Generation High Temperature Superconducting Research Articles

Economically optimized design point of high-field stellarator power-plant

High temperature superconductors (HTSs) expand the design space of stellarator power-plants (PPs) toward high magnetic fields B, enabling compact major radii R. The present paper scans the space of B, R and other design parameters, finding solutions that are promising from a physics and engineering standpoint, while minimizing the capital cost of the PP and the levelized cost of fusion electricity. Similarly, it identifies minimum-cost design points for next-step burning plasma stellarator experiments of fusion gain 1<Q<10 . The study assumes advanced stellarator configurations of reduced aspect ratio, heated by neutral beam injection. Plasma-facing, flowing liquid metal (LM) walls protect it from high heat and neutron fluxes. The study relies on analytical first-principle calculations, and established zero-dimensional (0D) empirical scaling laws. Power flows are illustrated by Sankey diagrams. Plasma operating contours are used to determine the reactor’s start-up path. Sensitivity analyses are conducted to identify the most critical reactor parameters within physics, engineering and costing, quantifying their influence on the economics of the PPs. Such 0D study suggests that the assumed next generation HTS, flowing LM walls, and advances in compact plasma configurations could lead to an ignited stellarator PP of aspect ratio A∼4 , R⩽4 m, B > 9 T, and normalized plasma pressure β∼5% which would minimize both the cost of electricity and capital cost while achieving a net electric power of about 1 GW.

Optimization of heating profile for superconductor joint performance made by resistive joule heating process

The long-term heating (>60 min) of second generation high temperature superconductor (2G HTS) tape-joints at temperatures above 200 °C leads to the continuous deterioration of their superconducting properties. Previously, we proposed a resistive Joule heating process with a short heating time (∼10 min) that exhibited beneficial critical current (Ic), retention percentages (84–99 %), and joint resistances (74–697 nΩ cm2) in four independent experiments.In this study, we investigated two heating rates and three tape-joint areas. The results show that for the samples with different tape joint areas, the critical current retention percentages (97–100 %) and uniformity of specific joint resistances (82–272 nΩ cm2) were significantly improved at a high heating rate of ∼30 °C/min. The sintering of silver nanoparticles and oxidation characteristics of the copper stabilizers were observed using transmission electron microscopy, scanning electron microscopy, and Raman spectroscopy to elucidate the effect of different heating profiles. This study opens new avenues for improving the quality of 2G HTS tape joint processes for ultrahigh magnetic field applications.

Fault current limiter based on high temperature superconductors

High Temperature Superconductors (HTS) made the Superconducting Fault Current Limiter (SFCL) a reality in power electric grids. Resistive SFCL, which is the subject of this article, is based on a unique property of superconductors to quench from a non-dissipative to a high dissipative state above a given current. SFCL is an attractive response to the poorly solved problem of fault currents in power electric grids and makes it possible to enhance the security and quality of electricity, something that matters more than ever. Liquid nitrogen cryogenics – which is possible thanks to HTS- makes the cryogenics user friendly. In-field SFCL operations confirm this. Second generation (2 G) HTS materials or Coated Conductors suit well to SFCL. Due to its high interest, SFCL has been the subject of a great deal of research and development. In terms of Technology Readiness Level (TRL) it reaches 8 with several in grid test experiences.Here a short history of SFCL is presented with a highlight about Curl 10, Ampacity and SuperOx devices. The two major locations in the grid are reported: grid coupling and feeder protection. The quench phenomena is described in a bit more detail before the basic design (length and cross section) is presented. The design is primarily thermal, considering two extreme operations: fault with very high prospective current (clear short-circuit) and fault with prospective current close to the minimum runaway current along the length. This operation is called the hot spot one. It is due to the intrinsic variation of the critical current along the length and to the low Normal Zone Propagation Velocity (NZPV). The cost of the superconducting conductor is given, showing no bottleneck for an economic development. All the more it is still possible to lower the cost with some developments. This article ends with two real advances presently underway: Current Flow Diverter (CFD) and Sapphire substrate superconducting 2 G tape. CFD aims to increase the NZPV, to still further secure the operation and to reduce the conductor cross section. The use of sapphire substrates allows to reduce significantly the length of the design.

A novel joint-less coil: promising unprecedented magnetic field stability to solve the persistent current mode issue in 2G-HTS magnet application

Closed coils fabricated using second generation high temperature superconducting (2G-HTS) coated conductors (CCs) are promising for superconducting magnets, which operating in persistent current mode (PCM) such as magnetic resonance imaging (MRI) and nuclear magnetic resonance (NMR) systems. However, the fabrication and application of superconducting joints for 2G-HTS CCs still pose a significant challenge. This paper reports a PCM joint-less 2G-HTS coil for capturing magnetic fields, which is called ‘Four Pancake Coil (FPC)’. A novel winding method was developed to form four pancake structure and effectively solved the closed-loop problem of 2G-HTS magnets. Meanwhile, the FPCs generated a 70.4 mT central magnetic field at 77 K and lasted for 57 d with a magnetic field drift rate of only 0.065 ppm h−1, which can satisfy the requirements of MRI magnets. In addition to the closed-loop characteristics of the FPC, the stacked magnet also provides expandability and ease of maintenance exchange. These advantages make it highly promising for the development of closed-loop 2G-HTS magnets.

Experimental investigation of axial tensile and fatigue behaviors of HTS round strands

For the development of high-temperature superconducting (HTS) magnet systems of future fusion devices, a novel HTS round strand based on a stacking structure was designed and manufactured using second generation (2G) HTS tapes. Different mechanical loads during operation can result in irreversible degradation of the strand. The axial tension and fatigue loads need particular attention. Therefore, it is important to investigate the electromechanical behavior of the round strand under various axial tension and cyclic loads. In this paper, the axial tensile and fatigue tests were conducted at 77 K, self-field. Taking 95% critical current (Ic) retention as the criterion, the results of the tensile tests revealed that the average tensile stress and strain were as high as 344 MPa and 0.47%, respectively. Fatigue characteristics were also investigated as a function of axial tensile stress. No significant performance degradation was observed up to 100,000 loading cycles with stress amplitudes ranging from 20 MPa to 200 MPa. Ic degradation occurs after 16,000 loading cycles with 380 MPa as the maximum stress. Furthermore, the microscopic defects of the round strand samples due to fabrication imperfections and mechanical loading were investigated using metallographic microscope and scanning electron microscope. These results presented in this paper are useful for comprehending and improving the mechanical behaviors of the strand in high-field and large-scale fusion magnet systems.

Current Flow Simulation of Assembled Conductors for Field Coils of Liquid Hydrogen-Cooled High-Temperature Superconducting Generator

High-temperature superconducting (HTS) generators that functions in combination with a hydrogen gas turbine have the potential to reduce CO2 emissions in Japan. The system can realize zero-emission power generation, and it requires no refrigerator and has almost no cooling costs by fully using the cold energy of liquid hydrogen. The ultimate goal is to commercialize a 600 MW-class liquid hydrogen-cooled HTS generator that requires a 6 kA-class assembled conductor with an outer diameter of approximately 6 mm that can conduct 6 kA at 20 K and 5 T. A technical challenge in applying assembled conductors to the field coils of generators is realizing the interlayer current distribution during steady-state operation and quick-response excitation. A conductor with four layers of 12 wires wound on a 5 mm-diameter former was experimentally and numerically studied, and the current distribution was examined. Similar waveforms were numerically obtained when the terminal resistance of each layer was set to 5/90/60/40 nΩ/m. Such variations in the terminal resistance have a slight effect on the transport characteristics of long conductors.

Operation of Prototype Race-Track Closed-Loop HTS Coil With Metal-as-Insulation in Solid Nitrogen

The second generation (2G) high temperature superconductor (HTS) has excellent current-carrying density performance in strong magnetic field. Thus, the maglev system driven by 2G HTS magnets has been studied a lot. In the design of magnets, metal-as-insulation coil retains self-protection feature of the no-insulation coil, and it performs well in charging time. On the other hand, using solid nitrogen (SN <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> ) as a “thermal battery” may effectively reduce the volume of on-board HTS magnets. In order to design on-board magnets with fast charging, small volume and self-protection, firstly a prototype coil was manufactured. Then the experiment apparatus was set up and experiments in the persistent current mode were carried out. It was obtained by fitting that the magnetic field decay rate of the prototype coil was about 0.24% per day. This paper provides a foundation for the production of real-scale on-board magnets cooled by SN <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> .

Design Study of an HTS Linear Power Generator Suitable for Wave Energy Converter

In this paper, we show a conceptual structure of a direct drive linear power generator with REBaCuO high-temperature superconducting (HTS) bulk field poles for wave energy conversion. The proposed linear power generator structure is comprised of a moving armature coil and HTS bulks concept, which we call it a dual translator power generation system. Its performance has been analyzed using a finite-element electromagnetic field analysis method. A determination of the main machine parameters for the dual translator HTS linear power generator was conducted. Simulation results were compared between our dual translator HTS linear generator structure and the use of permanent magnets (PMs) for the field poles of that structure. It was found that the electromotive forces, electromagnetic forces and output power of the dual translator HTS linear power generator structure are 1.67, 2.63 and 2.60 times superior to that of dual translator PM linear generator structure, respectively. A combination of the dual translator power generation system and HTS bulks has the potential to help us to achieve higher torque and higher output power despite low ocean wave speed, which is important to achieve practical application of ocean power generation systems.

Influence of Interturn Contact Stress on the Quench Behavior of Insulated YBCO Pancake Magnets: A Study Based on Numerical Simulations

Insulated high temperature superconducting (HTS) magnets are still widely used in low field applications, such as HTS motors and generators. In this paper, a two-dimensional/three-dimensional (2D/3D) mixed electrothermal model and a homogeneous 3D electrothermal model are employed to study the influence of inter-turn contact stress on the minimum quench energy (MQE), longitudinal and transverse normal zone propagation velocity (NZPV) of insulated YBCO magnets for the temperature range 30 K – 60 K. This temperature range is of interest usually in applications, such as HTS motors, generators and transformers, because it allows the use of low cost cooling system. It is found that MQE increases significantly with increasing inter-turn contact stress. The inter-turn contact stress has small influence on the longitudinal NZPV of insulated YBCO pancake magnet. However, the transverse NZPV rises significantly with the increase of inter-turn contact stress. The transverse NZPV is nearly proportional to the inter-turn contact stress. The 3D homogeneous model gives results that are in agreement with those of 2D/3D mixed model, especially for the temperature range 45 K – 60 K; however, the MQE and transverse NZPV given by the two models are different for the temperature range 30 K – 45 K. That means for insulated HTS YBCO pancake magnets operating at the temperature range 45 K – 60 K, the 3D homogeneous electro-thermal model can be a good replacement of the 2D/3D mixed model to study the quench behavior, which can achieve better computational efficiency without significant loss of accuracy.

An Improved Critical Current Calculation Method of HTS Field-Excitation Coil for Double-Stator HTS Generator With Stationary Seal

In this article, a calculation method for critical current of high-temperature superconducting (HTS) excitation coils made by Bi-2223 tapes is proposed, which can provide a reference for the design and manufacture of HTS excitation coils. Based on the test data provided by the manufacturer, the suppression effect of the applied parallel and perpendicular magnetic field on the critical current density is separately described by the proposed Jc-B model of the Bi-2223 tapes. Then, taking a 10 kW double-stator HTS machine (DS-HTSM) as an example, the target excitation magnetomotive force (MMF) required to meet its designed electromagnetic properties is obtained. After then, the turns number and the critical current of the HTS excitation coils required to meet the target MMF are calculated by the finite element analysis (FEA). Further, the FEA model of the DS-HTSM will be built by using the homogenization modeling method of HTS coils, and the influence of the armature reaction magnetic field on the critical current of the HTS excitation coils is analyzed. Finally, the correctness and effectiveness of the proposed improved critical current calculation method is verified by fabricating the 10 kW DS-HTSM prototype and conducting experimental test.

Accurate sub-domain model for magnetic field computation in electrical machines with HTS materials

The primary aim of this study was to develop and validate an accurate sub-domain analytical model to estimate the magnetic field of electric machines with high-temperature superconducting (HTS) excitation and armature windings. The model was developed by utilizing the separation variable and harmonic analysis methods to solve Laplace’s or Poisson’s equations of the vector magnetic potential in two-dimensional polar coordinates. The theoretical derivations of the final analytical equations for the magnetic flux density distribution in the air-gap and in permanent magnets, electromagnetic torque, and no-load back-electromotive force (back-EMF) are explained in detail. Finally, the magnetic vector potential, flux density distribution of each sub-domain, no-load back-EMF, and inductive reactance of the armature winding were solved by considering the critical parameters of the superconducting materials, and the influence of higher harmonics. The finite-element method (FEM) was used to validate the accuracy of the developed analytical method for the investigated HTS generator. The results show the developed analytical method is accurate and time-saving.

Conceptual design, AC loss calculation, and optimization of an airborne fully high temperature superconducting generator

With the trend of multi-electrification and hybrid-electrification of aircraft, the airborne high temperature superconducting (HTS) generator is considered as the key technology of the new generation of aviation power generation system and has received wide attention. The high critical current and low loss of superconductors can significantly improve the output power, power density, efficiency and other performance of generators. In this work, conceptual design of a fully HTS generator for aircraft is carried out to address key issues in terms of AC loss distribution, which serves as the ground of cryogenic design in the future. A 10 MW fully superconducting generator is designed to be used in a large passenger aircraft (with more than 150 seats and a maximum takeoff weight of about 100 tons). Based on the finite element method (FEM) with the so-called T-A formulation, the electromagnetic characteristics of the generator are analyzed, and AC losses of the stator and rotor are calculated. To calculate the rotor loss in realistic dynamic-field environment, a technique named “rotation-domain exchange” is developed and implemented. By using such technique, accurate calculation of AC loss of the rotor in realistic dynamic electromagnetic environment is achieved with no need of simplified boundary condition as previously reported work. Based on the model, the stator coil structure is optimized to reduce the AC loss and the rotor coil structure is optimized to reduce the HTS tape usage. Results show that the optimized stator AC loss is 15.645 kW, and the rotor AC loss is 6.268 kW, indicating that the rotor AC loss of a fully superconducting generator with narrow air gap and large number of coil turns is not neglectable as previous work assumed. Thus, precise calculation and dedicated optimization of the rotor loss is critical since cooling of the rotor is much more challenging than the stator as the former remains in motion.

Defect Evolution in Y&lt;sub&gt;0.5&lt;/sub&gt;Gd&lt;sub&gt;0.5&lt;/sub&gt;Ba&lt;sub&gt;2&lt;/sub&gt;Cu&lt;sub&gt;3&lt;/sub&gt;O&lt;sub&gt;7-&lt;/sub&gt;&lt;sub&gt;δ&lt;/sub&gt; Layer by H Ion Irradiation

In order to further improve the superconducting current carrying capacity of REBCO coated conductor under strong magnetic field, ion irradiation is used to generate the pinning center of introduced magnetic flux in the REBCO coated conductor. In this paper, the H-ion irradiation of REBCO second generation high temperature superconductor strip was carried out by using the 320kV high charge state ion synthesis research platform. DB-SPBA combined with Raman spectroscopy was used to measure the change of microstructure in YBCO samples irradiated by H+ions within the range of 5.0×10&lt;sup&gt;14&lt;/sup&gt;~1.0×10&lt;sup&gt;16&lt;/sup&gt;. The positron annihilation parameters in YBCO before and after irradiation were analyzed. It is found that after 100 keV H+ion irradiation, a large number of defects including vacancy, vacancy group or dislocation group are produced in the superconducting layer. The larger the irradiation dose, the more vacancy type defects are produced, the more complex the defect types are, and the annihilation mechanism of positrons in the defects changes. Raman spectroscopy results show that with the increase of H+ion irradiation dose, the oxygen atoms in the coating rearrange, the plane spacing increases, the orthogonal phase structure of the coating is destroyed, and the degree of order decreases. The defects produced by such ion irradiation lay a foundation for the introduction of flux pinning centers. Further research can be carried out in combination with X-ray diffractometer, transmission electron microscope, superconductivity and other testing methods to provide theoretical and practical reference for the optimization of material properties.

Edge cracking behavior of Y2O3 coatings by the solution deposition planarization method

As an efficient flattening technique for surface smoothing, solution deposition planarization (SDP) has recently drawn more attention as a fabrication method for second generation high temperature superconducting (2G-HTS) tapes. However, at present, it is still challenging to achieve edge crack-free surfaces while preparing a Y2O3 coating via SDP processing, especially during drying and heat treatment. Experimental results show that as the colloidal dispersion is coated and dried on a nonporous rigid substrate, the enormous stresses developed during the drying process can fracture the thin film. The finite element simulation results show that coating thickness, which is affected by the differences in pulling rate and solution concentration, is a critical factor determining the crack sies may be initiated. After optimizing the coating parameters, a 10-m long Hastelloy C-276 alloy base was successfully prepared. The average value of Ra was 1.28 nm, which is less than 5 nm (5 × 5 μm2), satisfying the industrial requirements for the preparation of superconducting materials using the IBAD (lon Beam Assisted Deposition) technology route.

Current redistribution during inhomogeneous quench of 2G HTS tapes

Inhomogeneous temperature elevations, also called hot spots, occurring in second generation high-temperature superconductor (2G HTS) tapes may lead to their destruction. A better understanding of inhomogeneous quenches would contribute to develop strategies to better protect superconducting devices based on 2G HTS tapes against hot spots. To do so, we investigated the current redistribution around a dissipative zone in a 2G HTS tape with a combination of experiments and numerical simulations based on the finite element method (FEM). Firstly, the inhomogeneous heat generation in a commercial 2G HTS bare tape (without copper cladding) was observed through the visualization of bubble generation. Secondly, the current redistribution around a dissipative zone in commercial 2G HTS bare tapes from two different manufacturers was investigated using voltage taps on both sides of the tape. The measured voltages showed that the current redistribution around the dissipative area in the top stabilizer layer of the tape is different from that in the bottom stabilizer layer. Using a 3D electro-thermal FEM model, we reproduced these behaviors, assuming a HTS tape architecture with an inhomogeneous local critical current density. Finally, using the same FEM model, we explored the impact of a lack of silver on one lateral side of a 2G HTS tape. Our results indicate that such a lack of silver does not critically affect the quench dynamics.

Characteristics of the Superconducting Field Winding of an HTS Wind Turbine Generator During a Short Circuit Fault

High temperature superconducting generators (HTSGs) have great potential of high power density for future large direct-drive wind turbines. As synchronous machines, HTSGs have rapid rise of field currents during a sudden short circuit fault which cause AC losses in the HTS tapes. This paper applies <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">H-A</i> formulation of Maxwell equations for finite element simulation of electromagnetic behavior of a 10 MW, 9.6 rpm HTSGs. The model is integrated to a short circuit model to calculate the characteristics of the HTS field winding, such as field currents and AC losses during a three-phase no-load short circuit fault at the armature winding terminal. Two HTSG designs are compared. The <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$n$</tex-math></inline-formula> value characterizing the sharpness of the superconducting-resistive state transition of the HTS tape and the number of armature winding segments are analyzed as key variables. The result indicates high AC losses are produced but more armature winding segments can effectively reduce the AC loss and the field current. A lower <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$n$</tex-math></inline-formula> value can also lower the AC loss level but only for the non-magnetic rotor design. The field current is not affected by the <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$n$</tex-math></inline-formula> value for both HTSG designs.

Microplastic Collection With Ultra-High Magnetic Field Magnet by Magnetic Separation

In recent years, the increase of microplastics (MPs) in ocean have been recognized as one of ocean pollution listed in Sustainable Development Goals (SDGs). Since MPs absorb harmful chemicals while floating in ocean, small fish which eats the absorbed MPs may fall into bad digestion and poor health condition. To solve the ocean pollution problem, a good MP collection method must be proposed with a high processing speed and a high MP collection ability. While, recently, the performances of 2nd generation high-temperature superconducting (HTS) magnets which can generate a field higher than 15 T have been improved. It is expected that MP collection performances are enhanced with such high field superconducting magnets. In this paper, we propose a conceptual design for MP collector from seawater using superconducting magnets. To evaluate the performances of the device, we developed a fluid simulation coupled with magnetic field simulation. The simulation results indicate that MPs can effectively be collected with a high magnetic field with a high processing speed.

Lamination process of second generation high temperature superconducting tape at Shanghai Superconductor Technology

As the second generation high temperature superconducting (HTS) tape enters the stage of commercialization and mass production, it has been successfully applied in several power and magnet devices. Different application scenarios also put forward different requirements for the electrical and mechanical properties of the HTS tape. This paper focuses on introducing the post-processing treatments of HTS tape, primarily copper plating and lamination. By preparing typical samples, the properties of copper-plated tapes and laminated tapes have been experimentally compared. The results show that under the condition of sufficient liquid nitrogen flow, the steady-state over-current tolerance of copper-laminated tape is significantly better than that of stainless steel-laminated and copper-plated tapes. At the same room temperature resistance, the over-current impact tolerance of stainless steel-laminated tape is 2–3 times that of copper-plated tape; the maximum transient current beared by the tapes reached 3896 A when they were put under shock for 8 ms, which has significant advantages in the application of resistive fault current limiter. At 77 K, yield strength Rp0.2 of the three types of superconducting tapes are > 1100 MPa for stainless steel-laminated tape, 645–1037 MPa for copper-plated tape and < 500 MPa for copper-laminated tape. The critical tensile stress of stainless steel laminated-tape is higher than that of copper-plated tape and copper-laminated tape. The tape reinforced structure described in this paper can provide a helpful reference for future design and manufacture of superconducting applications in power and magnet industries.

An efficient approach for superconducting joint of YBCO coated conductors

Superconducting joints are crucial for second generation high-temperature superconducting (2G HTS) closed-loop coils that work in the persistent current mode (PCM) operation. Here, we report an efficient approach for superconducting joints of YBa2Cu3O7-σ (YBCO) coated conductors (CCs). The YBCO layer is etched to and from some microchannels, which serve as oxygen diffusion paths during oxygenation annealing (OA), to accelerate the recovery of critical current (I c) of the joined two YBCO layers. The I c of the superconducting joint is 118 A at 77 K with an optimized joining temperature and a short OA time (10 h), which is about 82% I c of the joined YBCO CCs. The persistent field decay of the closed-loop coil shows a joint resistance (R j) of less than 2.2 × 10−13 Ω at 77 K. Two YBCO films epitaxially grown along the c-axis diffuse into each other at the interface and form a dense joining, enabling superconducting current path. This superconducting joint technique can promote the achievement of the PCM operation in 2G HTS magnet applications, such as magnetic resonance imaging and nuclear magnetic resonance.

Thrust estimation for HTS-magnet based Magneto Plasma Dynamic Thrusters (MPDT)

At present time, electric propulsion is being considered for outer deep space missions. Magneto Plasma Dynamic Thrusters are capable of accelerating semi- neutral plasma gas (Xenon, Iodine, Argon, Ammonia, or Lithium) to a high exhaust velocity using combination of RF power & high magnetic fields. High Temperature Superconducting (HTS) coils can generate high magnetic field due to high operating current density at temperatures below its critical temperature(Tc). These superconducting coils can be cooled by using the cold of outer dark space. The use of 2nd Generation (2G) HTS coils can increase thrust, by increasing high magnetic field with very low power consumption. Thus, specific impulse due to the combination of RF plasma and HTS based superconducting high magnetic field is increased drastically. In this paper, the thrust calculation are carried out for MPDT for varying magnetic fields produced by superconducting coils. The estimation of exhaust velocity and thrust generated by plasma for an MPDT is of great challenge and is required to determine for calculating the life of mission as well as the distance of travel. These estimations are required to support the indigenous development of MPDT.