Earticle

It has been over 100 years since Dutch physicist Onnes discovered the phenomenon of superconductivity. About 20 years after the discovery of zero resistance, German physicist Meissner discovered another property of superconductivity, perfect diamagnetism. Zero resistance can bring about revolutionary changes in the transportation and management of electricity, and perfect diamagnetism can be used in magnetic levitation trains, contactless bearings, and magnetic shielding, etc. In 1937, Type II superconductor with high magnetic limits was discovered. The Type II of superconductors led to the industrialization of medical Magnetic resonance image (MRI) and high-magnetic field magnets. In 1960, the tunneling phenomenon, in which electrons move from one conducting layer to the opposite conducting layer through a thin insulating layer in superconductors and semiconductors, was observed and its mechanism was theoretically established by Josephson. Superconducting quantum interference device (SQUID) sensors that utilize the tunneling phenomenon at the Josephson junction are used in a wide range of fields, including medical and geomagnetic detection, and their scope of use is expanding to Quantum computers. In 1986, a high-temperature (Tc) oxide superconductor whose Tc exceeded the superconducting temperature limit of the BSC theory was discovered. Physicists are also making efforts to elucidate the high-temperature superconductivity phenomenon, which is difficult to explain with the BCS theory based on the interaction of phonon vibration and electrons. If a room-temperature superconductor is discovered through exploration on new superconducting materials, the future human life and industry will be innovatively changed by the superconducting technology.

Theoretical calculation of superconducting state parameters (SSPs) like electron-phonon coupling strength ( 𝜆 ), Coulomb pseudopotential (𝜇∗), transition temperature (𝑇𝐶), effective interaction strength (𝑁0𝑉) and isotopic effect parameter (α𝐼) of alkali metals Li and Na have been carried out in the framework of pseudopotential theory. Presently computed SSPs are found to be in good agreement with other reported results. Further, the dependence of SSPs on pressure and hence compressed volume has also been investigated by including the volume dependence of Fermi momentum (𝑘𝐹), Debye temperature (𝜃𝐷) and phonon frequency. It is found that 𝜇∗very feebly depends on compression in volume. The compressed volume at which Coulomb repulsion and attractive electron–phonon interaction are equal is known as critical volume and the corresponding pressure is known as critical pressure. At critical volume, transition temperature and effective interaction strength become zero. It is observed that the results of critical volume predicted by different approaches are in good agreement.

High-entropy alloys (HEAs) consist of five or more principal elements with atomic fraction between 5 % and 35 %, randomly distributed throughout the lattice points. Recently, a simple body-centered cubic structure HEA superconductor, Ta1/6Nb2/6Hf1/6Zr1/6Ti1/6, was discovered and classified as a type-II superconductor with a critical temperature of approximately 8 K. Ta-Nb-Hf-Zr-Ti HEA superconductors exhibit a large critical current density of 1 MA cm-2 and demonstrate robust superconductivity against irradiation-induced disorder. We have synthesized HEA superconductors based on the composition Ta1/6Nb2/6Hf1/6Zr1/6Ti1/6 with various Ce doping concentrations (0.1 wt%, 0.5 wt%, 1 wt%, 2 wt%, 4 wt%, 8 wt%), investigating the effects of Ce addition on the crystal structure and superconductivity. X-ray diffraction and energy dispersive x-ray spectroscopy results indicate the complex Ce addition effects on the crystals. Notably, while the superconducting transition temperature remains largely unaffected by the presence of magnetic impurities, it is found to be closely related to the lattice constant, which changes with varying Ce doping concentrations.

Iron chalcogenides exhibit a variety of emerging properties via substituting the chalcogenide atoms between Te, Se and S. The interplay between temperature, pressure, and composition in iron chalcogenides drives transitions between various phases, e.g., superconducting, magnetic, and structural phases. These phase behaviors are known to result from tuning the bond angle between Fe and chalcogenide atoms in such Fe-Ch compounds. By growing FeTe thin films on substrates via molecular beam epitaxy (MBE), we tune the epitaxial strain imposed on FeTe, and thus manipulate the Fe-Te bond angle. Our transport and angle-resolved photoemission spectroscopy (ARPES) measurements show that such modulation in the FeTe structure effectively modifies the underlying electronic structure, giving rise to various emerging properties different from those of bulk FeTe. We further propose to systematically investigate FeTe thin films to reveal novel phases inaccessible in bulk iron chalcogenides and study the origin of such emergent behaviors.

Various thin film deposition methods such as RCE-DR (Reactive Co-Evaporation by Deposition and Reaction), MOD(Metal Organic Deposition), MOCVD(Metal Organic Chemical Vapor Deposition) and PLD(Pulsed Laser Deposition) have been used to fabricate 2G HTS (Second-Generation High-Temperature Superconducting) tapes. Especially, 2G HTS tapes fabricated by the PLD process show excellent electrical current conduction properties under high magnetic field and have recently become a popular research field worldwide. In this study, we have examined the substrate heating temperature, oxygen partial pressure, and pulsed laser conditions in vacuum, which are essential conditions for manufacturing 2G HTS tapes by pulsed laser process. we have optimized conditions for the continuous deposition of YBCO (YBa2Cu3O7-δ) superconducting layers using the reel-to-reel method on substrates coated with functional layers. The fabricated tapes were evaluated for their characteristics by analyzing biaxial alignment properties using XRD for 2-theta, in-plane texture, and out-of-plane texture and critical current measurement using the Hall-Ic method.

We present a newly developed machine learning based optimized design method for high-temperature superconducting (HTS) magnet. Previous optimization design methods required performing thousands to tens of thousands of magnet characteristic calculations repeatedly to evaluate the objective functions and constraints. If the computation time for analyzing magnet characteristics was long, the design process inevitably became very time-consuming. In this research, we introduce a method that uses machine learning regression techniques to achieve similar design performance while significantly reducing computation time. XGBoost algorithm was trained to create a virtual model capable of predicting the actual characteristics of the magnet. By utilizing this predictive model, which allows for much faster calculations, rather than directly computing the characteristics during the optimization process, the design process was significantly enhanced in terms of efficiency. The proposed design method was applied to the design of a 2 T-class HTS magnet, and it was confirmed that similar results to the previous design could be achieved much more quickly.

This paper proposes a center field compensation system using PID control with auto-tuning to improve the temporal stability of high-temperature superconducting (HTS) magnets. The proposed control system is designed to mitigate magnetic field drift induced by screening currents, as well as fluctuations resulting from power supply ripple in HTS magnets. Various auto-tuning techniques were implemented and evaluated to optimize the controller gains, thereby improving the performance of the field compensation system. A background coil, simulating a HTS coil, and a central magnetic field compensation coil were fabricated, and experiments were carried out to compare the performance of each auto-tuning method based on Settling Time and %Overshoot. Experimental evaluation of the compensation coil demonstrated that the Cohen-Coon tuning method is the most effective for central magnetic field compensation. Current distortions, replicating drift caused by screening currents in HTS magnets and fluctuations from the power supply ripple, were applied to the background coil. Using the proposed method, the central magnetic field was successfully compensated, significantly enhancing the temporal stability of the magnet. After successful validation of the auto-tuning-based central magnetic field compensation technique, a Z0 compensation coil for the 400 MHz (9.4 T) HTS NMR magnet was designed and fabricated. Applying the proposed system to HTS NMR magnets is expected to significantly enhance the temporal stability of the magnetic field.

This research presents a preliminary cost analysis and estimation for superconductor used in superconducting magnetic energy storage (SMES) systems, targeting energy capacities ranging from 1 MJ to 1 GJ, relevant for power grid and industrial applications. Utilizing high-temperature superconductor (HTS) rare-earth barium copper oxide (REBCO) coils in SMES can help compensate for power quality degradation and enhance power stability. However, the high capital costs of SMES remain significant challenges, with costs varying across different energy capacities. First, SMES designs in solenoidal configurations are presented and compared, considering design parameters such as total conductor length, operating current, and magnetic field at the coil center. Then, preliminary cost estimates of these designs are provided based on the price of superconductor. This analysis offers insights into the economic considerations for superconductor in SMES designs and highlights the potential benefits of implementing HTS REBCObased SMES systems across various applications.

In this paper we present design and optimization of shimming coils to correct low-order field gradient components deteriorated by screening currents in high-temperature superconducting (HTS) NMR magnets. The unique geometry of HTS wires induces screening currents, which generate low-order field gradients that degrade the magnetic field quality. To compensate the low-order field gradients, high-strength low-order shimming coils were designed. At first, the target field method was employed to derive the initial shapes of the shimming coils. Subsequently, a genetic algorithm (GA) was utilized to optimize the coil geometries, ensuring ease of fabrication while maintaining high performance. The performance of the optimized coils was validated through virtual field mapping and COMSOL simulations, demonstrating their effectiveness in compensating for targeted gradients with correction efficiencies exceeding 99%. The experimental evaluation will be carried out following the fabrication of the shimming coil in accordance with the proposed design.

Electric motors, as the core of modern electric propulsion platforms, face increasing demands for high power density and lightweight designs. Conventional electric motors, relying on copper windings and iron cores, encounter significant limitations in meeting these requirements, particularly in applications such as aircraft and heavy-duty vehicles. High-temperature superconducting (HTS) tapes, characterized by their superior current-carrying capacity under critical conditions, offer a promising alternative. Motors incorporating HTS tapes demonstrate exceptional power-to-weight ratios, driving extensive research into replacing conventional motors. However, for mobility applications, HTS motors require optimized support structures designed to meet weight constraints. Unlike static applications of HTS coils, the support structure for a rotating superconducting rotor must ensure torque transmission and maintain cryogenic conditions while addressing both structural and thermal factors. This study focuses on the optimized design of the support structure for a superconducting rotor equipped with HTS coils. The proposed design is evaluated through finite element method (FEM) analysis, verifying its mechanical and thermal performance under operational conditions.

Recently, as the sense of crisis over global climate change has grown, the international community is implementing carbon emission regulations and carbon neutrality policies. Efforts to reduce emissions are being strengthened in the transportation and transport sectors, which account for 25% of global greenhouse gas emissions. In response to these regulations and policies, efforts are being made to apply eco-friendly electric propulsion technology to aircraft, ships, and automobiles. Researches are being conducted to improve power density and efficiency by using superconductors that have a high current density compared to the copper wire and whose electrical resistance becomes “0” below the critical condition. Among the electromagnet technologies utilizing the high-temperature superconductors (HTS), the non-insulated (NI) winding technique that removes insulation between winding turns can dramatically improve thermal, electrical, and mechanical stability compared to the existing insulation method. However, technical problems arise due to current leakage, such as magnetic field charging-delay and -loss. Especially, when applying the NI technique to the field coil of a HTS synchronous motor, the output responsiveness may be degraded due to current leakage when the motor speed or load changes. Therefore, in this paper, the dynamic characteristics of a HTS motor were analyzed by changing the contact resistance of the NI field coil, which determine the current leakage. By modeling the d−q equivalent circuit for a HTS motor, the motor speed, torque, field leakage current, and field voltage according to the change in d-axis current were analyzed when controlling the maximum torque operation per unit current.

As environmental concerns become a global issue, wind turbines are gaining attention as a sustainable energy solution. Traditional wind turbines use a mechanical gearbox to transfer energy from the low-speed, high-torque blades to the high-speed, low-torque generator. However, mechanical gearboxes present various challenges due to mechanical contact. To address these issues, considerable research has been conducted on magnetic gears. Since magnetic gears operate without mechanical contact, they offer advantages such as high transmission efficiency and inherent overload protection. Various topologies exist for magnetic gears, and with the introduction of modulating gear topology, torque density has been significantly improved. Many studies are focused on further enhancing torque density, one of which involves the use of superconductors. This paper presents the design of a magnetic gear using REBCO superconducting coil magnets to enhance torque density compared to conventional permanent magnet magnetic gears. The design optimization was conducted using the Non-Dominated Sorting Genetic Algorithm II (NSGAII). The performance was evaluated in terms of torque ripple, torque density, and efficiency. In the magnetic gear applying superconductor, it demonstrates performance with lower torque ripple (0.16%/0.25%), lower losses (229 kW), higher efficiency (96.35%), and higher torque density (1.086 MNm/m³).

This study investigates the sublimation characteristics of carbon dioxide (CO₂) capture across various concentrations using Cryogenic Carbon Capture (CCC) technology and evaluates CO₂ capture effectiveness under different temperatures through practical experimental setups. CCC, which captures CO₂ by cooling mixed gases to cryogenic temperatures and separating CO₂ as solid, is recognized as a promising carbon capture technology. The research used two experimental methods—Closed Type and Continuous Type—across CO₂ concentrations of 10%, 20%, and 30%, observing temperature-based sublimation characteristics for each concentration. Each concentration exhibited unique sublimation behavior under varying temperatures, and continuous gas injection experiments simulated practical applications. The results demonstrate CCC's efficiency, suggesting further research into process design for practical CCC systems.

In order to store liquid hydrogen that has recently drawn attention as an eco-friendly energy source, a vacuum-insulated tank is required. However, even if a vacuum-insulated structure is applied, evaporation occurs due to heat leak by room temperature and it increases the pressure of the tank. In general, the pressure is relieved through a vent for stable storage. This method has problems of economic loss and explosion of flammable hydrogen. Therefore, zero boil-off operation is required to re-liquefy the evaporated gas. Zero boil-off (ZBO) operation in large-capacity storage tank is possible using a gas helium circulation cooling system and a condensation pipe. In this paper, the condensation pipe of a 7m3 ZBO liquid hydrogen storage tank combined with a gas helium circulation cooling system was designed and the simulation of the level change of the storage tank according to the operation condition of the gas helium circulation cooling system was performed using the cryogenic thermal fluid program, Thermal Desktop.

This study aims to design a Small Punch Test (SPT) apparatus for cryogenic environments using conduction cooling. SPT is a non-destructive testing method developed to evaluate material softening and embrittlement in applications such as power plants and fusion reactors. Compared to conventional tensile testing, SPT offers economic advantages in terms of miniaturization and repeatability. However, existing cryogenic SPT rely on liquid helium or evaporated helium gas, which involve high costs and inefficiency. In this study, a cryogenic cooling system utilizing a cryocooler was developed to eliminate the use of liquid helium, along with a rotary sample holder designed to enable testing of multiple specimens in a single cooling cycle. Key design considerations included minimizing external heat intrusion, optimizing thermal management of the load application structure, designing flexible copper connectors suitable for rotation, and applying multilayer insulation (MLI) to reduce radiative heat loads. In particular, the conduction cooling path was optimized to ensure that the specimen temperature could be stably maintained below 20 K, while minimizing displacement in the load application structure and enhancing thermal stability tailored to the characteristics of SPT. The proposed testing apparatus significantly improves cost efficiency and testing productivity compared to existing systems, and it is expected to set a new standard for material property evaluation in cryogenic environments.

Most sub-Kelvin refrigerators have been developed to meet the rigorous demands of scientific inquiry. These advanced cooling devices include sorption-based evaporation cooler, Helium3-Helium4 dilution refrigerators, and adiabatic demagnetization refrigerators (ADRs), each of which utilizes fundamental principles such as evaporation cooling, phase separation, and the magnetocaloric effect. Recently, sub-Kelvin cooling has gained significant attention beyond the realm of pure scientific research, driven by the needs of quantum sensing, communication, and computing technologies. This paper describes an innovative singleshot DR (Dilution Refrigerator) system assisted by ADR as a precooler. Primary objective of this development is to minimize the Helium3 inventory without requiring cryogenic heat exchangers, while optimizing thermodynamic efficiency through careful selection of the temperature ranges for ADR and DR operations. Computer simulations, based on the assumption of thermodynamic equilibrium, demonstrate the straightforward operation of the proposed refrigerator with minimal Helium3 usage under various operating conditions For the prototype DR, initial temperatures for the still and mixing chamber are set at 0.6 K and 0.7 K, with a mixture ratio of 40 % Helium3. The Helium3-Helium4 mixture is obtained through the condensation process facilitated by the continuous adiabatic demagnetization refrigerator (CADR), using GGG (Gadolinium Gallium Garnet) as the magnetic refrigerant. The simulation results could predict the conditions for terminating the DR operation. It is anticipated that the mixing chamber can achieve temperatures below approximately 0.2 K, provided the liquid helium meniscus in the still is maintained and the interface between the concentrated and diluted helium is sustained within the mixing chamber throughout the sorption pumping.