Physica C-superconductivity and Its Applications最新文献

A preliminary design of a Rutherford cable (Rfc) consisting of a copper core and 10 Quasi-isotropic Strands (Q-ISs) with symmetrical geometry is proposed. The current sharing temperature (T_cs), minimum quench energy (MQE), and normal zone propagation velocity (NZPV) are significant for determining the thermal stability performance of the superconducting cable. Firstly, an electric model of the conductor equivalent circuit is established, and the algebraic equations are derived. The model is validated with the empirical formula by calculating the T_cs of a single Q-IS. Using the validated model, the T_cs of Rfc fabricated by Q-ISs operating in liquid helium temperature at different magnetic fields are obtained. Then, to quantitatively characterize the effect of Q-ISs located at different positions on Rfc after a heating disturbance, the MQE and NZPV of Rfc are numerically simulated by the finite element method, which uses a 3-D thermal model with a homogenization procedure and coupled with the previous electrical model. The analyzed results provide a preliminary assessment of the thermal stability of the high-current superconducting cable and provide important guidance for subsequent experiments and prospective engineering applications.

The Bi₂Sr₂CaCu₂O_8+x (Bi-2212) material, a high-temperature superconductor, holds significant promise for future high-field applications because of its multifilamentary, twistable production capabilities, coupled with a high upper critical field. Bi-2212 round wire (RW) is made by the powder-in-tube (PIT) technique, and Bi-2212 coils are usually being developed using the wind-and-react method and a high temperature and over-pressure (OP) heat treatment (50 atm, 890℃) is then required to achieve the high current performance. However, over-pressure (OP) heat treatment can lead to a reduction in wire diameter, compromising the stability of the coil structure. Addressing this issue, the pre-overpressure (pre-OP) heat treatment is used and proves effective in mitigating the reduction in Bi-2212 wire diameter. In this paper, to comprehensively investigate the impact of pre-OP heat treatment on the microstructure of Bi-2212 wire, a metallographic analysis of two kinds of Bi-2212 wires was carried out by the scanning electron microscope (SEM) and the ImageJ software. It was found that larger-area filaments experienced a greater reduction in area after pre-OP heat treatment, that pre-OP heat treatment increases the aspect ratio of filaments, and polygonal bundle structure helps maintain filament structure stability during pre-OP heat treatment. Additionally, the impact of pre-OP heat treatment on the performance of Bi-2212 wires was analyzed through critical current testing under high fields.

We found a significant difference between the central and end magnetic field delays during the testing of a metal-insulation (MI) high-temperature superconducting (HTS) magnet. In this paper, we first analyzed the reasons for the difference in the field, and the results show that it is mainly due to the difference in the characteristic resistance of each double pancake (DP) coil. We further evaluated the effect of the difference on the electromagnetic analysis results of the MI HTS magnet. Subsequently, we developed an equivalent circuit model that considers the difference in the characteristic resistance of the DP coils and used the model to analyze the effect of this difference on the fields and losses generated by the MI HTS magnets, especially for AC conditions. Finally, based on our analytical results, a coil arrangement strategy considering the characteristic resistance of each DP coil was proposed. This work can guide us in evaluating the magnetic field more accurately in future engineering applications and provide a coil arrangement strategy for the MI HTS magnet, which requires to excite rapidly or generate an alternating magnetic field.

CORC superconducting cable is a compact and flexible composite superconductor. It is widely used in large power systems because of its good flexibility and high engineering current density. In these applications, reducing the AC loss generated by the superconductor is a key factor in studying the electromagnetic field of the superconducting conductor, which affects the operational stability of the entire superconducting power device. Currently, the use of striated tape-wound cables not only allows for flexible wiring at design time but also effectively reduces AC losses. This technology has been widely used in large superconducting magnet equipment. In this paper, the finite element model of single superconducting tape and CORC superconducting cable is established based on the finite element idea. The electromagnetic properties and mechanical changes are numerically calculated by H-method. The results show that both the current density and the magnetic field of a single superconducting tape show a gradual penetration from the two sides to the center. The area of maximum current density and magnetic field distribution is at the tape boundary. The distribution of current density, magnetic field and Lorentz force of three-dimensional CORC superconducting cable is similar. All of them are gradually attenuated from the maximum value at the boundary to the center position. It is worth noting that the current density, magnetic field and Lorentz force of the striated superconducting cables are smaller than the values without striations. The calculation results of the finite element model in this paper show that the striations weaken the current density, magnetic field and Lorentz force of the CORC superconducting cable by about 8.77%, 16.21% and 9.23%. Moreover, the presence of striations can effectively reduce the AC loss of superconductors.

This paper presents a novel joint-less toroidal magnet made of second-generation high-temperature superconducting (2G-HTS) tapes. This approach effectively resolves the closed-loop issue for 2G-HTS magnets and has the potential to provide higher and more stable magnetic fields. Compared with traditional 2G-HTS toroidal magnets, while the current loops of the joint-less magnets have no resistance, a decrease in magnetic field still occurs, especially in coils with insulation. Therefore, this work focuses on the decrease of the magnetic field of this novel magnet using experimental and microanalytical methods. For the first time, it was verified that, by winding two coil groups, insulated and no-insulated, parallel charging does not cause interference between them. Furthermore, the magnetic field area was expanded by finite element analysis, and simulations showed that the magnetic field converged with increasing number of coils. Besides, we found that the decrease of the magnetic field was related to the damage of the tape during slitting and winding, where insulated coils were more susceptible to damage during winding. The damage usually occurred at the starting point of the tape slitting, because the copper layer was separated due to adhesion during the winding of insulated coils, which further caused the superconducting layer to detach, resulting in a decrease in the critical current. From our perspective, benefiting from the high critical field of the 2G-HTS tapes, this novel toroidal coil structure has significant implications for the construction of compact toroidal magnets.

Motivated by recent scanning tunneling microscopy experiments on Fe atomic line defect in iron-based high temperature superconductors, we explore the origin of the zero energy bound states near the endpoints of the line defect by employing the two-orbit four-band tight binding model. With increasing the strength of the Rashba spin–orbit coupling along the line defect, the zero energy resonance peaks move simultaneously forward to negative energy for $s_{+-}$ pairing symmetry, but split for $s_{++}$ pairing symmetry. The superconducting order parameter correction due to As(Te, Se) atoms missing does not shift the zero energy resonance peaks. Such the zero energy bound states are induced by the weak magnetic order rather than the strong Rashba spin–orbit coupling on Fe atomic line defect.

Thermal switching by applying magnetic field is one of the key technologies in thermal management in electronic devices. In low-temperature devices, superconductors can be used as a magneto-thermal-switching (MTS) materials due to the large change in carrier thermal conductivity by the superconducting transition. In this study, we measured the temperature (T) and magnetic field (H) dependences of thermal conductivity (κ) of Sn, Ta and V to enrich knowledge on MTS of type-Ⅰ and type-Ⅱ superconductors. From the data analyses, we found different trends of κ-H curves in type-Ⅰ and type-Ⅱ superconductors. The normalized κ-H curves of type-Ⅰ superconductors showed the similar behavior, which is solely governed by H_c. However, the κ-H curves of type-Ⅱ superconductors were affected by the H_c1 and H_c2, and its behavior greatly depends on the materials. In addition, we investigated the elemental composition of Sn and Ta to explore the origin of weak hysteresis in the κ-H curves and revealed the importance of impurity on the hysteresis of κ-H curves.

Reservoir computing, which takes advantage of physical phenomena with nonlinearities, is attracting a lot of attention. Therefore, it is expected to focus on superconductivity, a physical phenomenon with nonlinearities between the output electric field and the input current density. Compared to other physical phenomena used in reservoirs, it is considered that with superconductivity, the nonlinearity can easily be adjusted spatially by pin placement to produce dynamics suitable for reservoirs. The nonlinearity between the electric field generated by the motion of the quantized magnetic flux lines and the input current density was used to perform a reservoir computing task. Three waveform generation tasks, a NARMA2 task and a nonlinear-memory task were performed, and all tasks were generally successful. It was found that the electromagnetic phenomenon in superconductors can be used as a physical reservoir.

A recent Little-Parks experiment on the new Kagome superconductor CsV${}_3$Sb${}_5$ demonstrated resistance oscillation with a period of ${\varphi }_0/3=hc/6e$. This observation of charge-$6e$ flux quantization is effectively explained by a three-component Ginzburg–Landau (GL) model that incorporates second-order Josephson-type couplings. Here, we numerically solve the GL model to present stable topological solitons. We reveal the structures of these solitons, characterized by closed domain walls with attached vortices. We identify two types of domain walls. These solitons possess multiple flux quanta and exhibit a ringlike geometry. Furthermore, we present the characteristic magnetic field distributions of these solitons, enabling their identification in, e.g., scanning Hall probe and scanning SQUID experiments.

In this work we study the role of the heat diffusion equation in simulating the resistive state of superconducting films. By analyzing the current–voltage and current-resistance characteristic curves for temperatures close to $T_c$ and various heat removal scenarios, we demonstrate that heat diffusion notably influences the behavior of the resistive state, specially near the transition to the normal state, where heat significantly changes the critical current and the calculated resistance. Furthermore, we show how the efficiency of the substrate has important effects in the dynamics of the system, particularly for lower temperatures. Finally, we investigate the hysteresis loops, the role of the film thickness and of the Ginzburg–Landau parameter, the findings reassuring the significance of accounting for heat diffusion in accurately modeling the resistive state of superconducting films and provide valuable insights into its complex dynamics. To accomplish these findings, we have used the $3D$ generalized Ginzburg–Landau equation coupled with the heat diffusion equation.