Haigening Wei

High-temperature superconducting (HTS) CORC cables are promising candidates for next-generation high-field fusion and energy-storage magnets because of their compact geometry, mechanical flexibility, and high current-carrying ca pability. However, when such conductors are bent into coils, the curvature alters the local magnetic-field distribution and may influence the AC losses. This work presents a three-dimensional f inite-element model based on the T–A formulation to investigate the electromagnetic behavior of CORC cables under controlled bending. Systematic simulations for bending radii between 90 and 192 mm reveal a non-monotonic dependence of AC transport and magnetization losses on curvature. The initial increase arises from curvature-enhanced normal fields, the subsequent dip from interlayer magnetic cancellation, and the final rise from current concentration near the inner arc. Under ramp-current excitation, the peak loss per unit length exhibits a weak sensitivity to bending. These results suggest that CORC cables retain stable electromagnetic performance even in compact coil geometries.

Transformer–rectifier flux pumps offer an effective and contactless means to supply current to high-temperature superconducting (HTS) magnets, significantly reducing thermal losses associated with conventional current leads. They have demonstrated high-current capability and the ability to sustain target currents and magnetic fields over extended periods by compensating for inherent flux dissipation, showing promise for compact, cryogen-free superconducting systems. However, while liquid nitrogen are well studied, the stability of conduction-cooled systems remains insufficiently investigated. This paper presents an experimental study on the bridge quench behavior of a conduction-cooled half-wave transformer–rectifier HTS flux pump. By varying the amplitude and frequency of the applied AC magnetic field, the relationship between dynamic losses, bridge temperature rise, and quench initiation was analyzed. The results reveal that excessive field amplitude leads to localized resistive transition and voltage spikes, which suppress flux pumping efficiency and introduce current ripple. Comparisons with LN₂ cooling confirm that inadequate heat removal is the dominant factor limiting system stability.

High temperature superconducting (HTS) stacks of superconducting tapes provide a solution for all-superconducting electrical machines since they could work as trapped-field magnets. Most experiments with these stacks use pieces of tapes with relatively small areas as wider tapes are more difficult to acquire, therefore in this paper we investigate substitutions for these wider tapes to be implemented in superconducting electrical machines. With different stack architectures and substrate materials made by different manufacturers with different widths, the magnetizing effect using pulse field magnetization (PFM) would be different. To explore the differences of this effect, different stacks are tested in a modified synchronous machine designed by ASuMED under liquid nitrogen conditions. By changing the stacks of the tape and testing them under the same condition, the characteristics of the trapped flux, magnetization and demagnetization are affected, the difference is then compared to a COMSOL finite element model using an electromagnetic-thermal coupled model to investigate this effect. This paper shows the experimental setup for a PFM for HTS stacked coated conductor (CC) within an electrical machine, different stack architectures are tested and simulated, and the magnetic characteristics are compared and discussed, where the simulation and experiment agree in a certain degree, and the sectioned HTS CC stacks can proven to be useful in an electrical machine.

The high-temperature superconducting (HTS) Roebel tape is a latest developed concept of high-current and low-loss HTS cables for high-power AC applications. In this work, samples of Roebel tapes with single superconducting layer are manufactured, tested, modelled, and analysed. In the experiments, the critical current degradation and the transport AC losses are measured. In the simulation, with the 3D finite element method (FEM) models based on the T-A formulation, the transport AC losses are calculated and compared with the experimental data, and the current distribution is analysed in detail. This model is then used to simulate long HTS Roebel tapes which could be used in practice and calculate the transport AC losses. The losses are found over 30% lower than that of the normal HTS ReBCO tapes, which verifies the loss-reduction performance of the HTS Roebel tapes. This work provides both experimental and simulation proof of the advantage of the HTS Roebel tape as a high-current and low-loss HTS cable. It could potentially become the key to the compact fusion magnets which require high power density and suppressed losses.

Stacked high-temperature superconducting (HTS) coated conductors (CCs) are preferred for trapped field magnets over HTS bulk due to their improved mechanical strength and shape flexibility. In superconducting machines, the demagnetisation phenomenon in HTS CCs is crucial as it affects the machine's magnetic field loading, affecting power and torque output. The stator slotting effect, common in conventional machines, can also influence TFMs made from HTS CCs in superconducting machines, leading to magnetic flux distortion and additional losses. To gain a comprehensive understanding of these influences, numerical analyses based on the finite element method have been conducted for different variants of a superconducting machine. Findings indicate that in the machine model: (1) a slotted stator yields higher trapped field values compared to a slotless stator, and (2) closed slots prove effectively in eliminating air gap harmonics. A final design with distributed winding and closed slots is recommended for reference in HTS motor development.

The use of High-temperature superconducting (HTS) flux pumps has emerged as a promising approach for energizing HTS magnets. Compared to conventional power supplies, HTS flux pumps enable the wireless injection of a substantial dc current into a closed HTS magnet, allowing the magnets to operate in a persistent current mode. There are a lot of advantages to energize the HTS magnets in this manner. First of all, it avoids sophisticated power supplies and heavy current leads. Secondly, excessive cryogenic losses caused by thick warm-to-cold current leads can be reduced. Additional benefits include cost-effectiveness, reduced energy consumption, and a compact form factor. The most important parameter to evaluate the performance of the flux pump is its dc output voltage, which determines the charging capability. In this paper, we study both instantaneous and time-averaged dc output voltage for two most popular flux pumps – transformer-rectifier flux pump (TRFP) and high-Tc superconducting dynamo by a finite-element method model. Moreover, their working principles, structures and operation strategies are discussed. This work reveals characteristics and limitations of two flux pumps and is indicative for designing a high performance HTS flux pump for the specific application.

Magnetic Resonance Imaging (MRI) scanner consists of five major components: The main magnet, a gradient system, an RF coil system, a receiver, and a computer system for data acquisition. Gradient coils are an integral part of an MRI system, used for spatially encoding the MRI signal via modulations on the main magnetic field. In this article, we discuss the in-house design and production method of a particular gradient coil aimed as a part of a portable MRI instrument with a 1 T high-temperature superconducting (HTS) main magnet. We aim to reveal a clear path for those who want to follow.

High temperature superconducting (HTS) stacks of superconducting tapes provide a solution for all-superconducting electrical machines since they could work as trapped-field magnets. Most experiments with these stacks use pieces of tapes with relatively small areas as wider tapes are more difficult to acquire, therefore in this paper we investigate substitutions for these wider tapes to be implemented in superconducting electrical machines. With different stack architectures and substrate materials made by SuperOx, AMSC and THEVA, the magnetizing effect using pulse field magnetization (PFM) would be different. To explore the differences of this effect, sectioned stacks are tested in a modified synchronous machine designed by ASuMED under liquid nitrogen conditions. By changing different sectioned stacks of tape and testing them under the same condition, the characteristics of the trapped flux, magnetization and demagnetization could be affected, different stacks are simulated with COMSOL finite element models using an electromagnetic-thermal coupled model, and different stacks are tested with different charging voltages.

The Roebel tape is a novel high-temperature superconducting (HTS) wire with a multiple superconducting layer structure. Adjacent layers are patterned into meander-shaped multifilaments in opposite directions so that the magnetic fields generated by each layer can be mutually cancelled. The Roebel tape can be regarded as an HTS Roebel cable encapsulated into a tape, and hence has exclusive advantages such as high engineering current density, small critical current degradation, low AC losses, and a simple manufacturing process. This paper focuses on the transport AC losses of the Roebel tape with a multiple-layer structure. 3-D finite element method (FEM) models for the Roebel tapes are built based on the T-A formulation. Current distribution and AC losses of the Roebel tapes with up to 10 ReBCO layers are obtained. The results show that the tapes with even numbers of layers generate lower losses than those with odd numbers, which indicates the superconducting layers should always appear in pairs. Increasing layers can increase the engineering current density of the tape, but the average loss per layer also rises. Therefore, we suggest increasing the distance between the layer pairs or using double-layer Roebel tape stacks instead. The results indicate that the multilayer Roebel tapes can be a promising cable solution for industry and fusion applications because of the high current density and low AC losses.

When a type II superconductor carrying a direct current is subjected to a perpendicular AC magnetic field, a DC voltage can be observed, commonly referred to as “dynamic resistance effect”. This dc voltage appears in a very short time when AC field is applied and disappears quickly when AC field is removed. These advantages make the type II superconductors to be a fast AC-field-actuated HTS switch, which plays an important role in many potential high-temperature superconducting (HTS) applications, especially for HTS flux pumps or HTS magnetic energy storage systems. However, the temperature in the superconductor varies due to this dc voltage and may result in quench for the superconductor. Therefore, it is important to investigate the thermal behavior of an AC-field-actuated HTS switch. In this paper, we build and experimentally verified a 2D electromagnetic-thermal coupled model to investigate the electromagnetic-thermal characteristics of HTS switches in different working conditions. This model can estimate the dynamic voltage rise and the temperature rise of the superconductor. This work is indicative for designing an AC-field-actuated HTS switch in terms of increasing the dc voltage, and enhancing the safety and stability.