Earticle

The precise characterization of critical current, Ic is fundamental for the design and stable operation of large-scale high-temperature superconducting (HTS) applications, such as fusion magnets and power cables. However, unlike low-temperature superconductors (LTS), HTS materials exhibit complex voltage-current characteristics governed by thermal fluctuations and flux creep, leading to significant measurement uncertainties. This paper provides a comprehensive review of the international standards for Ic measurement, specifically the IEC 61788 series, with a particular focus on the transition from Nb-based conductors to REBCO coated conductors (IEC 61788-26). The theoretical background of the E-J power law model is analyzed and various definition criteria of critical current are evaluated to highlight the engineering implications of criterion dependency. Furthermore, key technical requirements for reproducible data, such as atmospheric pressure correction and current transfer length, are discussed in detail. Finally, this paper addresses the engineering gap between standardized short-sample tests and actual magnet performance, examining critical issues including screening currents, self-field effects, and mechanical stress in large-scale systems.

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.

High-temperature superconductor (HTS) magnets for booster synchrotrons with rapid ramping capability and for use as strong light sources (undulators and wigglers) are emerging as key next-generation technologies that can significantly enhance the performance of particle accelerators. They are vulnerable to rapid environmental changes, which can cause a quench and result in severe damage to the magnets and the entire system. Therefore, it is essential to monitor key physical parameters—such as current, voltage, and temperature—in real time with high speed and precision, enabling early detection of anomalies and prevention of system. In this study, we developed a data acquisition system based on the DT9824 module to replace the discontinued SCXI-1125 module. The proposed system is built based on Python and EPICS, without relying on commercial software, offering high flexibility, user configurability, and suitability for automated measurement environments. We have successfully conducted simultaneous acquisition of 32 channels using eight DT9824 modules, and long-term stability tests are underway.

Rutile RuO2 thin films are known to exhibit strain-induced superconductivity, yet their relatively low critical temperature (~ 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.

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 (Tc), determined from temperature-resistivity measurements, showed a gradual decrease as GFO was added. At low concentrations (≤ 0.2 wt.%) Tc and superconducting transition temperature width (ΔTc) remained close to those of the pure sample, whereas higher concentrations (≥ 0.5 wt.%) led to a pronounced Tc suppression and broadening of ΔTc. 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 (R² = 0.9917), demonstrating robustness. This modeling approach enables pre-operational 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.

In this study, Y1.6Ba2.3Cu2.3Ox (YBCO) bulk superconductors were fabricated using a multiple-seeded melt-growth (MSMG) process. The number of seeds (n) varied from 1 to 6. Magnetic levitation forces at 77 K were measured for the YBCO samples cooled under field-cooled (FC) and zero-field-cooled (ZFC) procedures. The maximum repulsive force (Fmax) of the n = 1 sample under ZFC conditions was 64.7 N. As n increased to 4, 5, and 6, Fmax decreased to 60.9 N, 57.6 N, and 54.3 N, respectively. The reduction in Fmax with increasing n was less than 20% compared to the n=1 sample. In contrast, the Fmax of the YBCO samples measured under FC was lower than that measured under ZFC. Specifically, the Fmax of the n = 1, n = 4, n = 5, and n = 6 samples under FC were 19.9 N, 25.9 N, 23.9 N, and 23.9 N, respectively. Due to the magnetic flux pinning under FC, the attractive forces (22-24 N) were much larger than those (below 5 N) under ZFC. In both cooling conditions, the levitation forces slightly decreased as n increased. Despite the decrease in magnetic levitation forces with increasing n, the process offers the advantage of shorter processing times. Consequently, the MSMG process is considered a cost-effective method for producing large-area YBCO bulk superconductors.

This study presents a dynamic simulation-based evaluation of a large-scale helium compressor test system developed for a 5-ton-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 start-up 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.