A superconducting fault current limiter (SFCL) is a device designed to protect power systems from excessive fault currents. Superconductors exhibit a phenomenon known as quenching, in which they transition to a resistive state when the current exceeds a critical threshold, thereby enabling rapid fault current limitation. LS ELECTRIC, in collaboration with KEPCO, developed a 22.9 kV / 2.0 kA resistive superconducting fault current limiter (R-SFCL) and installed it at the Seogochang Substation for commissioning. Before integration into an actual power distribution system, a low-voltage load test was conducted to verify that the temperature of the liquid nitrogen inside the SFCL remained stable under various thermal load conditions. The load current profiles were established on the basis of seasonal and daily electricity consumption patterns in Korea and also included extreme scenarios involving abrupt load increases.
Superconducting quantum devices based on Josephson junctions have evolved from highly sensitive magnetic sensors to one of the leading platforms for quantum information processing. Early developments of superconducting quantum interference devices (SQUIDs) enabled femtotesla-level magnetic field detection, which led to applications in biomagnetic measurements such as magnetoencephalography and magnetocardiography. These technologies were further extended to ultra-low-field nuclear magnetic resonance (ULF-NMR) systems, where SQUID sensors allow detection of nuclear spin signals in microtesla magnetic fields. Meanwhile, the nonlinear dynamics of Josephson junction circuits enabled the realization of artificial atoms and superconducting qubits. The development of the transmon qubit and circuit quantum electrodynamics architecture significantly improved coherence times and control fidelity, enabling the construction of multi-qubit superconducting quantum processors. This review summarizes the physical principles, technological developments, and system-level implementations of superconducting quantum devices, from SQUID-based sensing technologies to modern superconducting quantum computing platforms.
In this study, a high-precision isolated data acquisition (DAQ) system is designed for stable measurement of low-level voltages under high voltage common-mode environments. The proposed DAQ system is designed to employ a 24-bit Sigma-Delta analog-to-digital converter, a sampling rate exceeding 1 kS/s, measurement accuracy of approximately +/- 0.01%, a common-mode rejection ratio (CMRR) exceeding 130 dB, and channel-to-channel isolation of +/- 500 V-rms. Notably, the importance of channel-to-channel isolation is experimentally verified. The results demonstrate that the absence of isolation can result in spurious voltage signals in both the specific DAQ system and other systems connected to the same measurement environments. A hybrid filtering structure is adopted to simultaneously acquire raw and filtered signals. During measurement, filtered data is used for real-time monitoring, while the stored raw data is post-processed to obtain distortion-free data. Theoretical analysis of infinite impulse response (IIR) and zero-phase filters indicate that IIR filtering causes nonlinear phase response and frequency-dependent group delay, leading to signal distortion, whereas zero-phase filtering eliminates such distortion. Based on the analysis, a post-processing-based zero-phase filtering approach is adopted. The proposed DAQ system is applicable to high temperature superconducting (HTS) magnet quench detection, cell level voltage monitoring in electric vehicle (EV) battery packs, and other high-reliability power and energy systems requiring precise low-level voltage measurements.
The distillation column is a key piece of equipment for obtaining high-purity xenon (purity >= 99.9999%). This study is focused on analyzing the dynamic relationship between pressure and impurity concentration in order to construct predictive models, optimize the operational parameters of the column, and enhance the efficiency of separation. During the research, continuous monitoring of the column pressure and data collection on impurity concentration were conducted. To address data discontinuity, time intervals of less than 1200 minutes with more than three concentration measurement points were selected. Based on the filtered data, a segmented model describing two operating modes of the column was developed. For the dynamic pressure mode, a significant polynomial linear relationship was identified between the fluctuations in impurity concentration and the absolute value of the pressure change rate. During the stable pressure period, an exponential decay model was constructed to describe the dynamics of impurity concentration reduction. The model allows for predicting the time required to achieve the target impurity concentration and the degree of product purity within the expected stable operating time interval of the column. This contributes to optimizing the equipment's operational parameters, reducing energy consumption, and improving the efficiency of gas mixture separation.
This study presents a dynamic simulation-based evaluation of a large-scale helium compressor test system developed for a 5ton-per-day (TPD) hydrogen liquefaction plant. A one-dimensional transient simulation tool, EcosimPro, equipped with the CryoLib library was used to model the thermofluid behavior of the helium circulation loop and investigate start-up and pressure-control strategies relevant to helium refrigeration systems in cryogenic processes. The analysis focused on the coordinated operation of three pressure control valves-PCV501, PCV504, and PCV505-that regulate the suction and discharge pressures of the compressor. Through a series of dynamic simulations, appropriate control logic for stable pressurization and pressure regulation was derived. Sensitivity analysis further revealed that an initial loop pressure between 7 and 10 barA yields the most stable startup condition. These findings demonstrate the usefulness of dynamic modeling using EcosimPro-CryoLib for optimizing control strategies in helium-based thermofluidic systems and provide valuable guidance and reference data for the future operation of hydrogen liquefaction infrastructure.
Deposition process of magnetic particles on two filters during high gradient magnetic separation has been investigated through in-situ optical observation. The deposition process was observed from two perpendicular directions using CCD cameras. In case of relatively high concentration suspension, due to their particle-particle interactions, particles formed the chain or the bundle structures in the flow path before reaching the filters. Such chains and bundles tend to be deposited on the first filter and the spike like structure was formed at the upper stream side of the first filter. On the other hand, particles deposited uniformly on the second filter. These observation results show that it is required to take into account properly the effect of the deposited particles in the sense of the magnetic field distribution and also of the physical obstructions to understand separation performance precisely.
In this work, the effects of GdFeO3 (GFO) addition on the superconducting properties of GdBa2Cu3O7-x (GdBCO) bulk samples were investigated. A series of GdBCO + GFO composites (0- 1.0 wt.%) were synthesized using the solid-state reaction (SSR) method. XRD analyses revealed peak shifts to low angles and increases in the c-axis lattice constant with increasing GFO content. The superconducting transition temperature (T-c), A determined from temperature-resistivity measurements, showed a gradual decrease as GFO was added. At low concentrations A(<= 0.2 wt.%) T(c )and superconducting transition temperature width A(triangle T-c) remained close to those of the pure sample, whereas higher concentrations A(>= 0.5 wt.%) led to a pronounced T(c )suppression and broadening of triangle T-c. Excess conductivity analysis further indicated that the 3D fluctuation region diminished with increasing GFO concentration, suggesting that GFO incorporation weakens interlayer coupling in the GdBCO system.
Accurate prediction of breakdown voltage (BDV) in cryogenic environments is critical for ensuring the operational safety and reliability of high-temperature superconducting (HTS) systems. In such systems, dielectric failure due to extreme thermal and electrical stresses can lead to catastrophic malfunction. This study presents a second-order polynomial regression model that quantitatively predicts BDV in liquid nitrogen (LN2) as a function of electrode gap and diameter. The model was developed based on experimentally measured data and incorporates nonlinear and interaction effects between geometric variables. Statistical validation confirmed its high predictive accuracy (R-2 = 0.9917), demonstrating robustness. This modeling approach enables preoperational insulation design optimization and may be embedded into digital twin frameworks for real-time diagnostics. The findings offer both theoretical insights and practical tools for the development and deployment of next-generation cryogenic insulation systems in HTS applications.
Rutile RuO2 thin films are known to exhibit strain-induced superconductivity, yet their relatively low critical temperature (similar to 1-2 K) limits comprehensive study. Since superconductors in the 2D limit often behave distinctly from the bulk state, it might be important to characterize monolayer RuO2 for understanding dimensionality effects on the strain-induced superconductivity. In this report, we investigated the electronic band structure of the monolayer RuO2 by fabricating a charging-free RuO2-TiO2 heterostructure via pulsed laser deposition (PLD) and performing in-situ angle-resolved photoemission spectroscopy (ARPES). We successfully resolved the electronic band structure of atomically thin RuO2 films and observed a Fermi edge for the monolayer, providing direct spectroscopic evidence that monolayer RuO2 retains its metallicity under coherent epitaxial strain. Our findings provide an experimental basis for investigating superconductivity in the two-dimensional limit and offer a platform to examine strain effects in monolayer oxide systems.
As global environmental regulations intensify, the electrification of the mobility industry is accelerating, thereby increasing the demand for high-power electric propulsion systems. Among the various candidates for application, superconducting motors have attracted considerable attention owing to their potential for delivering exceptionally high-power density. In this study, we fabricated two types of GdBa2Cu3O7-delta (GdBCO) superconducting magnets and evaluated their trapped field performance using a 14T superconducting magnetization system. A single grain bulk magnet, grown by the top seeded melt growth (TSMG) method, exhibited a trapped field of 1.93T at 20K. The stacked tapes, fabricated by commercial GdBCO tapes, showed a maximum trapped field of 1.25T at 20K. While the single grain bulk magnet has an advantage in trapped field performance, the stacked tapes offer benefits in terms of simple manufacturing processes and shape flexibility. These results suggest that simultaneous improvement of trapped field performance and motor design optimization could establish superconducting motors as a core technology for next-generation electric propulsion systems.
In 2013, highly concentrated rare-earth-rich mud (REE-rich mud) was discovered around Minami-Torishima Island, presenting an opportunity to develop a new source of rare-earth elements (REEs). This study proposes a new method for selectively removing non-REE components using magnetic separation. First, we calculated the theoretical levitation positions of the target minerals using the magneto-Archimedes method, considering the mineral density, magnetic susceptibility, and magnetic field distribution of a high-temperature superconducting (HTS) bulk magnet. Next, we conducted separation experiments to selectively isolate REEadsorbed apatite from a simulated mud sample consisting of a mixture of apatite, montmorillonite, quartz, and zeolite. The results demonstrated that non-apatite minerals were successfully removed using magnetic levitation method. Based on these results, we applied the method to actual core samples (REE-rich mud) from the coast of Minami-Torishima Island. These experiments showed that phillipsite could be selectively separated from the core sample using magnetic levitation. However, the overall weight reduction was less significant than that achieved with the simulated REE-rich mud. This discrepancy was attributed to the inability to separate the paramagnetic mineral montmorillonite into the levitated fraction, because of its swelling property and cation exchange capacity, and location-dependent variability in the mineral composition of the core samples. Possible solutions to this problem include improving the sample dispersion and combining this method with other separation techniques.
Engineering correlations are derived to estimate the friction factor and Nusselt number of rectangular helical flow in stacks-inconduit conductors (SICC). AThe SICCs are under current development at KFE (Korea Institute of Fusion Energy) towards the realization of HTS (high-temperature superconductor) fusion system. A copper band is helically wound around the outer wall of a rectangular bundle of stacked REBCO (rare-earth barium copper oxide) tapes, and the space between the bundle and the external jacket serves as a cooling channel for helium gas flow. Key geometric parameters are identified for the SICC structure, and threedimensional numerical analyses are performed with ANSYS FLUENT and real thermo-physical properties of materials and fluids at 20-30 K. The analysis domain consists of (1) the REBCO bundle, (2) the copper band, and (3) the helium gas flow. A special attention is paid to the role of helix angle of copper band (and helium flow), significantly affecting not only the hydraulic diameter and flow length of cooling channel, but also the flow pattern of cooling gas established by the centrifugal force in curved flow passage. The thermo-hydraulic data are simplified with the typical method of dimensional analysis, and it is successfully verified that the dimensionless friction factor and Nusselt number can be expressed in terms of well-known Dean number (composed of inertial, centrifugal, and viscous forces), in a similar way with the helical tube flow. The derived correlations are directly applicable to the ongoing design and manufacturing of SICC, and eventually to the development of forced-flow gas-cooled HTS magnets.
This study explores the enhancement of magnetic field homogeneity in Nuclear Magnetic Resonance (NMR) magnets through optimized ferromagnetic shimming design. Traditional shimming techniques, which involve attaching ferromagnetic materials to the magnet bore, often lack manufacturability considerations, limiting their effectiveness in real-world applications. To address this, we employ a topology optimization (TO) approach using the Solid Isotropic Material with Penalization (SIMP) scheme for design parametrization. The proposed optimization framework includes volume and perimeter constraints to improve the practical manufacturability of the shim. Numerical analysis demonstrates that the TO-based design method achieves superior magnetic field homogeneity, achieving 0.45 ppm with integer thickness shims, compared to conventional designs. This approach also effectively reduces manufacturing complexity by minimizing design sensitivity to the thickness and placement of individual shimming elements. The proposed design framework is broadly applicable to superconducting magnets in NMR and MRI systems, where high magnetic field homogeneity is essential. This study presents a significant advancement in ferromagnetic shimming technology, offering a viable solution for enhancing the performance and manufacturability of high-precision magnetic field devices.
The superconducting accelerator's liquid or superfluid helium cryogenic system requires numerous temperature sensors to precisely monitor key components and ensure the device's safe and stable operation. Uncalibrated temperature sensors are widely used in large scientific facilities owing to their low cost and short supply cycles. This study developed a temperature sensor calibration system suitable for the superfluid helium temperature region. This system combines the comparison method and dynamic calibration while optimizing the calibration approach for different temperature ranges. A total of 20 uncalibrated temperature sensors were calibrated over a temperature range of 300 K to 2 K. Experimental results show that the system can simultaneously calibrate numerous temperature sensors, significantly improving calibration efficiency. In the 4.2 K-2 K temperature region, the calibration accuracy is +/- 6.035 mK, which meets the engineering application requirements of large scientific facilities.
High-temperature superconductors (HTS), owing to their high critical current and critical magnetic field, are utilized in various superconducting applications such as superconducting power cables and high-field magnets. However, REBCO (Rare Earth Barium Copper Oxide) tapes face significant challenges in long-length fabrication compared to low-temperature superconducting wires. Consequently, joining REBCO tapes is essential for their application in superconducting devices. The most widely used method for joining REBCO tapes is mechanical pressure soldering, which inevitably introduces contact resistance at the joint interface. Since superconducting devices operate in cryogenic environments where maintaining minimal losses is critical, minimizing joint resistance is essential. In this study, we evaluated the effect of heating temperature on joint resistance in the mechanical pressure soldering process by selecting four types of solders (Pb37Sn63, In52Sn48, Sn42Bi57Ag1, and In66.3Bi33.7). Lap joint samples were prepared by increasing the heating temperature in 10 degrees C increments above the melting points of each solder, and the surface resistance of each sample was measured. The results were analyzed to identify the appropriate heating temperature.
Heat exchangers are the most effective devices for transferring heat energy in cryogenic fluid equipment. In a cryogenic thermodynamic venting system, the heat exchanger is immersed in a cryogenic liquid and operated to facilitate the heat exchange between the fluids within the heat exchanger. In this unique environment, heat is continuously introduced into the heat exchanger from the external surroundings. This study aimed to numerically investigate the impact of an external heat load on the performance of a heat exchanger. This study assessed the changes in the effectiveness of the heat exchanger when exposed to an external heat load. Specifically, the influence of a linear and constant external heat load along the length of the heat exchanger on its efficiency was analyzed. In addition, this study examined the effect of the external heat load on the effectiveness of a plate-type counterflow heat exchanger. The research findings indicated that the external heat load had a lesser impact on effectiveness reduction when it entered the heat exchanger as a cold fluid rather than a hot fluid. In addition, the decrease in effectiveness was less pronounced when the external heat load was concentrated in the high-temperature region as opposed to a uniform amount of external heat load entering the heat exchanger along its length. The effect of the external heat load based on the number of plates in a plate heat exchanger showed no correlation.
Bi-2212 (Bi2Sr2CaCu2O8+x) high temperature superconducting (HTS) wires are attracting significant attention in high field magnet applications due to their high engineering critical current density (J(e)) and excellent performance in high magnetic fields. However, the Ag/AgMg alloy matrix used in Bi-2212 wires exhibits a low elastic modulus (E = 70 GPa) and yield strength (sigma(y) < 100 MPa) [1], making the wires prone to deformation even under small loads, which leads to performance degradation. These low electromechanical properties impose strain-induced limitations on the performance of high-field solenoid magnets rather than current-induced limitations. To address this issue, enhancing the mechanical strength of Bi-2212 wires is essential. In this study, we aimed to improve the mechanical strength of Bi-2212 wires using a strip lamination technique. The Bi-2212 round wire was processed into a tape form through a flat-rolling process, and Inconel X-750 strips were bonded to both sides of the Bi-2212 tape using a bonding process, resulting in the fabrication of a final Inconel X-750 laminated sample with a thickness of 0.84 mm and a width of 1.88 mm. Tensile tests at cryogenic temperatures (77 K) revealed that the Inconel X-750 laminated sample achieved a strength of 278 MPa at a strain of 0.4 %, representing a twofold improvement compared to the original round wire. Additional investigations included filament area uniformity and Je property changes during the flat-rolling process, as well as interfacial analysis between the Bi-2212 tape and the Inconel X-750 strip during the heat treatment process.
We investigated the flux pinning properties of GdBa2Cu3O7-x (GdBCO) superconducting films grown on a LaFeO3 (LFO) buffer layer forming a bilayer structure. LFO films with different thicknesses and GdBCO thin films were all prepared by using a pulsed laser deposition technique. The magnetization measurements revealed that the critical current density of the GdBCO bilayer structure with the LFO buffer layer increased in low magnetic field regions compared to pure GdBCO films. Notably, the variation in critical current density and the position of the maximum pinning force density did not exhibit a simple dependence on the LFO buffer layer thickness. Dew-Hughes' model fitting confirmed that normal surface pinning is the primary pinning mechanism for both the thinnest and the thickest LFO films. However, for intermediate LFO buffer layer thickness, additional pinning mechanisms beyond normal surface pinning were identified, likely due to the defects from misoriented crystallites, as indicated by the close correlation between the fitting exponent and the grain size of the bilayer structure.
High Jc Nb3Sn wires, which require a high critical current density (Jc), are essential for advanced applications such as fusion energy systems and accelerators. However, achieving thermal stability to prevent premature quench remains a significant challenge in their development. Previous Distributed Tin (DT) Nb3Sn wires use a bronze matrix (Sn 8-12 at%) with low thermal conductivity, which limits heat transfer in Nb3Sn wire, thereby increasing the possibility of premature quench. To address this issue, Kiswire Advanced Technology (KAT) developed Distributed Barrier Strand (DBS) Nb3Sn wires with enhanced thermal transfer. These wires feature individual Nb barriers surrounding each sub-element and copper channels between sub-elements, allowing rapid heat transfer to the exterior and reducing quench risks. This paper presents the results of a study on the diffusion behavior and electrical property changes of High Jc Nb3Sn DBS wires under various heat treatment schedules. Additionally, optimal heat treatment conditions that enhance Jc characteristics without premature quench were discussed, and EDX analysis results for each heat treatment condition are discussed.
When studying the properties of the high-temperature superconductor La2-xSrxCuO4 (LSCO), it is crucial to explore the superconducting phase, and the complex intertwined electronic structural phases. These materials are influenced by the degree of impurities and disorders. Growth methods such as molecular beam epitaxy (MBE) or pulsed laser deposition (PLD) possibly play important roles in reducing impurities or disorders. However, optical measurements including Raman spectroscopy has been limited to study thin film grown by MBE and PLD despite its wide applicability in strongly correlated materials. In this study, we utilized optimally doped LSCO (x=0.15) thin films grown by PLD to conduct electronic Raman scattering. Comparing these results with bulk LSCO (x=0.15), we observed clear differences from that of bulk samples. The phonon near 225 cm(-1) in the B1g Raman spectrum did not split and appeared as a single peak, and the two-magnon emerged in an energy range that had not been previously reported. These results indicate better crystal quality of PLD grown LSCO (x=0.15) which shows possible Two-magnon.
