Vanadium films were grown on MgO (100) substrates using the magnetron sputtering method by adjusting the depositing time and substrate temperature. The superconducting transition Ta changing from 4.43 K to 2.96 K in two-dimensional (2D) V films can be explained by proximity effect, and the Ta decreases from 3.22 K to 2.65 K as the disorder degree described by Ioffe-Regel constant kFl increases in three-dimensional (3D) V films. Superconductor-metal transition (SMT) occurs in 3D V films that were deposited at different substrate temperatures. In 3D V film deposited at 723 K, the resistivity first decreases abruptly and then becomes nearly independent of temperature due to dissipation effect. While in V film deposited at 623 K, the resistivity exhibits three-step development of superconductivity because of the non-uniformity of the Josephson couplings between islands, the slippages of thermally activation (TA) and macroscopic quantum tunneling (MQT) in the film. The 2D V film is the crossover regime, while the 3D V film is dirty limit.
The development of high-temperature superconducting coated conductors (HTSCCs) hinges on the availability of long-length metallic substrates with highly planarized surfaces-ideally achieved through simple, scalable, and low-cost methods. Solution deposition planarization (SDP) using amorphous Y2O3 has emerged as a promising route to flatten Hastelloy tapes. In this work, a self-designed high-throughput SDP system is implemented to enable efficient double-sided coating of Y2O3 at a lifting speed of up to 90 m/h on 30 mm-wide Hastelloy substrate. The process reduces the root mean square (RMS) surface roughness from 15.65 nm to 1.511 nm over 5 & micro;m & times; 5 & micro;m areas. Subsequent buffer layer deposition demonstrates that the planarized surface supports the formation of biaxially textured MgO layers, satisfying a key requirement for high-performance HTSCCs. These results manifest that the developed SDP system is a viable and scalable solution for surface planarization in HTSCC manufacturing.
Compared with E-core high-temperature superconducting (HTS) transformers, toroidal HTS transformers offer advantages such as a more compact structure and lower leakage flux. However, the operation of HTS transformers is affected by dynamic magnetic fields, which induce AC loss and quench risks. In this study, a finiteelement model of toroidal windings was established to investigate and analyze the effects of winding structural parameters-including circumferential spacing angle, number of pancakes, and axial layering of the HV winding-on magnetic field distribution and AC loss. Simulation results indicate that AC loss in the toroidal structure exhibit a mild linear increase under high magnetic fields; Within the operating current range of 16-24 A, a 1 degrees variation in the circumferential spacing angle leads to an approximately 15% change in pancake AC loss; the toroidal winding has a relatively favorable range of packing density that balances AC loss mitigation with manufacturing complexity; and adopting a layered strategy for the HV winding can increase the minimum overall critical current by approximately 20%. This study provides a theoretical basis for the design and optimization of toroidal HTS transformers.
In this work we introduce the Versatile Isotope-Effect Model (VIEM), a semi-analytical framework designed to describe isotope-effect behavior in strong-coupling hydride superconductors. The model introduces a branch-resolved analytical decomposition of the isotope coefficient within the Allen-Dynes strong-coupling kernel, allowing the contributions of phonon mass scaling, Coulomb screening, and weak non-adiabatic corrections to be treated explicitly. In its predictive screening mode, this model provides a baseline "harmonic" estimate of isotope coefficients based on the Allen-Dynes kernel and branch-resolved mass sensitivity, without introducing additional correction terms. Benchmarking against representative hydride systems-including H3S, YH6, and Th-H-show that the framework captures the observed isotope trends more consistently than conventional analytical approximations such as the Eliashberg-McMillan and Gor'kov-Kresin formulations. The results highlight the central role of phonon-branch redistribution in shaping isotope behavior under pressure. Rather than replacing full numerical Eliashberg calculations, the present framework provides a compact interpretive bridge between microscopic phonon physics and experimentally accessible isotope observables, offering an analytical tool for interpreting isotope trends and screening candidate hydrogen-rich superconductors.
The temperature dependence of the thermopower and other transport properties of FeSe0.7Te03 crystals demonstrate behavior that is typically associated with the vicinity of a quantum critical point. For the compositions studied, the ratio of the Seebeck coefficient to temperature (SIT ) follows log(1IT) over a wide range of temperatures. In this range, in the ordered nematic state, the longitudinal resistivity follows a nearly pure quadratic law. These properties provide experimental evidence for an unusual metallic state in non-magnetic FeSe1-xTex near the nematic endpoint.
The magnetic dipole model is of significant value for predicting the far-field distribution of magnetic targets due to its simplicity and computational efficiency. However, its applicable conditions and accuracy boundaries for High-Temperature Superconducting (HTS) magnets and solenoid coils remain poorly defined and lack a systematic quantitative basis. To address this, this paper introduces a weighted second-order moment based on magnetic moments and derives, from electromagnetic field theory, the dimensional characteristics that minimize the dipole approximation error. By combining high-precision numerical experiments incorporating screening current effects and actual measurements, we systematically investigated the calculation accuracy of the dipole model for the external magnetic field of HTS magnets and its variation with distance. The results indicate that the magnet aspect ratio is the key determinant of model accuracy: when the aspect ratio approaches the theoretical optimal value of 0.866, the model achieves the given error threshold within the shortest characteristic distance. For magnets with general aspect ratios, the calculation error at target points beyond 3 times the characteristic dimension can be controlled within 5%; if the aspect ratio is close to the optimal value, this distance can be shortened to approximately twice this dimension. For high-precision scenarios requiring an error <= 1%, more than 6 times the characteristic dimension is typically required, which can be reduced to about four times this dimension under optimal geometric conditions. Furthermore, for elongated magnets, the mechanism by which the multi-dipole equivalent model improves accuracy is attributed not only to the reduction of sub-unit size but also to the adjustment of the sub-unit aspect ratio closer to the optimal value. This study provides quantitative guidelines and an engineering basis for the rapid calculation of the far-field magnetic distribution of HTS magnets and solenoid coils.
A single-layer model longitudinal-field DC cable with a total length of 660 mm was designed and fabricated using eight 4-mm-wide RE-based coated conductors, and its transport characteristics were evaluated in a subcooled cryogenic vessel. At 77 K, a transport current capacity of 2055 A was obtained, corresponding to a 3.1% increase over the self-field value. Under subcooled liquid nitrogen at 67 K, the current capacity reached 4103 A, corresponding to a 4.2% increase, and a larger enhancement ratio was confirmed at 67 K. In addition, good agreement was obtained between the calculated design values and the experimental results considering the longitudinal magnetic-field dependence of the critical current density of the short coated conductor, demonstrating the effectiveness of the longitudinal-field superconducting power cable even under subcooled conditions.
Gourd-shaped high temperature superconducting (HTS) stacked magnet features a closed-loop excitation structure and enables operation in persistent current mode (PCM), with the advantages of compact structure, stable magnetic field and low operational cost. Since the magnet is stacked with multiple mutually insulated gourd-shaped HTS plates, when one or more of these plates undergo quenching, the other plates remain in the superconducting state, demonstrating superior stability compared with conventional superconducting magnets. This paper focuses on the self-protection and self-healing characteristics of the gourd-shaped HTS magnet, which describe the behaviors of the HTS plates and the overall magnet upon quenching. We analyze the variation in the magnetic field and induced current when a single HTS plate is quenched due to thermal disturbance, and investigate the relationship between magnetic field retention ratio and the number of HTS plates. Experimental measurements and finite element simulations are conducted. The results validate that the gourd-shaped HTS plate has the self-protection characteristic and the gourd-shaped HTS stacked magnet has the self-healing characteristic. Specifically, when quenching occurs in a HTS plate, the current in the quenched HTS plate is transferred to other HTS plates through mutual inductance, thereby protecting the quenched plate from burnout, while the current in the remaining HTS plates increases to mitigate magnetic field attenuation. Consequently, the gourd-shaped HTS stacked magnet maintains safe and stable operation.
To address the complex routing limitations of traditional shipboard degaussing systems, high-temperature superconducting (HTS) magnet arrays have emerged as a highly promising alternative due to their high magnetic field strength and modular potential. This paper systematically investigates the engineering architecture of shipboard HTS array degaussing systems, accomplishing a comprehensive study that spans from theoretical derivation to physical empirical measurement. First, an array design workflow for the degaussing system is established, and a full-process derivation is performed using a virtual ship model. Subsequently, the research focus shifts to physical validation, undertaking the development of superconducting hardware for a small-scale equivalent target. Relying on multi-objective Pareto analysis for system parameter optimization, a compact noinsulation (NI) superconducting degaussing prototype was successfully developed. Testing indicates that the prototype operates stably in the 50 K temperature regime under dual-cryocooler refrigeration. At a full-load current of 60 A, it achieves a central magnetic field strength of 2.0 T and an equivalent magnetic moment of 5300 A & sdot;m2, demonstrating outstanding electromagnetic performance. To verify the practical efficacy of the system, ground-level and UAV-based airborne magnetic survey experiments (at a 100 m altitude) were conducted. Employing a data processing strategy based on differential measurement, environmental interference was effectively mitigated through repeated measurements. The empirical results confirm that the prototype can accurately and stably output the preset magnetic moment, with its far-field distribution aligning highly with theoretical expectations, successfully realizing magnetic field cancellation against the small target. Based on these engineering achievements, this study anticipates the application potential of modular superconducting units in cross-platform deployment, while objectively pointing out that the magnetic shielding effect induced by the high-permeability steel hull must be incorporated into system-level compensation designs in future full-scale ship applications.
The degradation of superconducting properties in Nb/Al-AlOx/Nb Josephson junctions during thermal processing poses a significant challenge for large-scale integrated circuits. In present work, we have successfully developed a fabrication technology with an improved junction structure incorporating a thin aluminum barrier-protective layer (Al*) inserted between the AlOx barrier and the top Nb electrode to enhance thermal stability. A series of junctions with different Al* thickness (0-8 nm) were fabricated, and their electrical characteristics were comprehensively measured at 4.2 K before and after annealing. Among them, junctions with an initial critical current density (J(c0)) of similar to 6 kA/cm & sup2;, an Al* layer thickness of approximately 4 nm yields optimal thermal stability without excessively suppressing J(c0). Experimental results demonstrate that after annealing at 250 degrees C for 30 minutes, the normalized critical current (I-c/I-c0) of the optimized junctions remains at approximately 75%, whereas conventional junctions retain only similar to 40%. This structural modification effectively extends the thermal process window by approximately 25 degrees C, thus significantly improving the compatibility of Nb/Al-AlOx/Nb junctions with advanced semiconductor fabrication processes.
Polycrystalline materials for use in research and industry are often fabricated using powder filling and forming techniques. Since the resulting structures formed through powder-based fabrication depend on particle properties (e.g., size, shape, and ductility), a deeper understanding of the effects of these properties is essential for advancing material development. We focus on the shape anisotropy of particles and its influence on MgB2 materials in this study. Anisotropic particles are obtained by microscopic deformation of ductile Mg that occurs during mechanical mixing. The use of deformed particles with anisotropic shapes positively impacts the mass density of MgB2 materials. The anisotropic particles also tend to align roughly in a preferred direction during material processing under a uniaxial force. This alignment tendency can be utilized to control the void orientation induced by anisotropic particles in polycrystalline materials. These results provide insights into how particle shape anisotropy and ductility affect the material structure formed through powder-based fabrication. The structural findings presented here will be useful in developing various powder-based materials, including polycrystalline MgB2 superconductors.
Precise measurement of large direct current is essential for scientific research and industrial production, with the Cryogenic Current Comparator (CCC) being the most accurate method. However, the high-current application of CCC is restricted due to the quenching of its superconducting shielding and the possible damage of its Superconducting Quantum Interference Device (SQUID). This paper proposes and optimizes a hybrid shielding that combines an external ferromagnetic shielding and an internal folded low-temperature superconducting shielding to overcome these problems. This hybrid shielding can protect the superconducting shielding from quenching and provide a low-interference environment for the magnetic modulator to replace SQUID. Firstly, through finite element analysis, this paper optimizes the folded superconducting shielding to make its shielding effectiveness (SE) reach 96 dB, sufficient for ambient magnetic fields. Then, based on superconducting shielding, external ferromagnetic shielding was introduced, a ferromagnetic shielding with a vertical air gap was selected, and its parameters were optimized. The research results indicate a strong synergistic effect between the two shields. When the external DC magnetic field is 40 mT, the magnetic field at the entrance of the superconducting shielding decreases dramatically from 40 mT to 0.011 mT, while the internal SE increases from 96 dB to 166 dB. At last, anti-interference simulations under practical operating conditions further suggest that the design is largely insensitive to primary busbar eccentricity and can effectively suppress strong external current-carrying conductor interference (flux-based SE > 100 dB). This work provides a foundation for designing high-precision, high-reliability CCCs for large direct current applications.
Flux-reversal permanent magnet electrical machine (FRPMEM) has advantages such as high torque density and high power density, and has broad application prospects in offshore wind power generation. However, the current-carrying capacity of the traditional copper armature winding is limited, making it difficult to further increase the motor's electrical load. This paper proposes a Modular Dewar Multiplexing High-Temperature Superconducting Armature Flux-Reversal Permanent Magnet Electrical Machine (MHTSA-FRPMEM), which uses high-temperature superconducting (HTS) armature windings instead of traditional copper armature windings. This paper details the topology and working principle of the MHTSA-FRPMEM, finding that compared to the conventional HTS armature winding permanent magnet synchronous machine (HTSAW-PMSM), the permanent magnet excitation magnetic field of the MHTSA-FRPMEM has less influence on the HTS armature winding. The winding arrangement of the twelve-phase HTS armature winding is analyzed, and an electromagnetic scheme for a 20MW MHTSA-FRPMEM is designed and its key parameters are optimized. Compared with the conventional HTSAW-PMSM with the same rated power, its torque density can be increased by >40%.
High-temperature superconducting (HTS) motors offer high power density and efficiency and have broad application prospects in the aerospace sector, while transmission losses under high-frequency transport currents limit motor performance and increase cooling system requirements. This study investigates the transmission loss suppression effect of REBCO racetrack coils by fabricating coils with non-filamented and four-filament REBCO tapes, and measuring their losses using the calorimetric method. Furthermore, two-dimensional T-A models were established for coils with 2, 4, 6, 10, and 20 filaments to study the dependence of loss suppression on filament number and transport current frequency. The results indicate that the loss reduction ratio increases with both filament number and transport current. These findings provide critical data for optimizing HTS motor winding structures and operational conditions, and offer a theoretical basis for improving motor efficiency and reducing cooling system load.
This study theoretically analyzed the static and dynamic properties of vortices and antivortices in mesoscopic superconductors submitted to an artificial pinning created by a current-carrying wire oriented perpendicular to the superconductor strip. The equilibrium configuration of vortex-antivortex (v-av) pairs and their motion were obtained using London theory and a Langevin molecular dynamic algorithm. The results indicate that the equilibrium configurations of v-av depend on the value of the applied current of the conducting control strip and the size of the superconducting sample. When subjected to an external dc transport-current, creation, annihilation, movement, entry and exit of v-av pairs from the superconducting sample can be observed, with behavior dependent on the direction of the external current applied to the superconductor. For low values of external currents, the v-av motion does not follow the induced Lorentz force direction, evidencing a vortex-guidance effect and the resulting transverse electrical field.
The superconductor/guideway relationship is similar to the wheel/rail relationship of the highspeed railway, which is of paramount importance in maglev system. In the superconductor/guideway relationship, the levitation and guidance characteristics of high-temperature superconducting (HTS) materials directly impact the dynamics of HTS maglev vehicles. In light of this, this paper investigates the levitation and guidance characteristics of the superconductor/guideway relationship affected by different external factors. First, establish a two-dimensional superconductor/guideway relationship model considering multi field coupling. Second, propose a calculation method considering the interaction between superconductor and guideway to simulate the forced lateral and vertical vibrations as well as the longitudinal motion of dewar. Then, an equivalent three-dimensional mechanical model of superconductor/guideway relationship that takes into account the multi field coupling effects of electricity, magnetism, thermality, and force is established. Finally, focusing on the impacts of dewar’s working height, magnetic field’s irregularity, and HTS bulks’ working temperature, the dynamic characteristics of superconductor/guideway relationship in motion can be studied. This paper employs the mechanical model of equivalent three-dimensional superconductor/guideway relationship established to analyze the impacts of three external factors on levitation and guidance characteristics under multi-field coupling, providing effective references for the dynamic response of HTS bulks’ levitation and guidance characteristics.
In this paper, we successfully achieved a 10-10 Omega level resistance at 4.2 K in a simple soldering joint using commercial REBCO tape with a Cu stabilizer layer. The lowest joint resistance can reach 1.3 & times; 10-10 Omega, which may be low enough for the requirements of gigahertz NMR. Moreover, it is found that the joint resistance is even higher when using the REBCO tape without the Cu stabilizer layer. The micro-CT was introduced to detect the 3D microstructure of the REBCO joint non-destructively. It has been found that the joint from the REBCO tape without Cu stabilizer has significantly more holes in the joint area, which may be due to the lower wetting properties of the Ag surface to the solder than the Cu surface. The more holes mean a smaller effective joint area, which can cause higher joint resistance.
The Meissner effect is the expulsion of magnetic flux from the interior of a bulk superconductor in the presence of the constant critical magnetic field by the persistent current circulating near the surface of the superconductor. The conventional theory of superconductivity explains the appearance of the persistent current in the Meissner effect and other macroscopic quantum phenomena observed in superconductors as a consequence of the quantization of angular momentum of Cooper pairs. According to the alternative theory of hole superconductivity the persistent current appears due to the Lorentz force acting on a radial charge flow rather than due to quantization. Therefore, the author of this theory, Jorge Hirsch, argues in his numerous publications that a radial charge flow is required to explain the Meissner effect. This article draws attention to the fact that the appearance of the persistent current because of quantization is not only the statement of the conventional theory of superconductivity, but first of all the experimental fact that cannot be explained using the Lorentz force. Therefore, the explanation of the Meissner effect does not require radial charge flow.
This study investigated the effect of La doping on the superconducting properties of filamentary Sm1.18Ba2.12-xLaxCu3.09O7-delta samples prepared by a solution spinning method. The La-undoped Sm123 filament partially melted in 3% O2 + Ar showed no superconductivity at 77 K in the self-field. When doped with a small amount of La and partially melted in 3% O2 + Ar, the Sm123 filament became superconductive and its transition temperature (Tc) and Jc(at 77 K in the self-field) exceeded 90 K and 104 A & sdot;cm-2, respectively. The La-doped Sm123 filaments also showed anisotropic Jcbehavior. Although Sm123 doped with x = 0.001 La disappeared its superconductivity under an applied magnetic field of 16 T, Sm123 doped with x = 0.005 La maintained Jc values above 103 A & sdot;cm-2 under applied magnetic fields up to 18 T. Moreover, the filamentary Sm123 sample with x = 0.005 La and treated in 3% O2 + Ar can potentially achieve a high irreversibility field (approximately 35 T) at 77 K.
We report the changes of crystal structure and T-c in the ternary boride Re2-xMxB system (M = V, Mo, and W). The stable structure differed across a concentration range of approximately 0.5 < x < 0.6: with the Mg2Cu-and CuAl2-type structures in the Re-and M-rich regions, respectively. In the V dopant case, we discovered new superconducting phases: Re1.19V0.81B (T-c = 1.4 K), which crystallizes in the CuAl2-type structure, and Re1.66V0.34B (T-c = 3.9 K), which crystallizes in the Mg2Cu-type structure. In the Mo and W dopant cases, we discovered new superconducting phases that crystallize in the Mg2Cu-type structure: Re1.44Mo0.56B (T-c = 4.6 K) and Re1.53W0.47B (T-c = 4.8 K). From the physical property measurements, these new compounds are type-II superconductors that can be recognized within a weak coupling BCS framework. Compared with the known related superconductors, MoReB and WReB, which crystallize in the CuAl2-type structure, the changes of T-c showed opposite trends in the cases M = Mo, W and M = V. The electronic density of states at the Fermi level and the electron-phonon coupling constant were dominant factors for increasing T-c, respectively.
