Search Results (467)

Reliable in situ temperature monitoring is essential for the safe operation of liquid-nitrogen-cooled superconducting cables, yet conventional electrical sensors are often difficult to scale to multi-point deployment in cryogenic, high-current environments. This work presents a fiber Bragg grating (FBG) sensing solution for in situ temperature monitoring of superconducting cables in liquid nitrogen. An FBG array packaged with a polyimide-coated fiber inside a 3 mm stainless-steel tube is deployed along the cable centerline to provide multi-point temperature measurements of the cable core. The system is validated under liquid-nitrogen immersion with a 2000 A current turn-on/turn-off test, with a 1 Hz update rate and a steady-state temperature fluctuation within ±0.1 °C. Experimental results show a continuous temperature decrease during liquid-nitrogen cooling, followed by a cryogenic plateau, during which a spatially consistent 0.6–0.7 °C current-induced temperature rise is observed across multiple sensing points in the present 2000 A turn-on/turn-off test, followed by recovery after current shutoff. Small-amplitude fluctuations during the plateau are attributed to packaging-dependent thermal coupling between the centerline-deployed sensor and the cable core. These results indicate that the proposed FBG-based approach enables reliable cryogenic thermometry for superconducting cables in liquid nitrogen and provides a practical tool for in situ operational condition assessment. Full article

Recently, CuBa₂Ca₃Cu₄O_10+δ (Cu1234) has garnered significant interest owing to its distinctive triple-high superconducting properties (118K high T_c, combined with high J_c and high H_irr at liquid nitrogen temperature at ambient pressure) and potential for practical applications. The Cu1234 is initially synthesized at high pressures and is stable at a room temperature range but tends to decompose upon heating above 300 °C at ambient. In this study, we investigate the thermal stability of Cu1234 through annealing at various temperatures and oxygen pressures. It is found that Cu1234 starts to decompose at approximately 350 °C, 550 °C, and 600 °C when annealed at 1 bar, 100 bar, and 150 bar oxygen pressure, respectively. Prior to decomposition, however, the superconducting properties remain largely unchanged. The decrease in oxygen occupancy within the BaO layer of the BaCuO_3−δ charge reservoir block is proposed to be the primary cause of the structural instability of Cu1234, while higher oxygen pressures retard oxygen loss from this block. Our result suggests that the decomposition temperature of Cu1234 will further increase with higher oxygen pressure, e.g., possibly to 800 °C at 260 bar if a linear extrapolation is adopted. This study offers important insights for fabricating Cu1234 tapes via the powder-in-tube method. Full article

The increasing demand for electric power in hybrid electric aircraft platforms prompts the development of multi-megawatt generators featuring high specific power, compactness and intrinsic fault tolerance. Air-core machines constitute a promising solution to overcome the magnetic saturation and mass limitations of conventional iron-core designs. This paper presents a comparative electromagnetic design study of two air-core synchronous generator topologies for aircraft applications, namely a permanent magnet machine with a Halbach array rotor and an electrically excited synchronous machine featuring a high-temperature superconducting field winding. Both the generators are designed for identical output and adopt a double three-phase stator winding to enhance safety and redundancy. The Halbach array machine is used as the reference configuration representative of a technologically mature solution, whereas the superconducting generator targets high magnetic loadings by means of the superconducting excitation, to minimize the active volume. The solutions proposed in this paper are developed in the frame of a national (Italian) research project dedicated to the study of stages of multi-megawatt fault-tolerant aircraft generators. Full article

As offshore wind power develops toward larger unit capacities and deeper offshore deployments, its inherent power intermittency poses increasing challenges to system stability and reliable grid integration. To address the issues of large-scale wind power fluctuation and efficient energy utilization, an integrated hydrogen production through offshore superconducting wind power (HPOSWP) system is investigated, which combines high-temperature superconducting (HTS) wind generators with water electrolysis. This paper reviews the operational characteristics of the HPOSWP system under wide power fluctuation conditions, specifically assessing the adaptability of high-power-density HTS wind generators and the feasibility of highly reliable liquid hydrogen (LH₂) circulation cooling technologies from a qualitative perspective. This study provides valuable insights into the application of large-scale HPOSWP systems under fluctuating power conditions and establishes a solid theoretical foundation for subsequent system design and engineering implementation. Full article

As one of the three fundamental modes of heat transfer, thermal radiation has long attracted interest due to its independence from a medium and its strong temperature dependence. In extreme environments such as deep space exploration and cryogenic engineering, thermal radiation often becomes the dominant heat transfer mechanism. Consequently, the radiative properties of materials are crucial for achieving precise thermal control, directly influencing the thermal stability and overall performance of advanced systems, including space probes, cryogenic devices, and superconducting components operating under high-vacuum and low-temperature conditions. This paper provides a systematic review of the physical mechanisms, key factors affecting emissivity, major measurement methods, and technological developments related to material radiative properties at cryogenic temperatures. Particular attention is given to experimental methods and techniques describing material radiative behavior, along with a comparative analysis of the suitability of different measurement techniques for cryogenic applications. Finally, the study highlights the significant practical value of this research for fields such as aerospace, precision electronics, and cryogenic instrumentation, aiming to offer insights for optimizing cryogenic thermal management and guiding the design of novel functional materials. Full article

The temporal stability and reproducibility of qubit parameters are critical for the long-term operation and maintenance of superconducting quantum processors. In this work, we present a comprehensive longitudinal characterization of 27 frequency-tunable transmon qubits spanning over one year across four thermal cycles. Our results establish a distinct hierarchy of stability for superconducting hardware. We find that the intrinsic device parameters determining the qubit frequency and the baseline energy relaxation times ($T_1$) exhibit high robustness against thermal stress, characterized by frequency deviations typically confined within 0.5% and non-degraded coherence baselines. In stark contrast, the environmental variables, specifically the background magnetic flux offsets and the microscopic landscape of two-level system (TLS) defects, undergo a significant stochastic reconfiguration after each cycle. By employing frequency-dependent relaxation spectroscopy and a quantitative metric, the $T_1$ Spectral Topography Fidelity, we demonstrate that thermal cycling acts as a “hard reset” for the local defect environment. This process introduces a level of spectral randomization equivalent to thousands of hours of continuous low-temperature evolution. These findings confirm that while the fabrication quality is preserved, the specific noise realization is statistically distinct for each thermal cycle, necessitating automated recalibration strategies for large-scale quantum systems. Full article

Fusion energy represents humanity’s most promising solution for achieving limitless, carbon-free power. The superconducting Tokamak has emerged as the primary pathway to realize this goal. China’s systematic multi-phase strategy, progressing from the Experimental Advanced Superconducting Tokamak (EAST) to the International Thermonuclear Experimental Reactor (ITER) partnership, and now advancing the China Fusion Engineering Demonstration Reactor (CFEDR), has catalyzed transformative innovations in fusion magnet technology, including the development of high-current-density Cable-in-Conduit Conductors (CICC) using both low-temperature superconductors (LTSs) and high temperature superconductors (HTSs), radiation-resistant ultra-low-resistance joints enabling efficient power transfer, multi-sensor quench detection systems with millisecond-level response for magnet integrity preservation, and cryogenic thermal management via multi-stage heat interception zones. This accumulated expertise in superconducting magnet technologies will accelerate the commercialization of fusion energy. Full article

High-temperature superconducting (HTS) technologies continue to advance as promising solutions for large-capacity rotating electrical machinery. However, the cryogenic architecture required to maintain superconducting states remains a critical design challenge, particularly for performance evaluation systems (PESs). Conventional helium–neon (He–Ne) circulation-based cooling enables stable low-temperature operation and has been experimentally validated in previous PES implementations, but it introduces substantial limitations due to installation complexity, flow-induced instability, and limited adaptability to different coil configurations. To address these constraints, this study proposes a conduction-cooled PES architecture optimized for HTS field coil testing and examines its thermal and structural characteristics through comprehensive design and finite element method (FEM)-based analysis. A multi-stage conduction cooling pathway using a cryocooler, thermal straps, and copper heat plates was designed to achieve uniform temperature distribution and reduce thermal gradients across the HTS winding. Three-dimensional FEM simulations were performed to evaluate the steady-state temperature distribution and heat-transfer characteristics of the proposed conduction-cooled PES under representative thermal load conditions, and the predicted cooling performance was comparatively assessed against the He–Ne cooled PES. The conduction-cooled PES was analyzed by comparing its predicted performance with previously obtained experimental results from the He–Ne cooled PES. The proposed conduction cooling architecture achieved a significant reduction in total heat load, decreasing from 177 W in the He–Ne system to approximately 78 W in the conduction-cooled configuration while also improving thermal efficiency and simplifying system integration. In addition, conduction cooling enhances compatibility with a wider range of HTS coil geometries by eliminating the constraints associated with fluid-based circulation. While the proposed conduction-cooled PES has not yet been physically fabricated, the numerical framework was established based on experimentally confirmed operating conditions of the previously implemented He–Ne-cooled PES, and future work will include fabrication and experimental validation of the conduction-cooled configuration. These findings demonstrate that conduction cooling represents a practical and scalable alternative for next-generation PES platforms and provide essential design guidelines for the development of high-field HTS coils and large-capacity superconducting rotating machines. Full article

A demountable connection is necessary to enable quick and easy replacement of high-temperature superconducting (HTS) tape samples during cryogenic (77 K) testing, particularly when investigating their application in superconducting fault current limiters (SFCLs). Testing HTS tapes for application in SFCLs involves inducing their transition from the superconducting state to the resistive state, which can result in sample damage. The contact resistance of the HTS tape to the current lead depends on the area and on the uniform pressure. Stress distribution in screwed connections with two, four and six screws was analysed using a solid model to compare them and achieve the uniform contact essential for minimising contact resistance in cryogenic conditions. The analysis indicated a solution that provides the most uniform pressure distribution across the HTS tape surface. This solution was utilised in subsequent calculations of thermal shrinkage, and for the determination of the optimal disc spring stack configuration. It is imperative that the compensating disc springs maintain the requisite pressure of the copper block on the tape across the entire operational temperature range (room to cryogenic). Furthermore, the disc springs must provide adequate stroke to compensate for the thermal shrinkage of a copper block and an aluminium clamp. Full article

High-temperature superconducting (HTS) conductor on round core (CORC) cables possess the combined features of high current-carrying capacity, strong mechanical properties, and excellent isotropic flexibility. The current relative research on the electromagnetic properties of straight CORC cables has been exceedingly mature. In high-field magnets, CORC cables are typically bent into coils to meet the compactness requirement. Evaluating the bending characteristics of CORC cables, particularly their post-bending electromagnetic properties, holds great scientific significance. In this paper, CORC cables with different sizes of central formers were fabricated to explore the impacts of the bending process and strain on their transport AC loss characteristics. A mapping method was proposed to couple mechanical and electromagnetic models. Results show that the cable sample with a 4 mm outer diameter of the central former exhibits a superior bending characteristic. The bending process on the transport AC loss of CORC cable lies in the redistribution of the magnetic field, while strain mainly affects AC loss by leading to local critical current (Ic) degradation. CORC cables with small bending diameters require electromagnetic–mechanical-coupling simulation to predict their electromagnetic characteristics accurately. Conclusions drawn from this paper will provide invaluable guidance for the fabrication of bent CORC cables. Full article

Strong electron correlation plays a central role in the high-temperature superconductivity (HTSC) of cuprates. However, to date, research has focused only on its role in spin dynamics and related effects, even though it is becoming increasingly clear that spin alone may not be sufficient to create HTSC. Here, we discuss a possible role of electron correlation in the Bose–Einstein condensation (BEC) of Cooper pairs. Recently, we succeeded in observing dynamic electron correlation via inelastic X-ray scattering through results presented in real space. We discovered that electron correlations are strongly modified in the plasmon, proving that electron dynamics significantly affect electron correlation. Earlier, we found that in ⁴He, the atom–atom distance in the BE condensate is 10% longer than that in the non-condensate. These results suggest the possibility that the reduction in electron-repulsion energy upon BEC is driving T_c to high values. Thus, electron correlation itself could be the origin of the HTSC phenomenon. Full article

To achieve global carbon-neutrality goals, magnetic levitation (maglev) technologies offer a promising pathway toward sustainable, energy-efficient transportation systems. In this study, a comprehensive methodology was developed to analyse and optimise the levitation performance of high-temperature superconducting (HTS) maglev systems. Several permanent magnet guideway (PMG) configurations were compared, and an optimised PMG Halbach array design was identified that enhances flux concentration and significantly improves levitation performance. To accurately model the electromagnetic interaction between the HTS bulk and the external magnetic field, finite element models based on the H-formulation were established in both two dimensions (2D) and three dimensions (3D). An HTS maglev demonstrator was built using YBCO bulks, and an experimental platform was constructed to measure levitation force. While the 2D model offers fast computation, it shows deviations from the measurements due to geometric simplifications, whereas the 3D model predicts levitation forces for the cylindrical bulk with much higher accuracy, with errors remaining below 10%. The strong agreement between experimental measurements and the 3D simulation across the entire force–height cycle confirms that the proposed model reliably reproduces the electromagnetic coupling and resulting levitation forces in HTS maglev systems. The paper provides a practical and systematic reference for the optimal design and experimental validation of HTS bulk-based maglev systems. Full article

REBa₂Cu₃O_7−δ (REBCO) coated conductors are considered a critical material for next-generation high-field superconducting applications owing to their superior superconducting performance at elevated temperatures and under strong magnetic fields. However, rapid degradation of the critical current density ($J_c$) under high-field and high-temperature conditions remains a major limitation for their practical applications. To address this, controlling flux pinning centers has emerged as a crucial strategy to enhance performance. Irradiation techniques, as one of the most commonly employed methods, have attracted considerable attention due to their capability to provide precise control, high reproducibility, and flexibility in tailoring the microstructure. In this review, we focus on the effects of proton, heavy-ion, and neutron irradiation on the microstructure and superconducting properties of REBCO coated conductors. We discuss the underlying mechanisms in terms of defect types and distributions, energy loss processes, flux pinning enhancement, and the evolution of $J_c$ and transition temperature ($T_c$). Furthermore, we compare different irradiation methods, highlighting their advantages and suitability across diverse temperature and magnetic field conditions. The potential of hybrid irradiation strategies for creating multiscale composite pinning landscapes is also examined. Future efforts should aim to synergistically combine different irradiation mechanisms and optimize defect structures to develop REBCO tapes with highly isotropic and stable flux pinning, which is essential for large-scale applications in fusion energy, high-field magnets, and aerospace electric motors. Full article

High-temperature superconducting (HTS) DC power devices operate at cryogenic temperatures to achieve high power density for aviation applications. Ensuring reliable operation requires an optimized insulation system capable of withstanding cryogenic DC stress. In this study, finite element numerical simulations were conducted to investigate the transient behavior of electric fields in HTS cable insulation under DC stress at cryogenic temperatures. The results demonstrate that the transient field distribution is strongly temperature-dependent, leading to prolonged high-field exposure near ground terminations. Strategies to mitigate electric field enhancement are proposed to improve insulation reliability, supported by a comparative evaluation of various insulating materials. The simulation-based insights provide design guidance for developing resilient insulation systems for HTS and other cryogenic DC devices. Full article

Magnetic nanoparticles (MNPs) provide a platform for target detection because of their magnetic responsiveness to alternating magnetic fields (AMFs). We developed a detection method using MNPs modified with tumor-homing peptides (THPs), PL1 and PL3, which selectively bind to protein components enriched in malignant tissues. THP-MNPs were synthesized using maleimide-PEG-NHS linkers and characterized using transmission electron microscopy. Human glioblastoma cancer U87MG and normal tissue-derived HEK293 cells were incubated with THP-MNPs, and the magnetic signals were measured using a high-temperature superconducting quantum interference device (SQUID) magnetometer under an AMF (1.06 kHz). Dark-field microscopy confirmed the preferential binding of THP-MNPs to U87MG cells. In the absence of cells, THP-MNPs exhibited AMF-dependent signal enhancement, which correlated with particle size reduction due to THP release. This increase was completely suppressed in the presence of U87MG cells, indicating a strong THP-mediated interaction. PL3-MNPs exhibited superior discrimination between malignant and non-malignant cells. These results demonstrate that SQUID-based magnetic measurements using THP-MNPs enable rapid and label-free cancer cell detection. Full article