High-temperature Superconducting Magnet Research Articles

Influence of D-Q Current on No-Insulated High-Temperature Superconducting Magnets for Wound-Rotor Synchronous Motors

Influence of D-Q Current on No-Insulated High-Temperature Superconducting Magnets for Wound-Rotor Synchronous Motors

The spherical tokamak path to fusion power: Opportunities and challenges for development via public–private partnerships

In this article, we aim to show that the spherical tokamak (ST) device with high temperature superconducting (HTS) magnets could offer the quickest and lowest risk path to develop commercial fusion energy, which may be significantly advanced by the use of private–public partnerships. Our starting point is based on what we have learned and will continue to learn from publicly funded research on STs. Keeping prototype ST devices and HTS magnets small has enabled rapid innovation toward a commercial goal. Our ST40 compact, high field ST has proven exceptional performance, with plasma ion temperatures over 100 × 106 °C (above 8 keV) and a record triple product for any private company (n T τE ∼ 1019 keV s/m3). Meanwhile, our robust, compact, quench-safe, HTS magnets can routinely achieve over 24 T. We now have results of great interest to fusion scientists, so as well as pursuing our commercial goals, we are contributing to scientific progress in fusion. Opportunities to participate in public–private partnerships are emerging with Tokamak Energy already selected for the U.S. Department of Energy milestone program and well-positioned to participate in the U.K. Government Spherical Tokamak for Energy Production program. Other countries are likely to adopt similar approaches as the need for rapid development of fusion energy becomes ever more apparent.

A numerical study on homogeneity and central field with axial spacing between DP coils of HTS magnet at 65 K

A numerical study is performed with COMSOL multi-physics, to analyze the effect of axial spacing between double pancake (DP) coils on central magnetic field and field homogeneity of High temperature Superconducting (HTS) magnet. The magnet is wound in the form of DP coils having, inner winding diameter as 100 mm and is operated at 65 K. The field homogeneity is calculated over a Diameter of Spherical Volume (DSV) of 40 mm for the entire study. The analysis is carried out by considering a constant length of HTS tape of 750 m and varying the number of DP coils from 4 to 14. The number of turns in all the DP coil is equal for a given set of DP coils to maintain the length of HTS tape to be constant. The coil separation within DP coils is of constant gap from 0.5 to 2 mm, while the axial spacing between the DP coils is varied from 0 to 50 mm for all the set of DP coils. The optimum gap between DP coils was evaluated using Exhaustive search optimization techniques and decreased with the number of DP coils. The best field homogeneity of 662.5 ppm was achieved with 14 DP coils having gDP=20.3 mm and gSP=2 mm for the chosen solenoid configuration.

Energy and exergy analysis of the cryogenic system for HTS magnets based on an open-cycle G-M/J-T cryocooler

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.

Feasibility study on quench detection methods of Raman and Rayleigh scattering techniques in optical fiber encapsulated HTS coils

Quench detection is a key issue to be solved for safe operation of high temperature superconducting (HTS) magnets. Recently, distributed optical fiber sensors based on Raman and Rayleigh scattering techniques are proposed for quench detection in HTS applications. However, sensing and demodulating principles of these two techniques are different, and they may show different performances in quench detection. In this paper, a 13 m long optical fiber encapsulated HTS coil (OF-coil) was fabricated. Two sensing devices based on Raman and Rayleigh techniques, which are named Raman-device and Rayleigh-device, were prepared. Overcurrent and heater induced quench detection experiments in the OF-coil were carried out and the above two devices were used for quench detection. The results show that both Raman-device and Rayleigh-device can measure temperature changes of the OF-coil in the overcurrent experiment. And their quench response time is 36 s and 14 s, respectively. In heater induced quench detection experiment, Rayleigh-device can successfully acquire local temperature rise of the OF-coil, and the quench response time is 1.7 s. For Raman-device, its spatial resolution is too large to realize local quench detection.

Gamma radiation effects on high-temperature superconducting ReBCO tape

High-temperature superconducting (HTS) magnets are crucial components in future fusion reactors, subjected to prolonged irradiation and complex mechanical conditions. While the irradiation sensitivity of HTS materials has been extensively studied, limited research has explored the effects of force conditions during irradiation. This study investigated the influence of irradiation on ReBCO tapes. An irradiation experiment was conducted utilizing a Co60 source irradiation device. Superconductor properties were evaluated through the induction method, while microstructure analysis was performed using x-ray diffraction measurements. The results indicate that the critical current initially increases and subsequently decreases, while the critical temperature remains relatively stable. Furthermore, the bending degree during irradiation affects the critical current density, with a decrease in radius corresponding to a first increase and then subsequent decrease in critical current density. The force applied during irradiation exhibits a impact on the superconducting properties, underscoring the importance of considering force conditions in future investigations.

Analysis of guidance and levitation forces between HTS magnets and conductive tubes for Hyperloop

High-temperature superconducting (HTS) magnets combined with linear synchronous motors and electrodynamic suspension (EDS) are considered as one of the most suitable technologies for Hyperloop. However, HTS magnets on pods generate strong magnetic fields, inducing eddy currents on conductive tubes when pods undergo movement through conductive tubes. The induced eddy currents affect HTS magnets, leading to electromagnetic (EM) drag, guidance, and levitation forces on the pods, thus reducing the propulsion efficiency and dynamic stability of pods. This study continues the existing research on EM drag forces between HTS magnet and tube for Hyperloop by comprehensively analyzing the EM guidance and levitation forces between HTS magnets and conductive tubes. Importantly, the full-scale 3D finite element analysis (FEA) simulations show that different steel tubes, such as AISI 1010 and high-manganese (Hi-Mn) steels, should be adopted, depending on the operating velocities, v, to avoid attractive forces in the guidance direction decreasing horizontal stiffnesses, For example, Hi-Mn tubes generating repulsive guidance forces are adopted when v is below 300 km/h while AISI 1010 tubes are used when v is over 300 km/h to minimize the construction cost of vacuum tubes to guarantee the increase in kx. For the proposed concept, the effect of the different tube connections on guidance and levitation forces is confirmed by the full-scale 3D FEA simulation. Moreover, levitation forces generated between HTS magnets and conductive tubes are nearly 0.5% of the EDS forces of pods, i.e., 200 kN over v of 150 km/h in the levitation direction. Therefore, the effect on vertical stiffnesses, ky, might be limited. In the end, to validate the proposed tube connections, the effect of the two different tube connections on guidance and levitation forces is confirmed by the full-scale 3D FEA simulation, and it was found that the sudden change in the guidance and levitation forces could be low enough to be neglected in the acceleration (from Hi-Mn to AISI 1010 steel tubes) and deceleration (from AISI 1010 to Hi-Mn steel tubes) regions.

Experimental study on the an-isotropic critical current of REBCO tape.

Superconducting magnets are widely used in nuclear fusion reactors, high-energy particle accelerators, steady-state high magnetic fields, etc. Higher magnetic fields and higher operating temperatures are two application trends. High temperature superconducting (HTS) materials are the only choice for high temperature and high field magnets in the future. The first- and second-generation HTS materials have a typical tape structure; their critical performance is magnetic field angle and temperature dependent. A new test facility is developed for an experimental study on the an-isotropic critical current. The field angle can be changed from 0° to 360° with a resolution of 1°. The rotation deviation angle is measured to be 0.2° when the upper part rotates 90°. The temperature can be changed from 4.2 to 80K. The temperature errors are ±50, ±80, and ±135 mK for 4.2-20, 20-40, and 40-80K, respectively. The angle dependence of critical current (Ic) of the tested rare-earth barium copper oxide tape within 0°-30° is strong. From 30° to 90°, the sample Ic almost does not change with the magnetic field angle. The implementation of the project will not only promote the structural optimization of HTS tapes but also promote the miniaturization and economical application of HTS magnets.

Cryogen-free 400-MHz nuclear magnetic resonance spectrometer as a versatile tool for pharmaceutical process analytical technology.

The discovery of new ceramic materials containing Ba-La-Cu oxides in 1986 that exhibited superconducting properties at high temperatures in the range of 35 K or higher, recognized with the Nobel Prize in Physics in 1987, opened a new world of opportunities for nuclear magnetic resonance (NMRs) and magnetic resonance imaging (MRIs) to move away from liquid cryogens. This discovery expands the application of high temperature superconducting (HTS) materials to fields beyond the chemical and medical industries, including electrical power grids, energy, and aerospace. The prototype 400-MHz cryofree HTS NMR spectrometer installed at Amgen's chemistry laboratory has been vital for a variety of applications such as structure analysis, reaction monitoring, and CASE-3D studies with RDCs. The spectrometer has been integrated with Amgen's chemistry and analytical workflows, providing pipeline project support in tandem with other Kinetic Analysis Platform technologies. The 400-MHz cryofree HTS NMR spectrometer, as the name implies, does not require liquid cryogens refills and has smaller footprint that facilitates installation into a chemistry laboratory fume hood, sharing the hood with a process chemistry reactor. Our evaluation of its performance for structural analysis with CASE-3D protocol and for reaction monitoring of Amgen's pipeline chemistry was successful. We envision that the HTS magnets would become part of the standard NMR and MRI spectrometers in the future. We believe that while the technology is being developed, there is room for all magnet options, including HTS, low temperature superconducting (LTS) magnets, and low field benchtop NMRs with permanent magnets, where utilization will be dependent on application type and costs.

Thermal runaway criterion as a basis for the protection of high-temperature superconductor magnets

High-temperature superconductor (HTS) based high-field magnet systems are essential for particle accelerators and fusion energy applications. Quench protection of such magnets is difficult owing to a slow quench propagation velocity in HTS. While in conventional NbTi and Nb3Sn-based magnets, a normal zone expands typically quickly, and the stored energy is dissipated across a large volume of the windings, a normal zone in an HTS magnet propagates slowly and, thus, can heat up quickly to high temperatures destroying the conductor. At the same time, growing experimental evidence suggests that HTS conductors can operate in a stable dissipative flux flow regime for a substantial range of operational currents before entering an irreversible thermal runaway. Therefore, a new protection paradigm for HTS magnets has emerged, aiming to prevent quenching, using advanced diagnostics to detect the dissipative regime onset. In the present paper, we propose a simple criterion for the thermal runaway in HTS conductors and calculate allowable temperature margins within which an HTS magnet can be operated safely. Outside of those temperature margins, a common quench integral approach may be used to estimate the upper boundary of the time margin for activating the protection system. We verify the applicability of our approach by comparing the calculated runaway conditions for a Bi-2223 conductor with the experimentally measured values. The thermal and time margins can define the quench protection system’s requirements for implementing the quench-avoiding protection paradigm.

3D electromagnetic modelling for high‐temperature superconducting dynamo flux pumps using T‐A formulation

AbstractA high‐temperature superconducting (HTS) dynamo flux pump can inject DC currents into closed‐loop HTS magnets without contact. It enables the realisation of current‐lead‐free or even through‐wall charging systems for high‐field applications such as nuclear magnetic resonance/magnetic resonance imaging (MRI) magnets, fusion reactors and accelerators. Researchers have proposed many simulation models to understand the working principle of HTS dynamos, few of which are in 3D because of converging problems. Therefore, the influences of many key 3D parameters in the HTS dynamo are scarcely reported. The authors propose an efficient 3D modelling method of the HTS dynamo based on the T‐A formulation. The rotating magnets are modelled by a ring‐shaped permanent magnet with space‐time‐variant remanent flux density to avoid moving meshes. This, together with the T‐A formulation, makes the 3D model efficient and universal. The accuracy of the model is verified by the experimental instantaneous and time‐integrated dynamic voltages. Using this model, the authors present systematic case studies to thoroughly explore the influences of the key parameters of a dynamo flux pump on the dynamic voltage and losses. The proposed modelling method and results could significantly benefit the design and optimisation of HTS dynamos for high‐field magnets.

Longitudinal Insulation Design of Hybrid Toroidal Magnet for 10 MJ High-Temperature Superconducting Magnetic Energy Storage

Longitudinal Insulation Design of Hybrid Toroidal Magnet for 10 MJ High-Temperature Superconducting Magnetic Energy Storage

A quench detection method for parallel co-wound HTS coils based on current redistribution

High-temperature superconducting (HTS) coated conductors (CCs) have become the preferred material for superconducting magnet applications due to their high engineering current density and high mechanical strength. However, due to the low quench zone propagation velocity of CCs, magnets wound with CCs suffer from severe quench risks. Therefore, a rapid, sensitive, and reliable quench detection method is crucial for the safe operation of such HTS magnets. In this paper, we propose a quench detection method based on current redistribution, in which two pieces of HTS CCs are soldered together at each end and insulated in the middle part, which are then parallel co-wound into a double-pancake coil. The two tightly coupled windings and low resistance joints form a very low inductance current loop, resulting in fast current redistribution between the two co-windings even at the inception of quench (with still low quench voltage). We deduced analytical solutions of the current redistribution process under different magnet operational scenarios, including constant current operation, charging and discharging, and proposed quench detection criteria. Corresponding quench tests were performed on a small scale co-wound HTS coil, and the results well verified the analytical solutions and the effectiveness of the quench detection method. Our work may be useful for lowering the risks in HTS magnet quench in various applications.

Design, Construction, and Operation of Liquid Nitrogen Cooled MHD Miniature Ship with No-insulation High Temperature Superconductor Magnet

Design, Construction, and Operation of Liquid Nitrogen Cooled MHD Miniature Ship with No-insulation High Temperature Superconductor Magnet

Development of the sorption-integrated adiabatic demagnetization refrigerator (ADR) without active heat switches

This study reports on the test results of a proof of concept sorption-integrated adiabatic demagnetization refrigerator (ADR) for sub-Kelvin cooling. The configuration of the cooler is primarily simplified by eliminating heat switches which require active control. The whole refrigerator apparatus is composed of the high temperature superconducting (HTS) magnet to magnetize the single crystal Gadolinium Gallium Garnet (GGG), and the 4He sorption cooler. Both the sorption cooler and the magnet are cooled by a 4 K two-stage Gifford-McMahon (G–M) cooler. The sorption cooler consists of a sorption pump filled with activated carbon of 13.9 g and a gravitiy-assisted-4He thermosiphon with volume of 5.0 cm3. The pressure inside the thermosiphon is controlled by changing the adsorption capacity of the sorption pump. The performance of the developed cooler is preliminarily evaluated by a single-shot test. The sorption cooler precools the 3 T-magnetized GGG from 4.40 K to 1.94 K by evaporating the liquid helium contained in the thermosiphon. When helium inside the thermosiphon is evacuated by the sorption pump, the magnetized GGG is thermally disconnected from the 4 K heat sink. Subsequently, the GGG is adiabatically demagnetized by discharging the HTS magnet and reaches temperature of 0.55 K. However, after demagnetization, the gas helium inside the cooling system is condensed by the GGG, consequently reducing its cooling capacity. Detailed experimental results are presented and discussed in the remainder of the paper.

A flux pump driven non-soldering closed-loop HTS magnet and its electromagnetic-thermal semi-analytical modelling method

We propose a new flux pump driven non-soldering closed-loop (NSCL) high temperature superconducting (HTS) magnet free of any soldering joints throughout the magnet for persistent current mode (PCM) operation. All the superconducting parts of the magnet are wound directly with HTS closed-loop ring split from an 8 mm REBCO tape using our new cutting scheme free of any soldering requirements. The magnet contains two single-pancake coils connected in series forming a closed circuit through two parallel bridge branches. Two thermal switches set on the two bridge branches control the on–off of the two bridges. A copper coil with iron core installed around one of the bridges is employed as the flux pump to drive the HTS magnet. An electromagnetic-thermal semi-analytical modelling method is proposed to analyse the pumping process by which the transport current in the magnet is calculated. The theoretical limit equation of the saturation current is improved as well. The proposed method can predict the current of the NSCL HTS magnet during the pumping process and provide results that are close to experiments. Experiments verify both the feasibility of the proposed flux pump driven NSCL HTS magnet and the modelling method. The results show that the NSCL HTS magnet works well in the PCM, which provides inspiration to the design of PCM operation of high field HTS magnets. The proposed modelling method also helps guide the design of different forms of HTS magnets and the flux pumps driving them.

Analysis of charging characteristics of a 500 MHz HTS-LTS series NMR magnet with an intra-layer no-insulation HTS layer-wound coil structure

The intra-layer no-insulation (LNI) layer-wound coil has the advantages of high spatial magnetic field homogeneity and a smaller number of joints, as well as the ability of self-protection during quench, which has great potential in making MRI or NMR superconducting magnet. In this paper, a 500 MHz NMR magnet connected in series by a high temperature superconducting (HTS) magnet and a low temperature superconducting (LTS) magnet was designed, fabricated, and tested at a low field for homogeneity, in which the HTS magnet is an LNI layer-wound coil structure. And a helical equivalent circuit model of the 500 MHz HTS-LTS NMR magnet coupled with the stacked homogenization T-A and mechanical model is established, which agrees with the experimental results. This paper provides a sufficient numerical analysis of the charging characteristics of the HTS-LTS series magnet, including magnetic field homogeneity, current distribution, loss distribution, screening current induced stress, etc. And this paper provides valuable insights into the ramping behavior of the HTS-LTS series magnet, which can be useful for practical charging experiments.

Self-protected high-temperature superconducting demonstrator magnet for particle detectors

A high temperature superconducting (HTS) demonstration coil has been developed in the frame of the Experimental Physics department Research and Development program at CERN The magnet extends the recent experimental demonstration of aluminium-stabilised HTS conductors and supports the development of future large scale detector magnets. The HTS magnet has five turns and an open bore diameter of 230 mm. Up to 30 K, the coil was measured to be fully superconducting across four central turns at 4.4 kA, the maximum available current of existing power supply. The central magnetic field is 0.113 T, the peak field on the conductor is 1.2 T and the coil has a stored magnetic energy of 0.1 kJ. A 3D-printed aluminium alloy (Al10SiMg) cylinder acts both as a stabiliser and a mechanical support for the superconductor. The resistivity of Al10SiMg was measured at cryogenic temperatures, and has a residual resistivity ratio of approximately 2.5. The ability to solder ReBCO tapes (a stack of four REBCO tapes, 4 mm wide, Fujikura) to Al10SiMg stabiliser, electroplated with copper and tin, forming a coil, is demonstrated using tin-lead solder at 188 ∘C. The HTS magnet was proven to be stable when superconductivity was broken locally using a thin-film heater. Despite voids in the solder joint between HTS and stabiliser, no degradation of the magnet’s performance was observed after 12 thermal cycles and locally quenching the magnet. A numerical model of the transient behaviour of solenoid with partially shorted turns is developed and validated against measurements. Our work experimentally and numerically validates that using an aluminium alloy as a stabiliser for HTS tapes can result in a stable, lightweight and transparent magnet.

A novel heater-triggered HTS semi-persistent current switch with high switching-off resistance

A semi-persistent current switch (semi-PCS) with a simple fabrication process, high switching-off resistance, and minimal power dissipation during operation is required to realize the semi-persistent mode in a high-temperature superconducting (HTS) magnet. In this study, a semi-PCS with high switching-off resistance was developed by optimizing the HTS tape structure in a heater-triggered semi-PCS. This optimization was achieved by selectively removing a portion of the conductive and superconducting layers on the surface and edges of the HTS tapes. The microstructure of the treated HTS tape was then analyzed. The resistance of the semi-PCS in a non-superconducting state was measured, and it was connected to an insulated coil for performance testing. To further evaluate its impact, an equivalent electrical circuit model was developed and used to predict the effect of the semi-PCS when applied to a larger superconducting coil. Furthermore, the study explored the impact of the excitation rates on the power dissipation and heat generation of the semi-PCS.

Modeling methodology for the transformer-rectifier flux pump considering electromagnetic and thermal coupling

High-temperature superconducting (HTS) magnets are promising in the application of high-intensity magnetic field. HTS flux pumps are devices that can charge closed HTS magnets without direct electrical contact. Simulation is an effective way to clarify the physical mechanism and provide further insight into the design of the device. In this work, we propose an accurate and efficient modeling methodology to simulate the transformer-rectifier HTS flux pump, which has considered electromagnetic and thermal coupling. The validity of the model has been verified by experimental results and theoretical calculations. The working characteristics of the HTS flux pump are investigated based on the proposed model, including DC bias component in the charging loop, the voltage recovery delay of the dynamic bridge and the temperature distribution in the dynamic bridge. The simulation results clearly depict working details of the device, in terms of electricity, magnetism and heat. The proposed model can serve as a powerful tool to design the HTS flux pump in practical applications.