Earticle

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.

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.

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.

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.

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 (Je) 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 (σy < 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.

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.