Physica C-superconductivity and Its Applications最新文献

The structural, electrical and magnetic properties of a series of La_3-xSr_xNi₂O_7-δ polycrystalline samples have been systematically investigated with and without high-pressure oxygen annealing. Without annealing, the introduction of Sr at La site leads to a moderate enhancement of conductivity. The high-pressure oxygen annealing leads to an increase of oxygen content by ∼1.08 %. Consequently, the conductivity of the annealing samples is significantly enhanced comparing to the untreated samples. The La_3-xSr_xNi₂O_7-δ samples exhibit metal-like behavior in the whole temperature range with annealing, which is due to the hole doping effect. The present results could contribute to the exploration of possible ambient superconductivity in La₃Ni₂O_7-δ system.

In this paper we examine the mechanisms leading to thermomagnetic instability in nanostructured materials and study their regularities. The appearance of thermomagnetic instabilities in the superconducting state of various materials remains one of the problems of applications of superconductors. We studied the temperature and the magnetic field dependences of the magnetization m(T, H) and heat capacity C(T, H) of a nanocomposite consisting of interconnected lead filaments embedded in nanoporous glass (Pb-PG) with filament diameter d = 7 nm. Porous glass contains an arbitrarily orientated multiply connected system of pores of approximately the same size; lead in the nanocomposite forms a replica of the pore system. Thermomagnetic instability was previously observed in this material in superconducting state at T ≤ 5 K on m(H) dependencies in magnetization studies. We established that high enough external heater power P used during the heat capacity measurements in external magnetic field C(H) at T ≤ 5 K can initiate thermomagnetic instability and penetration of magnetic flux into the nanocomposite. The thermomagnetic instability is generally preceded by a sequence of small heat release events with the same magnitude as P. Another sequence of small heat release events is observed in the region close to H_c2. These events are presumably linked to the thermomagnetic instability process and are caused by small redistribution of magnetic flux in the nanocomposite.

It has been claimed that measurements of trapped magnetic flux in hydrides under pressure provide evidence for superconductivity in these materials (Minkov et al., 2022; Minkov et al., 2023). In recent work we have questioned that claim (Hirsch and Marsiglio, 2022). Here we point out that recent experiments (Bud’ko et al., 2023) provide further evidence supporting our questioning of that claim. We also present calculations for a thin disk and compare these with those previously calculated for a long cylinder. The results are qualitatively similar, and therefore reinforce our previous conclusions. We also address recent criticism of our paper Ref. (Hirsch and Marsiglio, 2022) by Bud’ko (2024) and by Talantsev et al. (2023).

In this study, the influence of conformal pinning centers on enhancing the critical current density in superconductors has been investigated. To increase the critical current density, a square-pinned array with dimensions of 10λ by 10λ under two appropriate conformal transformations is considered. Initially, by specifying the forces acting on the vortices, the relevant Langevin equation for the vortices is solved. By solving this equation, the vortex positions versus time are determined, and using this information, the critical current density is calculated as a function of the magnetic field. Then, the critical current density is calculated for various conformal function parameters in a superconductor tape. The results indicate that after applying two conformal transformations with appropriate parameters, the critical current density could be increased at higher magnetic fields. Simulations demonstrate a 25% increase in critical current density in the optimal case.

Due to the existence of earth magnetic field, it is difficult to detect weak magnetic field from some parts of the body like heart, muscle, nerve and so on. In addition to the requirement for high-sensitivity magnetic field sensors, it is also essential to take certain measures to suppress noise. The axial gradiometer based on low-Tc Superconducting QUantum Interference Device (SQUID) can achieve a noise suppression ratio of 30 dB through the spatial gradient difference of the magnetic field, but the calibration of the magnetic field-to-voltage coefficient (B-V coefficient) generally requires a magnetically shielded room (MSR), which is complex and costly. With finite element simulation and practical experiments, a calibration method for B-V coefficient of the axial hardware gradiometer without shielding was presented in this paper. That is, a larger calibration field was generated for coefficient evaluation in an unshielded environment. At the same time, when the test signal was far away, the spatial gradient difference was used to improve the authenticity of the evaluation results. Through simulation and experimental verification, for the same performance and configuration of the gradiometer, the calibration result was 1.6 nT/V with 0.1 nT/V difference from that in a shielding room. The results showed that the unshielded evaluation method proposed in this paper was practical and could be used to evaluate the B-V coefficient of gradiometer.

The intra-layer no-insulation (LNI) layer-wound REBCO coil has been widely studied for its excellent high thermal stability in the research of nuclear magnetic resonance superconducting magnets. Due to the complex structure of the LNI layer-wound coil and the numerous factors that affect thermal stability, its quench characteristics are not clear. In this paper, a numerical multiphysics coupling model is established to study the transient electromagnetic and thermal behaviors of the LNI layer-wound coil during quench. The results indicate that temperature follows the diffusion law, while the currents evolve through electrical connection and electromagnetic induction. Due to the high contact resistance, the azimuthal current and axial current vary almost in units of the entire coil layer. The direction of the radial current upstream of the turn where a quench occurs is positive due to the bypassing behavior, while the radial current direction is negative downstream. The insulation material inside the LNI layer-wound coil strongly affects the quench propagation. When its thickness decreases, the equivalent radial thermal conductivity increases, thereby increasing the quench propagation velocity and current peak, and shortening the duration of the current response during quench.

High-field magnets have been developed for a broad range of research applications. High-temperature superconducting magnets have received considerable attention due to their potential use in high-field applications. The High Magnetic Field Laboratory of the Chinese Academy of Sciences (CHMFL) is currently designing and constructing high-temperature superconducting (HTS) magnets which need the cooling capacity about 5 W to 10 W at 4.5 K in order to ensure the stability of the system. To meet their operational requirements, a miniature cryogenic system based on the Gifford-McMahon/Joule-Thomson (G-M/J-T) cryocooler has been designed and analyzed. In this research, the performance of the cryogenic system for HTS magnets is investigated systematically by employing both energy analysis and entropy analysis techniques. The results highlight the importance of several key factors, including high pressures, precooling temperature at cooling stages, and J-T exchanger efficiency, for improving the cooling capacity of the cryogenic system. Lowering the precooling temperature can enhance the system cooling capacity and also cause an increase in the precooling capacity. As the pressure increases, the cooling capacity of the system reaches its maximum point at 11.31 bar The J-T heat exchanger accounts for the largest exergy loss rate, 35.2–43.7%. The findings provide technical guidelines for the subsequent experiments and performance optimization of cryogenic system.

With the expansion of distributed power systems and renewable energy worldwide, the use of synchronous condensers (SC) has been gradually increasing to maintain the power quality of an electric grid. Because SC generates fewer harmonics and has the advantage of strengthening system inertia, it is considered as a primary option in Korea over other options such as Static Var Compensator (SVC) and STATic synchronous COMpensator (STATCOM). If superconductor synchronous condenser (SSC) is applied instead of SC, it brings more advantages: (1) it can minimize the adverse impact on the power system due to lower synchronous reactance, and (2) the higher power density can lead to many advantages in a limited area of substation. With these backgrounds, we report a design study on 40 MVAr SSC with no-insulation high-temperature superconductor (NI-HTS) field coil. Firstly, design criteria and procedures for electromagnetic design were set. Secondly, with the design procedure, the electromagnetic design having the minimum HTS conductor usage was obtained among the designs satisfying design criteria. Based on the final design, key characteristics of SSC including no-load voltage, the maximum flux density under the rated-load condition, V-curve characteristic, synchronous reactance, zero sequence reactance, negative sequence reactance, critical current, and NI-HTS characteristics were calculated by using finite element method. Lastly, the design comparison between SSC and SC was presented.

The huge transverse Lorentz force experienced by CORC cable during the operation of fusion projects may cause irreversible degradation of its current-carrying capacity. Therefore, it is particularly important to study the influence of cable parameters on their transverse compression performance, and use these influence laws to adjust cable parameters to improve the critical value of transverse compression load that CORC cables can withstand. Solid copper bar former CORC cables with a former diameter of 5.57 mm are produced using HTS (high temperature superconducting) tapes (manufactured by Shanghai Superconductor) of 4 mm and 5 mm width respectively. The experimental results show that the CORC cable wound with 5 mm wide HTS tape has a greater critical transverse compression load than the cable wound with 4 mm wide HTS tape. This indicates that using wider HTS tapes to wind CORC cables can effectively improve their transverse compression performance. A solid copper bar former CORC cable and a stainless steel spiral tube former CORC cable are also produced. Through transverse compression experiments, it is found that the critical transverse compression load of the solid copper bar former and the stainless steel spiral tube former CORC cable are 130 kN/m and 89 kN/m, respectively. This indicates that the solid copper bar former CORC cable has better transverse compression performance. In addition, we also compared the influences of flat and arc pressure blocks on the transverse compression performance of CORC cables, and this experimental results provided a basis for the selection of the bobbin structure when using CORC cables to make coils.

The high-speed rotating superconducting rotor can be made into a high-precision inertial device. Centrifugal deformation is one of the key factors affecting the drift speed of the rotating superconducting rotor's polar axis. The larger the drift speed, the worse the accuracy of the inertial device. Applying magnetic torque to the superconducting rotor to compensate for the magnetic disturbance torque generated by centrifugal deformation is one of the effective methods to improve the measurement accuracy of the inertial device made of a superconducting rotor. To compensate for the magnetic disturbance torque caused by centrifugal deformation accurately, we studied the centrifugal deformation effect of the rotating superconducting rotor. In this paper, the centrifugal deformation of the superconducting rotor is analyzed first. And then the influence of centrifugal deformation of the superconducting rotor on magnetic force was studied by Finite Element Method (FEM). The results show that centrifugal deformation can reduce the magnetic levitation force of the superconducting rotor, leading to suspension position drift. Finally, the drift speed of the superconducting rotor's polar axis caused by centrifugal deformation is investigated, including the drift speed caused by centrifugal deformation of the rotating superconducting rotor, as well as the drift speed generated by the coupling of centrifugal deformation and suspension position drift of the superconducting rotor. The research results provide a reference for more accurate compensation of magnetic disturbance torque caused by centrifugal deformation and further improve the accuracy of superconducting rotor inertial devices.