The HTS Conductor on Round Core (CORC) Cables have been widely recognized as the proper candidate for superconducting applications such as the high-field magnets and power transmission cables. This article presents the modeling of HTS CORC cables using the FEM H formulation model merged into the package COMSOL Multi-physics. The 2D and 3D H formulation models of HTS CORC cables were compared and analyzed. There were two important parameters in our CORC design: (1) the gap angle between the HTS tapes in a single layer, and, (2) the degree of twist for each HTS tapes (normally identified as the pitch). The 2D CORC model has much faster solving speed over the 3D model and sometimes is able to model the AC loss in a reasonable range, while, the 3D CORC model has the advantages over 2D CORC model with respect to more information in each sector with the different conditions of two parameters above, and more realistic loss calculation.

Cables made by HTS tapes usually have anisotropic dependence by magnetic field owing to the inherit anisotropic characteristics in HTS materials. By increasing number of tapes, the perpendicular magnetic field components weaken the critical current of the whole conductor, and also lead to larger AC loss during AC operation. To reduce the AC loss from stacked HTS conductors, this article studies gap optimization schemes between non-twisted stacked HTS tapes. Finite element modeling with performance comparisons for a stacked HTS conductor (10 tapes) using non-uniform schemes is demonstrated. The results indicate that gap optimizations have better impacts in AC loss reduction rather than those direct stacked conductors. Designs using non-twisted configurations would be simpler, cheaper, and more robust. Therefore, the gap optimization method can be used to explore high current design for large-scale HTS applications.

Due to the anisotropy of high-temperature superconducting (HTS) materials, the stacked HTS conductors in a magnetic field are significantly affected, leading to a substantial reduction of critical current. In order to improve the performance of stacked conductors, we optimized the gap between these stacked tapes. First, we conducted experimental tests with four stacked tapes, and the results indicated that the critical current increased by about 5%. In order to explore the effect of the gap optimization scheme on the current distribution, we set up a model with 10 stacked conductors. Through modeling, it was found that the optimized gap scheme could improve the current distribution and increase the overall current carrying capability. This study provides a feasible optimization scheme for the design of high-current stacked HTS conductors, which can potentially enhance their performance in practical engineering.

The High-temperature Superconducting (HTS) magnet is one of the most promising technologies to accommodate various high field applications. With the high magnetic field, the quench problem of HTS material should be considered with extra care, and the specific quench protection scheme should be projected. In this article, the modeling of the quench protection of an HTS magnet for the MRI system is presented. The modeling strategy was composed of two stages: Stage 1 the HTS magnet was in the normal operation circuit, and Stage 2 the HTS magnet was switched to the heat dissipation circuit. The 1st stage was based on the finite element method (FEM) using the H formulation together with the thermal-coupled model, which simulated the current distribution of typical HTS tapes and showed the process of temperature increase when the hot source occurred. The 2nd stage was based on the analytical model to investigate the reasonable damping resistance and the hot spot temperature of the HTS magnet.

In this paper, we study the nonlinear optical bistability (OB) in a symmetrical multilayer structure. This multilayer structure is constructed by embedding a nonlinear three-dimensional Dirac semimetal (3D DSM) into a Fabry–Perot cavity composed of one-dimensional photonic crystals. The OB phenomenon stems from the third order nonlinear conductivity of 3D DSM. The local field of resonance mode could enhance the nonlinearity and reduce the thresholds of OB. This structure achieves the tunability of OB due to the fact that the transmittance could be modulated by the Fermi energy. It is found that the OB threshold and threshold width could be remarkably reduced by increasing the Fermi energy of the 3D DSM. Besides, we also found that the OB curve depends heavily on the angle of incidence of the incident light, the structural parameters of the Fabry–Perot cavity, and the position of the 3D DSM inside the cavity. After parameter optimization, we obtained OB with a threshold of ${10}^6 \mathrm{V}/\mathrm{m}$. We believe this simple multilayer structure could provide a reference idea for realizing low-threshold and tunable all-optical switching devices.

Bi-2223/Ag multifilament superconducting tape has high critical temperature, high critical current, and low loss, which has great application potential in superconducting power devices. However, it is a multifilament structure, and it takes a long time to use the finite element method (FEM) to simulate its electromagnetic and thermal properties. A method called “homogenization” is applied to quickly evaluate the electromagnetic characteristics of multifilament tape under normal alternating current. However, further research is needed to determine the applicability of the homogenization model under fault currents. In this paper, we use the electromagnetic-thermal coupling model to compare and analyze the loss and temperature change of the original model and the homogenization model tape under normal alternating current and fault current. Under normal alternating current, the temperature rise of the tape can be ignored, so the influence of temperature on the loss of the tape can be ignored. At this time, the homogenization model can quickly and effectively evaluate the AC loss of multifilament tape. Under the fault current, when the fault degree is small (Ip/Ic0 is less than 1), the tape temperature rise is not obvious, and the difference between the two models is small. At this time, the homogenization model can still quickly and effectively evaluate the loss of multifilament tape. When the fault degree is large (Ip/Ic0 is greater than 2), the temperature rise of the tape obtained by the two models is significantly different, so the tape loss obtained by the two models is somewhat different. At this time, the homogenization model should be carefully selected to describe the loss of multifilament tape.