Large Current Capacity Research Articles

Superconducting surface trap chips for microwave-driven trapped ions

Microwave-driven trapped ion logic gates offer a promising avenue for advancing beyond laser-based logic operations. In future microwave-based operations, however, the joule heat produced by large microwave currents flowing through narrow microwave electrodes would potentially hinder improvements in gate speed and fidelity. Moreover, scalability, particularly in cryogenic trapped ion systems, is impeded by the excessive joule heat. To address these challenges, we present a novel approach: superconducting surface trap chips that integrate high-Q microwave resonators with large current capacities. Utilizing sub-ampere microwave currents in superconducting Nb resonators, we generate substantial magnetic field gradients with significantly reduced losses compared to conventional metal chips. By harnessing the high Q factors of superconducting resonators, we propose a power-efficient two-qubit gate scheme capable of achieving a sub-milliwatt external microwave input power at a gate Rabi frequency of 1 kHz.

The dynamic resistance of muti-layer conductor on round core cables for SMES systems

The conductor on round core (CORC) cables with multi-layer structure show great potential for superconducting magnetic energy storage (SMES) because of their low AC losses and large current carrying capacity. The dynamic resistance is an important electro-magnetic property of CORC cables for SMES. Considering that experimental results of multi-layer CORC cables are usually difficult to obtained, numerical model is an efficient method to demonstrate their electro-magnetic properties. In the work, a numerical model is proposed to illustrate the dynamic resistance of the multi-layer CORC cables. Then, an analytical model using method of rotating magnetic field is proposed to provide mathematical expressions for computing the dynamic resistance, which verifies the numerical model. According to the numerical model, the impacts of DC current and AC magnetic field on dynamic resistances of the multi-layer CORC cables are investigated respectively. The simulation clearly illustrates the dynamic resistance characteristics of CORC cables, showing dynamic resistances and currents in individual layers. This study can serve as a valuable guidance for the implementation of multi-layer CORC cables in SMES systems.

Magnetization Loss Measurement of Twisted Stacked Tape Cable and Comparison With CORC

High Temperature Superconducting (HTS) cables for large current capacity are being studied in several forms for power device applications. Currently, the cables are being developed for DC applications rather than AC applications. However, if a technology for reducing AC loss is developed, it will be possible to apply HTS cables to various AC devices. Twisted Stacked-Tape Cable (TSTC) is one of the large current HTS cables. It is made by stacking and twisting multiple HTS tapes for large current capacity. The HTS tapes in TSTC should be twisted for the uniformity of current distribution in each tape. Since the HTS tape has a wide thin film shape, it is very difficult to twist itself. In this paper, we measured the magnetization losses of TSTC samples without the striations under AC magnetic fields that had peak values below 0.1 T. Several molds for the TSTC samples were made by using a 3D printer. TSTC samples had several numbers of stacked tapes and two kinds of the tape width. The magnetization losses of the samples in the molds were measured under uniform AC magnetic fields. The experimental results were compared to those of the straight HTS stacked cables and conductor on round core (CORC) cables.

Current Sharing Among Transposed Three-Parallel REBa2Cu3O y Tapes in Single-Phase Armature Coils

To realize a large current capacity in REBa <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> Cu <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> O <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">_y</i> superconducting coils, we have proposed a cabling design for the transposed multi-strand parallel conductors. This cabling design is also useful for a superconducting armature coil in a fully superconducting rotating machine system. Very recently, we developed an analytical method based on simple modeling, to roughly calculate the current distributions among the continuous strands in rotating machine conditions. In this manuscript, the current distributions predicted by the analytical method were compared with the measured values. Further, to understand the complex current distribution property for the three-strand parallel conductors, the turn number dependence of the current distribution with various transposition combinations was investigated. The current branches were measured under liquid nitrogen temperature of 77.3 K by Rogowski coils by applying AC transport current. The analytical method described the complex current distribution of the strands well, especially the coil with a large number of turns.

Development of a Compact HTS-FAIR Conductor for Magnet Application

Research and development of large-current capacity high temperature superconducting (HTS) conductors for magnet applications in nuclear fusion experimental devices is underway in the world. As a candidate conductor, the FAIR conductor has been developed, in which REBCO tapes and pure aluminum sheets are alternately stacked in an aluminum jacket, and the lid is covered by friction stir welding (FSW) method. Producing several prototypes of FAIR conductors, current transport tests have been repeatedly conducted in liquid nitrogen without an external magnetic field to optimize the manufacturing process of the conductor. In addition, we have also investigated the properties of the conductors in low temperature under high magnetic fields. As the next step, we have been planning to conduct coil shape tests in high magnetic fields. For installation in a test facility, we have developed a reduced diameter FAIR conductor from 12 mm to 6 mm. 1.5 rotations/m reduced version of FAIR was fabricated and current transport tested in 77 K, self-magnetic field. Compared with the results of critical current analysis considering the self-magnetic field, the retention of <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">I</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">c</sub> was 67%. After cutting the fabricated the compact FAIR conductor and observing the inside, it was found that the REBCO tapes were folded by FSW. Therefore, it was found that further optimization of the FSW process was necessary.

Interfacial chemistry regulation via dibenzenesulfonamide-functionalized additives enables high-performance Zn metal anodes

Zinc metal with high safety and low cost is considered as a promising anode for rechargeable aqueous batteries, yet its application suffers from the serious dendrite formation and spontaneous corrosion. Here, we report a novel additive design principle to boost highly reversible and dendrite-free zinc anode, via introducing Dibenzenesulfonamide (BBI) into typical ZnSO4 electrolyte. Finding confirms that the formed BBI-derivate is preferentially chemisorbed on Zn surface over solvated H2O to protect Zn-electrode against corrosion effect and suppress hydroxide sulfate formation, and simultaneously contributes to desolvation process of Zn(H2O)62+. More encouragingly, a robust organic-inorganic hybrid solid electrolyte interphase on Zn anode with a hydrophobic ability is in-situ constructed due to the decomposition of BBI, which further regulates Zn-anode interfacial chemistry to favor Zn homogeneous deposition effectively. Consequently, the Zn symmetric cells deliver an extended cycling lifespan of 5000 h (0.5 mA cm−2/0.5 mAh cm−2), and ultrahigh cumulative capacity of 10.6 Ah cm−2 at concurrently large current density and high areal capacity (10 mA cm−2/10 mAh cm−2). This study clearly elucidates the multiple interface-mediated behaviors to stabilize Zn anode, which contributes to a deep insight into the additive regulation mechanisms and brings a promising approach to solve the anode nuisance in aqueous metal batteries.

Highly reversible, dendrite-free and low-polarization Zn metal anodes enabled by a thin SnO2layer for aqueous Zn-ion batteries

Dendrite-free Zn anodes protected by a zincophilic, hydrophilic and thin (∼100 nm) SnO2layer exhibited an outstanding electrochemical performance over a wide range of cycling, especially for Zn plating/stripping with large current and high capacity.

Highly extendable passive current balancing interleaved high step‐up boost converter using voltage multipliers

AbstractHigh step‐up boost converters with large input current capacity are necessary for low‐voltage renewable energy sources, such as photovoltaic panels and fuel cells. Interleaved converters are a suitable topology for low‐voltage, large input current applications. Conventional interleaved converters, however, face a variety of challenges, such as the necessity of additional current control loops for active current balancing, increased voltage stress of semiconductors, and poor extendibility. In this paper, highly extendable interleaved high step‐up boost converters with a passive current balancing and reduced semiconductor voltage stresses are proposed. Current capacities and step‐up conversion ratios of the proposed converters can be arbitrarily enhanced by extending the number of phases and voltage multiplier (VM) stages, respectively. The experimental results of 500‐W prototypes demonstrated passive current balancing, reduced semiconductor voltage stresses, and enhanced step‐up conversion ratios.

Investigating the effect of transverse compressive loads on the electromagnetic performance of superconducting CORC® cables

High-temperature superconductor (Re)Ba2Cu3O x (ReBCO) conductor on round core cable (CORC®) has a large current carrying capacity for high field magnets. Lorentz forces acting on CORC conductors, cause a reduction of the critical current, or even permanent degradation of their performance when exceeding critical values. Transverse compressive stress is one of the principal mechanical stresses when CORC cables are bundled to cable-in-conduit conductors (CICC) conductors capable of operating at currents up to 100 kA in magnetic fields of up to 20 T. In this research, a mechanical-electromagnetic model is developed to study the effect of transverse compressive loads on the electromagnetic performance of CORC cables. A mechanical transverse load on the cable is implemented to simulate the electromagnetic force. A comparison of numerical simulations with experiments for a three-layer CORC cable is first performed to validate the model’s reliability, with particular attention to critical current reduction during the transverse compression process. A novel feature of this paper is that the model developed can analyze both mechanical response under transverse compressive loads and electromagnetic performance under applied AC magnetic fields with low amplitudes. On this basis, the model investigates the effects of winding parameters on the axial strain and critical current reduction of the ReBCO layer in a single-layer CORC cable. The numerical analysis shows that increasing the winding angle can reduce the axial strain and critical current reduction of the ReBCO layer in the contact area. Subsequently, a detailed comparative study is carried out studying the axial strain of the ReBCO layer in the non-contact area with and without taking the winding core into account. In addition, a sudden increase in the magnetization loss is explained when the transverse compressive load reaches a certain level. Finally, a six-layer CORC cable’s electromagnetic analysis is performed, and each tape layer’s critical current reduction is investigated and discussed. The comparison of magnetization loss and current density between six- and single-layer CORC cables in the no-strain case is also given. This finite element model can guide optimizing a cable design for specific application conditions.

Magnetic Field Distribution and Ripple Loss Analysis of an Optimized Self-Shielding DC HTS Cable

Compared with AC HTS cable, DC high-temperature superconducting (HTS) cable has prominent advantages of low transmission loss, large current capacity and high controllability. The current directions in adjacent layers of “sandwich” cable with self-shielding characteristic are opposite, which can greatly reduce the magnetic field influence and the critical current degradation. In order to homogenize the magnetic field distribution of the cable, an optimized self-shielding DC HTS cable is proposed. Compared with the previous structure, the optimized self-shielding DC HTS cable has a larger critical current and smaller ripple loss. In this paper, the magnetic field distribution and the ripple loss of three different DC HTS cables with ripple current are studied by a two-dimensional (2D) finite element method (FEM) based on T-A formulation. The 2D simulation model offers a valuable reference for the design and operation of DC HTS cable with low voltage and large current.

Magnetization Loss of Multi-Layered CORC According to Various Winding Types

Conductor on round core (CORC) is one of high temperature superconducting (HTS) conductors with large current capacity. CORC stacks HTS tapes to increase the current capacity. CORC can have various structures according to how we stack HTS tapes. The direction of the spiral winding in each layer and the overlapped area of HTS tapes affect AC losses of CORC because the losses mainly depend on the perpendicular magnetic fields on the HTS tapes. We have measured the magnetization losses of CORC short samples with various structures. Each sample has a different number of layers, winding direction in each layer, and overlapped area. We confirmed the best structure of CORC with the least magnetization loss.

Influence of Dynamic Resistance on Current Distribution of HTS DC Cable Conductor for Feeder Lines and Large Scale Magnet

HTS DC cable conductors are promising because of high current density and intrinsic zero resistance. Therefore, HTS cable conductor with large current carrying capacity are expected to have widespread application in feeder lines and large scale magnets. At present, the conventional design of HTS cable conductor, general several of 10 kA, are designed with goal of uniform current distribution by adjusting winding pitch same as AC HTS cable since the ripple current is unavoidable in DC transmission line and AC current in process of exciting and demagnetizing is also alternative. Thus, AC magnetic field component generated on tapes of HTS cable conductor is non-negligible. If the AC magnetic field component is higher than the penetration field of the HTS tapes, there is inevitable dynamic resistance among them. Dynamic resistance is seldom considered in previously conventional design of DC cable conductors. The dynamic resistance significantly affects the current distribution among HTS tapes except for generating extra loss and incurring instability. Based on the conventional design method of uniform current, this paper presents the DC current distribution among layers by considering dynamic resistance, which is particularly much more significant for large current capacity HTS DC cable conductors with ripple currents.

Demonstration of kA-Class Rutherford Cables Using MgB2 Wires for an Energy Storage Device Suitable for a Liquid Hydrogen Indirect Cooling

Superconducting Magnetic Energy Storage (SMES) has been a promising option amongst potential other storage devices to support world-wide demands for introducing more renewables into the utility grid. If MgB <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> strands are used for SMES, liquid hydrogen, one of the renewables, could be used not only as a clean energy source but also as a coolant for the superconducting device. For large-scale coil design, mechanically fragile multi-filament strands should be used for their low AC loss feature considering that the transport current inside the coil would be always changing. To realize such a design, we designed and fabricated the large current capacity for AC-use Rutherford cable, together with experimental tests for its feasibility assessment. Based on the latest test results and development of commercial MgB <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> strands with high mechanical strength, and this research and development of kA-class cable at liquid helium temperature for extrapolating the critical current ( <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">I_c</i> ) at hydrogen temperature, we believe this approach has the potential to make a practical SMES device with MJ capacity. In this paper, the world's largest-capacity AC cable design and test results including critical current evaluation under several background field strengths are shown, and the stability and current re-distribution are also discussed.

Novel GIS Mechanical Defect Simulation and Detection Method Based on Large Current Excitation With Variable Frequency

The mechanical defects of gas-insulated switchgear (GIS) equipments seriously threaten their safe and stable operation, but there are detection problems such as latency and weak vibration response, especially for high-capacity GIS with large size. In this paper, a novel GIS mechanical defect simulation and detection method based on large current excitation with variable frequency is proposed to solve this problem. First, a 500 kV GIS mechanical defect simulation and detection system with variable frequency and large current loading capacity was designed by structural parameter adjustment, power matching and harmonic suppression based on the nonlinear vibration mechanism. Then, the vibration characteristics of normal and typical defects of GIS equipment with different excitation frequencies were experimentally studied. Finally, the evolution laws of vibration signals and features for mechanical defects with different severity levels at different currents were explored, and a defect identification model for different load intervals was established. Results show that the amplitude growth and superharmonic point frequencies of vibration signals are related to the defect types and excitation current frequencies. The nonlinear vibration signal features such as kurtosis and gravity center frequency of defective equipment are more significant when using the proposed detection method compared with single frequency excitation, especially at large currents above 3,000 A, which not only makes it easier to find internal defects at an early stage but also helps to overcome the missing detection problem of the traditional method, and the defect recognition accuracy based on vibration signals of variable frequency excitation is higher.

Full‐Scale Large Eddy Simulation of a 185 t Ladle Optimizing a Hybrid Eulerian Grid and a Discrete Bubble Mapping Approach

Numerical simulation is a vital tool for the continuous improvement of all steelmaking processes. In previous works, the authors have dedicated different approaches to optimize modeling of fluid flow in the ladle. This includes a sensitivity analysis of validation techniques, assembling of a validation database, and a model optimization on the water model scale. Herein, the final part of this project is presented at which the optimized model is scaled to the real process. Associated problems are identified and solutions are proposed. To achieve a tradeoff between large eddy simulation (LES) grid requirements and current computational capacities, a hybrid meshing strategy is optimized. To overcome the intrinsic drawbacks of the Euler–Lagrange model, a mapping approach for phase decoupling is implemented and made publicly available on GitHub. The upscaling of semi‐empiric submodels is discussed. Good agreement with experimental mixing time measurements is found, indicating the success of upscaling. A first time‐averaged flow field of a full‐scale 185 t ladle with the LES model is presented. Due to the extreme computing requirements, these results may currently be used as a benchmark, but the trend toward increasing computing capacities may make LES models state of the art in the future.

Study on Structure Type and Operation Condition of UHVDC Wall Bushing

When the ±800kV UHVDC capacity is increased to 10000MW, the transmission current is 5kA and 6.25kA, which will put forward new requirements for the key technology of UHVDC through wall bushing: in UHV level, the key of through wall bushing lies in the research of basic technology of voltage sharing and field sharing. In the case of large current carrying capacity, the key lies in the basic technology research of current sharing and heat sharing. When the DC wall bushing, converter bushing and outgoing line device operate at the rated voltage, the central conductor is heated due to the carrying large DC current. Therefore, the temperature field distribution inside and at the tail of the bushing core is uneven, and the resistivity is the function of temperature, resulting in the change of resistivity with temperature and the change of potential and electric field distribution with resistivity during operation. Therefore, under the above high current operation conditions, in-depth key technology research is required for the design of bushing current carrying device, calculation of internal potential and electric field distribution, voltage sharing, field sharing, current sharing and heat sharing technology. The combined action of electrical and thermal stress will significantly affect the internal electric field distribution of converter transformer core and accelerate the aging rate of core composite insulation material, which introduces new research topic for the key technology of UHVDC converter bushing. The electric field and voltage distribution of UHVDC bushing are theoretically analyzed, the insulation structure is optimized from the aspects of material and structure, and the manufacturing process and the test technology are deeply and systematically studied.

Superconducting joining of YBCO coated conductors without a large critical current loss

Achieving superconducting joinings with large current capacities is a challenge for magnetic resonance imaging applications of YBa2Cu3O7-δ (YBCO) coated conductors (CCs). Here we report a novel method to fabricate a superconducting joining between two YBCO CCs using a joining strap consisting of YBCO, Ag, a buffer, and a substrate. The YBCO layer exfoliated from the buffer stack of a YBCO CC can retain more than 90% of its original critical current (Ic). This is particularly due to the Ag layer serving as a fast oxygen diffusion path to promote the recovery of superconductivity of the YBCO layer during oxygenation annealing. The atomic arrangement at the joined YBCO interface is well aligned along the (001) plane, enabling superior superconducting performance. The method reported here provides a practicable solution to achieve persistent current mode operation in second-generation high-temperature superconducting magnet applications.

Improvement of Ic degradation of HTS Conductor (FAIR Conductor) and FAIR Coil Structure for Fusion Device

As a high-temperature superconducting (HTS) conductor with a large current capacity applicable to a nuclear fusion experimental device, REBCO (REBa <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> CuO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">y</sub> ) tapes and high-purity aluminum sheets are alternately laminated, placed in a groove of an aluminum alloy jacket having a circular cross section, and the lid is friction-stir welded. To make the current distribution and mechanical characteristics uniform, the conductor is twisted at the end of the manufacturing process. In the early prototype conductor, when the I <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">c</sub> was measured in liquid nitrogen under self-magnetic field conditions, I <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">c</sub> degradations were observed from the beginning, and the characteristic difference between the two prototype samples under the same manufacturing conditions were large. Furthermore, I <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">c</sub> degradation was progressed by repeating the thermal cycle from room temperature to liquid nitrogen temperature. This I <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">c</sub> degradation did not occur uniformly in the longitudinal direction of the conductor but was caused by local I <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">c</sub> degradation occurring at multiple locations. If the conductor was not manufactured uniformly in the longitudinal direction, the difference in thermal shrinkage between the REBCO tape and the aluminum alloy jacket caused local stress concentration in the REBCO tape and buckling occurred. Element experiments to explain this mechanism were conducted to clarify the conditions under which I <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">c</sub> degradation due to buckling occurs. Then prototype conductors were tested with improved manufacturing methods, and as a result, I <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">c</sub> degradation could be suppressed to 20% or less. We have achieved the prospect of producing a conductor with uniform characteristics in the longitudinal direction.

Rotating magnetization method for inspection of local defect in HTS conductor

High temperature superconducting (HTS) magnet used for a accelerator for high energy physics or a large-scale magnetic confinement system for nuclear fusion requires large current capacity HTS conductor in order to dump the stored magnetic energy quickly to protect the coil when quench has been occurred. To realize the HTS conductor, superimposed or stacked HTS tapes conductors are invented. However, local degradation of the critical current has been observed in the production of HTS conductors. Therefore, to confirm the soundness of the HTS conductor, it is necessary to establish the non-destructive detection method for the observation of degraded HTS tapes. In this study, we have investigated to inspect the degradation position in stacked HTS tapes by adopting rotating magnetization measurement method. This measurement method is measuring magnetization signal by rotating and transporting stacked HTS tapes in a static magnetic field. As a result, intentionally introduced buckling defect positions were detected by this measurement method.

Magnetization Loss of CORC With Various Configurations of 2G HTS Strands

The high temperature superconducting (HTS) conductors for electrical power devices and machines should have large current capacity and low AC loss. Conductors on round core (CORC) is one of the promising conductors that have the characteristics. It consists of helically wound HTS tapes on the round core of copper. We simulated a striated HTS tape of CORC with multiple conductors in parallel. Two HTS tapes with the width of 6 mm emulated a 12 mm tape with one striation and three HTS tapes with the width of 4 mm emulated the one with two striations, and so on. The performance of CORC depends on the diameter of the core former and the pitch of the helical winding. First, we investigated the characteristics of the critical current by the diameters of the core formers and the pitch lengths for 6 mm HTS tapes. And then we measured the magnetization losses of several samples for the emulation of the striation. We also measured the losses of the samples with the 24 mm wide strands. All samples have been made twice for 2 different types. One set had no end-connections. So, the parallel HTS tapes did not connect with each other. The other set had joints at both ends. So, there can be the circulating currents between the parallel tapes. Finally, we rotated all samples during the measurement step by step. We confirmed that the angular position of CORC sample to the magnetic field did not affect the magnetization losses.