Superconducting Coil Research Articles

Performance analysis of superconducting motors for electrical aircraft propulsion using electromagnetic–thermal coupling method

The aviation industry is focusing on the development of low-carbon emission technologies, with hydrogen-powered aviation hybrid technology being an important area of interest. Superconducting motors (SCMs) play a crucial role in these aviation hybrid systems due to their high power-to-weight (PTW) ratio. However, SCMs face challenges such as strong coupling of the electric field, magnetic field, and temperature field within the motor. Conventional electromagnetic–thermal coupling analysis methods are not suitable for SCMs, as they are slow to perform calculations that are also less accurate. This study proposes an electromagnetic-thermal coupling analysis model for SCMs, taking into account the constraints of critical current, critical magnetic field, and critical temperature of superconducting (SC) materials. The study analyzes the impact of the critical current of SC tapes, permanent magnet remanence, convection heat transfer coefficient between SC coils and cooling medium, AC loss reduction of SC coils, and motor speed on the ultimate power of SCMs. The results show that an optimal permanent magnet remanence can maximize the ultimate power, and the other parameters have been found to be positively correlated with the ultimate power of the SCM. To enhance the PTW ratio of SCMs, future research directions include increasing the critical current of SC materials, reducing the AC loss of SC coils, and improving the cooling effectiveness of SC coils.

Development of a novel multifunctional superconducting device for performance enhancement of DC microgrids

DC microgrids have become an important infrastructure for increasing the integration of renewable energy sources in power grids. However, these DC microgrids suffer from inherent fluctuations from renewable energy sources as well as high fault currents during grid disturbances. Addressing these challenges simultaneously with a single device is a significant technical issue. This paper proposes a novel Multifunctional Superconducting Device (MSCD) with dual functionality to overcome these challenges. The MSCD can operate as a Superconducting Magnetic Energy Storage (SMES) system during normal operation, providing mitigation of renewable energy fluctuations through its shunt connection. During grid faults, the MSCD transits to operate as a Superconducting Fault Current Limiter (SFCL) in series with the grid, limiting the fault current. The proposed MSCD has only an additional controlled switch to the conventional power electronic converter of SMES. The dual functionality of the proposed MSCD has been evaluated using the PSCAD/EMTCD computer package under various operating conditions, validating its ability to seamlessly transition between SMES and SFCL modes. The proposed MSCD could effectively smooth DC bus voltage fluctuations caused by variations in wind speed and solar radiation and could significantly limit the fault current contribution from the DC microgrid under fault conditions. Furthermore, a superconducting coil with a pancake structure has been built and integrated with a control circuit to experimentally validate the functionality of the MSCD. Two experimental case studies were conducted - the first testing the charging and discharging behavior, and the second evaluating the current limiting capability of the MSCD prototype.

Novel multi-modular power conditioning system and decoupling control strategy for SMES with coupled superconducting coil

The high-temperature superconducting magnetic energy storage system (HTS-SMES) utilizes a superconducting coil (SC) to store electric energy in a magnetic field. It has several advantages such as high efficiency, fast response, and infinite charge–discharge cycles. Coupling two SCs made of different HTS materials, known as coupled SC (CSC), can enhance the utilization rate of HTS tapes, reduce manufacturing costs, increase the energy storage density of the SC, and lower magnetic leakage. However, the presence of a coupled magnetic field in CSC makes precise power and current regulation of the individual SC challenging. Additionally, the self-inductances of the individual SCs, composed of different materials, typically differ from each other. Consequently, the current variation induces electromotive force in each SC that differs from the others, necessitating the design of power converters with different voltage ratings connected to each SC. To address the difficulties associated with SMES implementation using CSC, this paper proposes novel modular power conditioning system (MPCS) and decoupling control strategy for SMES. The MPCS enables the flexible design of individual SC power ratings by selecting the appropriate number of power modules. The decoupling control ensures precise current control of each individual SC, which significantly reduces the current ripple of the SCs. Moreover, by employing carrier phase shift modulation, the total harmonic distortion (THD) of the PCS output current is as low as 0.79%. Furthermore, the feedforward power control is proposed to reduce the power control overshoot, and the current sharing control is presented to ensure precise current sharing between each SC. Simulation results verify the efficacy of the proposed approaches.

Holistic numerical simulation of a quenching process on a real-size multifilamentary superconducting coil

Superconductors play a crucial role in the advancement of high-field electromagnets. Unfortunately, their performance can be compromised by thermomagnetic instabilities, wherein the interplay of rapid magnetic and slow heat diffusion can result in catastrophic flux jumps, eventually leading to irreversible damage. This issue has long plagued high-Jc Nb3Sn wires at the core of high-field magnets. In this study, we introduce a large-scale GPU-optimized algorithm aimed at tackling the complex intertwined effects of electromagnetism, heating, and strain acting concomitantly during the quenching process of superconducting coils. We validate our model by conducting comparisons with magnetization measurements obtained from short multifilamentary Nb3Sn wires and further experimental tests conducted on solenoid coils while subject to ramping transport currents. Furthermore, leveraging our developed numerical algorithm, we unveil the dynamic propagation mechanisms underlying thermomagnetic instabilities (including flux jumps and quenches) within the coils. Remarkably, our findings reveal that the velocity field of flux jumps and quenches within the coil is correlated with the cumulated Joule heating over a time interval rather than solely being dependent on instantaneous Joule heating power or maximum temperature. These insights have the potential to optimize the design of next-generation superconducting magnets, thereby directly influencing a wide array of technologically relevant and multidisciplinary applications.

FPGA-Stabilized Magnetic Levitation of the APEX-LD High-Temperature Superconducting Coil

FPGA-Stabilized Magnetic Levitation of the APEX-LD High-Temperature Superconducting Coil

Quench behaviors of parallel-wound no-insulation high temperature superconductor coils

Quench behaviors of parallel-wound no-insulation high temperature superconductor coils

Analysis and Verification of cooling structure of superconducting motors for electrical aircraft propulsion

The hydrogen-powered aviation hybrid technology is one of the important directions of the development of electrical aircraft propulsion. Superconducting motors (SCMs) are the core components of a hydrogen-powered aircraft due to their high power-to-weight ratio. Among SCMs, partial SCMs with superconducting armature windings and permanent magnets (SC-PMMs) are the research front and hotspots. This study focuses on the key issue of cooling the superconducting (SC) coils of SC-PMMs. The advantages and disadvantages of three cooling structures, namely core conduction cooling, coil immersion cooling, and core and coil immersion cooling, are compared. The temperature of the SC coils in different cooling structures is simulated and analyzed in detail. The obtained results show that the temperature of the coils in the core and coil immersion cooling structure is not much different from that in the coil immersion cooling structure, with a temperature difference of about 1.5 K only. However, the implementation of the core and coil immersion cooling structure is much easier. Therefore, an SC-PMM prototype is developed using it as the cooling structure, and the temperature change in the prototype under different operating conditions is investigated experimentally. The obtained results show that the final stable temperature during the cooling process is 76.8 K, and the coil on the top is more likely to quench than that at the bottom. The maximum frequency and maximum current at which the prototype can operate stably for a long time are 200 Hz and 49 A, respectively. This study verifies the effectiveness of the core and coil immersion cooling structure, obtains the quench prone area in SC-PMMs, and lays the foundation for the development of high-performance and highly reliable SCMs.

Сверхпроводниковая электромагнитная система ИТЭР. Статус изготовления и сборки на 2024 год

The electromagnetic system (EMS) is one of the most significant components of the International Thermonuclear Experimental Reactor (ITER). It establishes the machine’s ability to generate and control a fusion plasma with a current of up to 15 MA and a power of up to 500 MW within hundreds of seconds. ITER EMS is the largest superconductor magnet system that has ever been created with a stored energy of up to 50 GJ. It is a highly technological magnets using superconductors based on Nb3Sn and NbTi, which work at a temperature of 4-6 K with compulsory cooling by a flow of liquid and gaseous helium. The EMS coils are required to be operable at electrical voltages up to 20-30 kV, and mechanical stresses up to 500-600 MPa. The manufacturing of the coils and the associated superconducting current carrying system are now moving into the final stage of production. The most part of them has already been manufactured and delivered to the ITER toroidal magnetic coil chamber (Tokamak) installation site. This review briefly describes the design of ITER superconductor coils of all 4 types and gives the current status of their manufacturing and assembly.

Double-pancake superconducting coil integrated with DFIG-based wind power systems under voltage-dip events: Design and performance analysis study

The doubly fed induction generator (DFIG)-based wind turbine provides massive development in power generation. Uncertain power oscillations and voltage-dip events affect the stability of the DFIG. To mitigate the effect of voltage-dips in short period, superconducting magnetic energy storage (SMES), which possess rapid energy exchange and high power density, is integrated with large-scale renewable power systems. SMES is integrated at the DC link of the DFIG to ensure the power balance and fault ride-through (FRT) capability. During this operation, frequent current changes occur in the high-temperature superconducting (HTS) coil, which leads to an increase in AC losses. As a remedy, an additional power converter structure controlled with a model-predictive controller (MPC) is proposed. Firstly, a scale-down HTS double-pancake coil model is designed using a finite element model by which transport current loss and magnetic field formulation are studied. Additionally, the critical coil current is also verified through experimental studies. The effectiveness of the proposed MPC-based SMES integrated DFIG on DC link voltage and grid current under IEC-61000-4-11 standard, symmetrical and asymmetrical voltage-dip cases are investigated. The obtained results demonstrate that the proposed system effectively reduces transients in DC link voltage and improves the FRT capabilities of the grid.

Investigation of the energizing characteristics of a metal-insulation iron-based superconducting coil

With the progress of iron-based superconducting wire and tape fabrication technologies, extensive research has been conducted on iron-based superconducting coils. A deep understanding of the energizing characteristics of these coils is crucial for their large-scale application. This study investigates two metal-insulated double pancake coils, each having a different number of turns and co-wound with Ba0.6K0.4Fe2As2 iron-based superconducting tape and stainless-steel tape. We conducted critical current tests, sudden-discharge experiments, and charge-discharge cycles at 4.2 K to obtain the time constants and characteristic resistances of the coils. Additionally, the impact of stainless-steel as co-wound material on coil performance was analyzed. Theoretical models were employed to calculate the charging processes and validate them against experimental results. This research offers valuable insights for the practical application of iron-based superconducting materials.

Enhanced visualization of quench dynamics of HTS coils through embedded and distributed fiber optical sensing

The development of high-temperature superconducting (HTS) coils and magnets marks a significant advancement across various fields. To ensure their safety and reliability, thorough performance testing under extreme multi-field conditions is essential. This study introduces an innovative method that utilizes embedded and distributed fiber optical sensing (ED-FOS) in HTS pancake coils for precise real-time thermal monitoring and quench visualization. Incorporated during the manufacturing process, the ED-FOS sensors offer comprehensive and distributed measurements of thermal behavior during quenches. Our experiments demonstrate the ED-FOS effectively detects quenches caused by overcurrent and thermal issues. Unlike conventional techniques that rely on global voltage or magnetic field assessments, ED-FOS provides high spatiotemporal resolution and enhances temperature sensitivity. This capability allows for accurate, real-time identification and tracking of quench locations, which is essential for evaluating reliability and safety, as well as for improving performance. This advancement in HTS coil technology paves the way for wider application in critical fields and significantly enhances the design and management of superconducting coils.

Fast current discharging using self-coupling energy absorption for insulated high temperature superconductor magnets

Abstract Quench protection has always been challenging for high-temperature superconductor (HTS) coils. Fast current discharge after quench detection is important for a successful coil protection. The copper plates initially intended for cooling can significantly accelerate the discharging process for HTS coils through electromagnetic coupling between coils and copper plates. However, the underlying physical mechanism of this technique has not been studied thoroughly. Here we present a detailed study on the electromagnetic and thermal characteristics of HTS coils coupled with copper plates through experiments and simulations. The results show that a considerable current rebound occurs after an accelerating current drop in the early stage of the fast-discharging process. This coil current rebound is induced by temperature rise as well as the resistivity of copper plates, which are heated by induced eddy current. The heat transfer from copper plates can uniformly heat the whole coil rapidly, which speeds up the discharging process, meanwhile it can also induce overcurrent quench risk. A 30 T@20 K HTS magnet with 36 single pancakes (SP) is analyzed. The coupling copper plates can make the coil current drop to 36.9% within the initial 8 ms. The temperature rise induced by copper plates shows a considerable nonuniform distribution among the multiple coil systems. The protection can be enhanced by optimizing the resistivity of copper plates and magnetic coupling strength between plates and coils. This technique has great potential for the protection of insulated HTS magnets.

A fully superconducting magnetic bearing with a jointless coil excited by a superconducting dynamo

Abstract Superconducting magnetic bearings usually combine a setup of permanent magnets (PMs) and superconducting bulks. The bearing size is typically scaled up to increase the levitation force as the force density is limited in such setups due to the magnetic flux density and its spatial gradient. As alternative, the PMs might be replaced by a superconducting coil. To test this, jointless coils were prepared by a wind and flip technology using coated conductors of different tape manufacturers. The realized pancake coils were studied at liquid nitrogen temperature. Numerical simulations yielded a magnetic field of up to 0.5 T at 77 K for coils with a inner diameter of 20 mm. The prepared coils were charged with a superconducting dynamo, in which two magnet configurations were tested. A clear dependence on the magnet size and frequency was found for the charging characteristics. A magnetic field of about 0.3 T at 77 K was imprinted in one of the coils. However, a degradation of the coils was found over time indicated by some delamination at the cutted edges, which reduced the maximum achievable magnetic field after a few weeks. Nevertheless, a fully superconducting bearing was realized with by combining the jointless coil with an additional YBCO bulk. After charging the coil with the dynamo, a levitation force of up to 10 N at 77 K was measured under zero-field cooling conditions. The generated levitation force decayed only slightly after charging indicating low losses in the coil.

Overcurrent Quench Detection of Parallel-Wound No-Insulation High Temperature Superconductor Coil Based on Digital Twin Method

Overcurrent Quench Detection of Parallel-Wound No-Insulation High Temperature Superconductor Coil Based on Digital Twin Method

Current sharing in double-sided REBCO tapes

Current sharing between RE–Ba–Cu–O (REBCO, RE = rare earth) tapes within a high-temperature superconducting coil or cable is important to avoid damage from uncontrolled quench of superconducting devices operating at high currents. Current sharing between REBCO tapes is found to be limited by the contact resistivity between adjacent tapes, which is about 20x higher in the REBCO-facing-substrate (face-to-back) configuration that is commonly used in devices compared to a REBCO-facing-REBCO (face-to-face) configuration. Double-sided REBCO tapes always offer face-to-face contacts between adjacent tapes, and this benefit of excellent current sharing has been validated in experiments wherein an artificial defect is introduced in one tape in a 2-ply tape stack. Additionally, current sharing between the two REBCO layers within one double-sided REBCO tape has also been investigated. Slotting of the double-sided tapes, wherein slots through the insulating buffer stack are filled with a conductive material, has been found to significantly enhance the current sharing from one REBCO layer to the opposite layer.

Developments, Applications, and Perspectives of High-Field Generation Technology by High-Temperature Superconducting Coils

Developments, Applications, and Perspectives of High-Field Generation Technology by High-Temperature Superconducting Coils

Control of elongated plasmas in superconductive tokamaks in the absence of in-vessel coils

The roadmap for the commissioning and first operations of superconductive tokamaks envisages the possibility of running discharges with fairly elongated plasmas before the complete installation of the in-vessel components, including vertical stabilization coils, or any other specific sets of coils to be used for the magnetic control of fast transients. In the absence of dedicated actuators, the magnetic control system shall perform the essential fast control actions by using the out-vessel superconductive coils, if needed. These are typically less efficient in reacting to fast transients, due to the shielding effect of the vessel and imply a coupling with other control tasks relying on the same actuators, such as plasma current, position, and shape control. Hence, effective actuator-sharing strategies must be put in place. This paper presents an architecture and a possible control strategy that is able to cope with vertically unstable elongated plasmas subject to fast varying disturbances, in the absence of dedicated in-vessel coils. The architecture exploits a model-based actuator-sharing approach to effectively accomplish the main magnetic control objectives while minimizing the cross-couplings among the various tasks. The effectiveness of the approach is demonstrated by means of nonlinear simulations of realistic JT-60SA scenarios. In particular, an isoflux plasma shape controller is integrated with plasma current control and vertical stabilization. The proposed control approach proves to control vertical displacement events and plasma deformations due to fast variations of poloidal beta with satisfactory performance.

Qualification and test of space compatible superconducting current leads (REBCO) designed for adiabatic demagnetization refrigerators

Many astrophysics observations require space telescopes, either to reduce atmospheric perturbation or simply to make these detections possible (in the X-Ray spectrum for example). One of these missions, Athena, is led by the European Space Agency (ESA), with additional international contributions, dedicated to X-Ray observation. Two instruments will be part of this mission and among them, X-IFU, will use Transition Edge Sensors (TES) to detect and precisely measure the energy of X-Ray photons. These sensors require a temperature of 50 mK to reach their ambitious sensitivity goals. In space, this temperature can be reached using Adiabatic Demagnetization Refrigeration (ADR) and such a cooling system is currently being developed for the X-IFU instrument. ADR utilizes magnetocaloric materials which, upon variation in magnetic fields, can produce a cooling effect. The magnetic field of the order of 1 T in a volume of 10s of cm3 is produced by a superconducting coil with high winding number and current limited to approximately 2 A. Even though this current is low compared to most earth-based systems, metallic current leads to link the high- and low-temperature stages would cause high thermal loads, unacceptable for the limited capacity of the cryogenic cooling chain of the spacecraft. Therefore, a harness consisting of superconducting current leads is planned to reduce the thermal loads at the low-temperature stage. As part of an ESA contract, our team designed, built and tested such a space-compatible harness. This harness includes the electrical interfaces at both ends as well as mechanical support. Its development is capable of operating between interfaces at 80 K and 4 K. The harness is based on industrially available Rare-Earth-Barium-Copper-Oxide (REBCO) High-Temperature Superconductor (HTS) tapes. The tapes were laser-cut by our group to fulfill our specifications, Parylene coated and reinforced with Kapton laminate tape for mechanical and insulating purposes. After characterization of the single tapes, the assembled harness has been subjected to an extensive qualification sequence including thermal cycling and mechanical testing based on launch loads requirements. This paper will summarize the technical design choices for this HTS harness. It will discuss the test results and propose some perspectives for the next iteration of the development.

The Interaction Between a High-Temperature Superconducting Coil and In-Series Permanent Magnets

The Interaction Between a High-Temperature Superconducting Coil and In-Series Permanent Magnets

Effect of local and global screening current on the current decay in closed-loop HTS coils

High-temperature superconducting (HTS) coils are generally operated in a closed-loop persistent current mode, which is crucial for ensuring long-term stability and minimizing heat generation in various applications. However, factors such as joint resistance, flux creep, and losses due to external fields can lead to accelerated decay of the coil’s current, making it challenging to achieve an effective persistent current mode. To gain insight into the current decay characteristics of HTS coils, we built a finite element method based model coupled with a lumped parameter electric circuit model. The model is initially verified against the experiment of an inductive magnetized HTS coil subject to a magnetic field perpendicular to the tape surface. The results indicate that the proposed model is highly effective in predicting the current decay behavior of this magnetized HTS coil and is able to provide high accuracy. With the help of this model, we have experimentally and numerically studied the behavior of a current-carrying closed-loop HTS coil subject to external alternating fields. The HTS coil is charged by a DC power supply and then shorted using a thermally-controlled persistent current switch. The current decay behavior of the HTS coil is examined under various scenarios. The simulation results show excellent agreement with experimental data, further validating the effectiveness and versatility of the modeling strategy. The influence of both local and global screening currents on the current decay performance of the closed-loop HTS coils has been investigated. For every case examined, rapid demagnetization occurred in the initial cycle of the applied alternating field. Furthermore, the current decay rate demonstrated a slight dependence on the frequency of the applied fields. Additionally, the resulting resistance has been thoroughly characterized. These insights contribute to the knowledge of the behavior and performance of closed-loop HTS coils, facilitating their practical application.