Earticle

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.

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-δ (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 nextgeneration electric propulsion systems.

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°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.

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.

Accurate measurement of contact resistance in no-insulation (NI) high-temperature superconducting (HTS) coils is crucial for their performance evaluation. The sudden discharge test is a widely used method for measuring the contact resistance of NI HTS coils. However, there are several issues regarding the data acquisition system (DAQ) during the test. In particular, the DAQ must operate at a sampling rate exceeding 500 S/s. An infinite impulse response (IIR) filter can introduce a phase delay into the filtered signal compared to the original data. For instance, applying a 4-Hz low-pass Butterworth filter to a high-frequency signal may lead to measurement errors due to this delay. Moreover, remnant field induced by the screening current after the current transportation introduces uncertainty of conducting sudden discharge tests. This paper proposes the qualified settings of DAQ system configuration for sudden discharge test and suggests an alternative method for measuring the contact resistance of NI HTS coils.

In recent years, the interaction force between a permanent magnet and a closed superconductor coil has been gradually investigated in depth. The principle and application potential of an energy storage/convertor composed of a magnet and a closed superconducting coil have been proved. However, the study on the force between a magnet and a non-closed superconducting coil (superconducting roll stack) has hardly been reported in previous literature. The behavior of this kind of interaction and its influence to the interaction force between a permanent and a closed superconducting coil are also still unclear. In this paper, first we investigated the interaction force between a magnet and a superconducting roll stack. Then, a series of experiments were designed and conducted to clarify the factors affected the interaction force, including the geometrical parameters of the superconducting roll stack and the magnetic field density at the roll stack. Moreover, the comparison of the interaction forces between the magnet and roll stack or a closed coil was also introduced.

This paper presents the magnetic field analysis of the racetrack double pancake field coil for the 10 MW class superconducting wind turbine which is considered to be the next generation of wind turbines using the 3 Dimensional FEM(Finite Elements Method). Generally, the racetrack-shaped field coil which is wound by the second generation(2G) superconducting wire in the longer axial direction is used, because the racetrack-shaped field coil generates the higher magnetic field density at the minimum size and reduces the synchronous reactance. To analysis the performance of the wind turbines, It is important to calculate the distribution of magnetic flux density at the straight parts and both end sections of the racetrack-shaped high temperature superconductivity(HTS) field coil. In addition, Lorentz force acting on the superconducting wire is calculated by the analysis of the magnetic field and it is important that through this way Lorentz force can be used as a parameter in the mechanical analysis which analyzes the mechanical stress on the racetrack-shaped field coil.

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.

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.

The Small Punch Test (SPT) was developed to evaluate the softening and embrittlement of materials such as power plants and nuclear fusion reactors by taking samples in the field. Specimens used in the SPT are very thin and small disk-shaped compared to specimens for general tensile test, and thus have economic advantages in terms of miniaturization and repeatability of the test. The cryogenic SPT can also be miniaturized and has a significantly lower heat capacity than conventional universal test machines. This leads to reduced cooling and warm-up times. In this study, the cryogenic SPT was developed by modifying the existing room temperature SPT to be cooled by liquid nitrogen using a super bellows and a thermal insulation structure. Since the cryogenic SPT was first developed, basic experiments were conducted to verify the effectiveness of it. For the validation, aluminum alloy 6061- T6 specimens were tested for mechanical properties at room and cryogenic temperature. The results of the corrected tensile properties from the SPT experiment results were compared with known room temperature and cryogenic properties. Based on the correction results, the effectiveness of the cryogenic SPT test was confirmed, and the surface fracture characteristics of the material were analyzed using a 3d image scanner. In the future, we plan to conduct property evaluation according to the development of various alloy materials.