW th of fusion power. The second design is more compact, assuming more powerful magnetic fields are now conceivable with high-temperature superconductor technology, and produces 50–150 MW th of fusion power. Using scaling equations from Dolan, both reactors have an estimated energy gain Q ≈ 10 when neglecting impurities and alpha heating. A different model of conduction and diffusion losses, including the effect of minor impurities, is developed. This model predicts Q values about 3–5 times smaller than Dolan. Reactor engineering considerations such as the first wall, blanket, and magnetic forces in a linear set of ring cusps geometry are discussed. An experimental program to resolve outstanding questions and verify scaling laws is needed to determine the feasibility of an MEPC fusion reactor. [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]

Two designs have been proposed for segment-fabrication of the high-temperature superconducting (HTS) helical coils in the FFHR-d1 helical fusion reactor, joint-winding of the HTS coils wound by connecting conductor segments, and the ‘remountable’ HTS magnet (here ‘remountable’ means being able to mount and demount repeatedly) assembled from coil segments with demountable joints. A bridge-type mechanical lap joint and mechanical edge joint are planned to be applied to those two designs, respectively. This paper presents the progress in electrical and mechanical performances of the mechanical joints of HTS conductors and methods to evaluate their quality for segment-fabrication of HTS helical coils. R&D of joint performance has progressed during this decade and it shows acceptable performance for the HTS helical coils. The contact-probing current transfer length method and x-ray computer tomography scanning are promising for quality assessment of the joints and HTS tapes. [ABSTRACT FROM AUTHOR]

Recent highly accurate sound velocity measurements reveal a phase transition to a competing phase in YBa2Cu3O6+δ that is not identified in available specific heat measurements. We show that this signature is consistent with the universality class of the loop current-ordered state when the free-energy reduction is similar to the superconducting condensation energy, due to the anomalous fluctuation region of such a transition. We also compare the measured specific heat with some usual types of transitions, which are observed at lower temperatures in some cuprates, and find that the upper limit of the energy reduction due to them is about 1/40th the superconducting condensation energy.

In this paper, we present the experimental results on the modification of the temperature dependences of the thermopower and the Nernst coefficient in a high-temperature superconductor of the Y0.85Ca0.15Ba2Cu3Oy composition under lanthanum and praseodymium doping. We have revealed specific features of the studied impurities influence in comparison with cases of single doping which are resulted from the presence of calcium ions in the lattice. The joint quantitative analysis of the experimental temperature dependences of the transport coefficients was performed, and this allowed us to determine the values of the main energy spectrum and charge-carrier system parameters in the studied samples. We analyzed the reasons for changes in the nature of the lanthanum and praseodymium influence induced by the calcium ions’ presence in the lattice and showed that they were different. The results obtained for the modification of the energy spectrum structure under doping allowed us to explain the peculiarities of the concentration dependences of the critical temperature in the systems under study.

We have studied the possibility of utilizing artificial intelligence (AI) models to optimize high-temperature superconducting (HTS) multilayer structures for applications working in a specific field and temperature range. For this, we propose a new vortex dynamics simulation method that enables unprecedented efficiency in the sampling of training data required by the AI models. The performance of several different types of AI models has been studied, including kernel ridge regression (KRR), gradient-boosted decision tree (GBDT) and neural network. From these, the GBDT based model was observed to be clearly the best fitted for the associated problem. We have demonstrated the use of GBDT for finding optimal multilayer structure at 10 K temperature under 1 T field. The GBDT model predicts that simple doped-undoped bilayer structures, where the vast majority of the film is undoped superconductor, provide the best performance under the given environment. The obtained results coincide well with our previous studies providing further validation for the use of AI in the associated problem. We generally consider the AI models as highly efficient tools for the broad-scale optimization of HTS multilayer structures and suggest them to be used as the foremost method to further push the limits of HTS films for specific applications.

As the demand for eco-friendly energy increases, hydrogen energy and liquid hydrogen storage technologies are being developed as an alternative. Hydrogen has a lower liquefaction point and higher thermal conductivity than nitrogen or neon used in general cryogenic systems. Therefore, the application of hydrogen to cryogenic systems can increase efficiency and stability. This paper describes the design and analysis of a cryogenic cooling system for an electric propulsion system using liquid hydrogen as a refrigerant and energy source. The proposed aviation propulsion system (APS) consists of a hydrogen fuel cell, a battery, a power distribution system, and a motor. For a lab-scale 5 kW superconducting motor using a 2G high-temperature superconducting (HTS) wire, the HTS motor and cooling system were analyzed for electromagnetic and thermal characteristics using a finite element method-based analysis program. The liquid hydrogen-based cooling system consists of a pre-cooling system, a hydrogen liquefaction system, and an HTS coil cooling system. Based on the thermal load analysis results of the HTS coil, the target temperature for hydrogen gas pre-cooling, the number of buffer layers, and the cryo-cooler capacity were selected to minimize the thermal load of the hydrogen liquefaction system. As a result, the hydrogen was stably liquefied, and the temperature of the HTS coil corresponding to the thermal load of the designed lab-scale HTS motor was maintained at 30 K.