Superconducting Elements Research Articles

Literature Review of Suspension Systems for Superconducting Elements

When designing suspension systems for superconducting elements, the primary challenge is to strike a balance between limiting the heat load to the cold mass and ensuring the proper mechanical resistance and/or stiffness of the system. This trade-off often leads engineers to choose from a limited set of materials and supporting architectures. The aim of this study is to provide an overview of the different overall designs. Scientific articles were searched within the Google Scholar database using advanced search operators to combine a defined set of keywords. Among the architectures found, the “multi-post” solution and the “8-support” solution are the two most commonly chosen classes. Additionally, a recurrent pattern for the supporting system of superconducting cavities has been identified. The choice of architecture can be correlated with the characteristics of the superconducting element being supported, such as its mass, length, and stiffness. Furthermore, the review provides a conceptual analysis of the possibility of extending these designs to the unconventional environment of rotating machines.

A Study on Increasing the Capacity of Transformer-Type Superconducting DC Circuit Breaker

Superconducting Fault Current Limiter (SFCL) can increasethefaultcurrent-limitingratethroughtheseriesconnection of superconducting elements, and through this, it can be applied to systems with high capacity. However, when multiple superconduct-ing elements are connected in series, unbalanced quench character-istics may occur continuously due to problems of critical character-istics andpartialquenching.Wehaveproposedaquenching method ofbalancedSFCLusingthe neutrallinetosolvethisproblem.Inthis paper, we applied several superconducting elements with the neu-trallinetoincreasethecurrent-limitingrateofthetransformer-type superconducting current limiter module (T-SFCL module). Inaddi-tion, when the T-SFCL module was combined with the DC circuit breaker, the operating characteristics of the superconducting DC circuit breaker were confirmed. As a result, power consumption of superconducting elements was balanced due tothe balanced quench of superconducting element, and fault current was reduced due to the highcurrentlimitingcharacteristics of superconducting element.

Quantum Hall valley ferromagnets as a platform for topologically protected quantum memory

Materials hosting topologically protected non-Abelian zero modes offer the exciting possibility of storing and manipulating quantum information in a manner that is protected from decoherence at the hardware level. In this paper, we study the possibility of realizing such excitations along line defects in certain fractional quantum Hall states in multivalley systems. Such line defects have been recently observed experimentally between valley polarized Hall states on the surface of Bi(111), and excitations near these defects appear to be gapped (gapless) depending on the presence (absence) of interaction-induced gapping perturbations constrained by momentum selection rules, while the position of defects is determined by strain. In this paper, we use these selection rules to show that a hybrid structure involving a superlattice imposed on such a multivalley quantum Hall surface realizes non-Abelian anyons, which can then be braided by modulating strain locally to move line defects. Specifically, we explore such defects in Abelian fractional quantum Hall states of the form $\ensuremath{\nu}=2/m$ using a K-matrix approach, and identify relevant gapping perturbations. Charged modes on these line defects remain gapped, while charge neutral valley pseudospin modes may be gapped with the aid of two (mutually orthogonal) superlattices, which pin noncommuting fields. When these superlattices are alternated along the line defect, non-Abelian zero modes result at points where the gapping perturbation changes. Given that these pseudospin modes carry no net physical charge or spin, the setup eschews utilizing superconducting and magnetic elements to engineer gapping perturbations. We provide a scheme to braid these modes using strain modulation, and confirm that the resulting unitaries satisfy a representation of the braid group.

Influence of cooling conditions of HTS assembly on the characteristics of a moving maglev system

Background: analysis of the influence of cooling conditions of high-temperature superconducting elements on the power characteristics of a maglev system under conditions of rapidly changing magnetic fields
 Aim: analysis of the influence of cooling conditions of high-temperature superconducting elements on the force characteristics of a magnetic-levitation transport platform under conditions of rapidly changing magnetic fields caused by the inhomogeneity of the magnetic track.
 Methods: numerical analysis of the maglev system was performed by the finite element method in the Comsol Multiphysics engineering simulation software.
 Results: at fast, more than 5 T/s, magnetic field change rates, due to the motion of the superconductor in a magnetic field with a non-uniform local distribution, the preferred method of cooling is the use of cryocooler technology. At rates of change of the magnetic field less than 5 T/s, it is permissible to use liquid nitrogen as a cooler.
 Conclusion: The developed numerical model makes it possible to predict the dynamic characteristics of levitation systems of various scales and can be applied to contactless transport, as well as in rotating machines, including kinetic energy storage devices.

Spin cross-correlation experiments in an electron entangler.

Correlations are fundamental in describing many-body systems. However, in experiments, correlations are notoriously difficult to assess on a microscopic scale, especially for electron spins. Even though it is firmly established theoretically that the electrons in a Cooper pair1 of a superconductor form maximally spin-entangled singlet states with opposite spin projections2-4, no spin correlation experiments have been demonstrated so far. Here we report the direct measurement of the spin cross-correlations between the currents of a Cooper pair splitter5-13, an electronic device that emits electrons originating from Cooper pairs. We use ferromagnetic split-gates14,15, compatible with nearby superconducting structures, to individually spin polarize the transmissions of the quantum dots in the two electronic paths, which act as tunable spin filters. The signals are detected in standard transport and in highly sensitive transconductance experiments. We find that the spin cross-correlation is negative, consistent with spin singlet emission, and deviates from the ideal value mostly due to the overlap of the Zeeman split quantum dot states. Our results demonstrate a new route to perform spin correlation experiments in nano-electronic devices, especially suitable for those relying on magnetic field sensitive superconducting elements, like triplet or topologically non-trivial superconductors16-18, or to perform Bell tests with massive particles19,20.

Utilizing Parallel Superconducting Element as a Novel Approach of Flux-Coupled Type SFCL to Limit DC Current in the System

To lessen the amount of energy lost during transmission, electricity is increasingly being sent using high-voltage lines. Transmission loss in a DC system is lower than in an AC system over long distances. The DC system can improve the efficiency of long-distance transmission by connecting power grids with different requirements. The DC method is becoming popular since it helps to keep the grid stable. Managing and blocking DC flow is crucial to system functionality. In this study, we explore the operation of a flux-coupled type superconducting fault current limiter (SFCL) in a DC system, where the two windings are connected in parallel to limit the fault current flow. A flux-coupled type SFCL is built by connecting two coils in parallel and a superconducting element (SE) in series with the secondary coil. The functions of an SFCL of the flux-coupled kind are equivalent in both direct and alternating current systems. Because of the opposing magnetic fluxes produced by the two coils, the voltage generated by the parallel connection of the coils is always zero. Inadequate SE leads to an increase in resistance, inhibiting the cancellation of opposing magnetic fluxes and hence a loss in power. Connecting the two coils in series allows voltage to be generated while the fault current is limited. To further validate the performance of SFCL with varying resistance and inductance, the system is additionally tested on the IEEE 39 bus system. The MATLAB/SIMULINK software suite is used to run the test system.

Comparison and Analysis of Impedance According to the Winding Method of Superconducting Element Connected to DC Circuit Breaker

DC Interruption technology is essentially required as DC systems and microgrids have increased. The Interruption technology also includes current limiting technology. Until now, many hybrid Interruption technologies have been proposed in which a semiconductor element or a superconducting element is combined with a mechanical DC circuit breaker. In this paper, an interrupting test was performed by combining a superconductor and a DC circuit breaker. The advantage of circuit breakers combined with superconducting elements is that they do not cause losses and effectively limit the fault current. When the fault occurs, if the fault current exceeds the critical value of the superconducting material, resistance occurs in the superconducting element. The fault current is limited by the resistance generated during quenching and resonates due to the LC divergence oscillation circuit. The current flowing through the mechanical circuit breaker reaches zero-point by resonance. After that, the mechanical breaker is completely opened, and the fault current is interrupted. Superconducting elements exhibit different characteristics depending on their winding method, material, and length. The purpose of this study is to comparatively analyze solenoid and toroid coil type superconducting elements. Both types are made with the same number of turns, permeability, and length. As a result of the experiment, the toroid coil has generated more impedance than the solenoid coil.

DTT: A Challenging Framework for a Sound Superconducting Magnets Design

At the ENEA's research center of Frascati, the DTT (Divertor Tokamak Test) facility is currently under construction. The activity of this experimental nuclear fusion reactor, will be focused on the optimization of the power exhaust management in view of DEMO. The project has been started during year 2015, when also the superconducting magnet system has been initially designed, basing on the available inputs coming from physics and on the desired goals for the machine. At present, the coils engineering design has almost been completed and the production of crucial components, such as the superconducting strands, conductors and toroidal field coils, have already been started. For the remaining superconducting elements, the engineering design is being finalized and other tenders are going to be launched soon. The result is a compact and flexible tokamak, with highly demanding requirements in terms of superconducting and structural performances, sometime close to the intrinsic mechanical limits of the adopted materials. Tight constraints on time, budget and resources forced the design team to walk through a complex path in these years for reaching a sound and satisfactory design of the complete magnet system. In fact, it was not possible to rely entirely on state-of-the-art and already assessed superconducting technologies, as was initially assumed. In particular, the trade-off between limiting the R&D phase and extending the performance demonstrated in other projects to the specific DTT requirements, pushed the team to take some risks, while providing a robust and fully performing magnet system design.

Mesoscopic superconducting memory based on bistable magnetic textures

With the ever-increasing energy need to process big data, the realization of low-power computing technologies, such as superconducting logic and memories, has become a pressing issue. Developing fast and non-volatile superconducting memory elements, however, remains a challenge. Superconductor-ferromagnet hybrid devices offer a promising solution, as they combine ultra-fast manipulation of spins with dissipationless readout. Here, we present a new type of non-volatile Josephson junction memory that utilizes the bistable magnetic texture of a single mesoscopic ferromagnet. We use micromagnetic simulations to design an ellipse-shaped planar junction structured from a Nb/Co bilayer. The ellipse can be prepared as uniformly magnetized or as a pair of vortices at zero applied field. The two states yield considerably different critical currents, enabling reliable electrical readout of the element. We describe the mechanism used to control the critical current by applying numerical calculations to quantify the local stray field from the ferromagnet, which shifts the superconducting interference pattern. By combining micromagnetic modeling with bistable spin-textured junctions, our approach presents a novel route towards realizing superconducting memory applications.

Magnetic Memory Effect in Planar Ferromagnet/Superconductor/Ferromagnet Microbridges Based on Highly Diluted PdFe Alloy

The magnetoresistance of a planar microbridge based on a three layer Pd0.99Fe0.01–Nb–Pd0.99Fe0.01 FSF sandwich near its superconducting transition is studied. We previously showed that the magnetoresistance curve of such samples is hysteretic and contains dips (negative peaks of the resistance) in the coercive fields. In this work, it is found that the low-resistance state has a memory effect. Functioning of such a sample as a superconducting memory element is demonstrated. The effect of the ferromagnetic Pd0.99Fe0.01 layer on the superconducting transition temperature of the proposed memory element is studied by measuring the dep-endence of the critical temperature of bilayer Pd0.99Fe0.01–Nb FS structures on the thickness of the Pd0.99Fe0.01 layer.

Experimental study of elements of a Josephson traveling-wave parametric amplifier on SQUID chains.

The issues of designing a Josephson traveling-wave parametric amplifier (JTWPA) based on a well-established technology of superconducting microcircuits with given and controlled parameters based on high-quality Nb-AlOx-Nb tunnel junctions are considered. This technology has been adapted and optimized to obtain structures with the required parameters and circuits with large number of tunnel junctions. To advance the technology, the basic elements of a promising JTWPA have been devel-oped, manufactured and studied. In direct current measurements, a number of super-conducting elements parameters were experimentally determined; these parameters are required for designing a JTWPA chips for microwave measurements. An original design of JTWPA based on a chain of SQUIDs in a coplanar line has been developed for implementation using the IRE niobium technology; the parameters of the main elements of the JTWPA have been determined. Keywords: Josephson travelling-wave parametric amplifiers (JTWPA), Josephson metamaterials (JMM), Josephson junctions (JJs), cold amplifier, coplanar lines, quantum noise, SIS, SQUIDs.

Analysis of Debye Temperature and Transition Temperature of Cubic Structured Superconducting Elements

Analysis of Debye Temperature and Transition Temperature of Cubic Structured Superconducting Elements

Экспериментальное исследование элементов джозефсоновского параметрического усилителя бегущей волны на цепочке СКВИДов

The issues of designing a Josephson traveling-wave parametric amplifier (JTWPA) based on a well-established technology of superconducting microcircuits with given and controlled parameters based on high-quality Nb-AlOx-Nb tunnel junctions are considered. This technology has been adapted and optimized to obtain structures with the required parameters and circuits with large number of tunnel junctions. To advance the technology, the basic elements of a promising JTWPA have been devel-oped, manufactured and studied. In direct current measurements, a number of super-conducting elements parameters were experimentally determined; these parameters are required for designing a JTWPA chips for microwave measurements. An original design of JTWPA based on a chain of SQUIDs in a coplanar line has been developed for implementation using the IRE niobium technology; the parameters of the main elements of the JTWPA have been determined.

Analysis of Debye Temperature and Transition Temperature of Cubic Structured Superconducting Elements

Analysis of Debye Temperature and Transition Temperature of Cubic Structured Superconducting Elements

Power consumption and cumulative energy of bridge type SFCL with simultaneous quench

A bridge type superconducting fault current limiter (SFCL) with two high-temperature superconducting (HTSC) elements using flux-coupling is proposed to reduce the influence of short-circuit accidents. A laboratory-scale prototype SFCL was fabricated and short-circuit test was conducted. The power consumption and the accumulated energy were compared and analyzed according to the winding current when the number between N1 and N2 coil changed during the fault period. In addition, the operating range of the flux linkage and the variation of the magnetizing force area were compared according to the magnetizing current. The usefulness of the proposed SFCL was confirmed through analysis of the fault current limiting operation characteristics and the energy consumed by the simultaneous quench of two HTSC elements. As a future study, we will apply this modified bridge-type SFCL model to a direct current (DC) distribution system. First, after establishing a DC short circuit accident test environment, this SFCL is constructed in front of the DC load and the fault occurrence resistor to measure and analyze the DC fault current limiting characteristics.

Твердотельные магнитные материалы для магнито-левитационного транспорта.

Study and implementation of innovative systems of environmentally friendly and energy-efficient transport based on magnetic levitation, the principle of operation of which is based on the use of new solid-state magnetic materials based on compounds of rare earth materials, in particular materials with high-temperature superconductivity based on Y, permanent magnets based on Nd and Sm and magnetocaloric alloys based on Dy, Tb are of great interest throughout the world. In this work, the basic principles of magneto-levitation transport with the most economical principle of acceleration and deceleration - gravitational - are studied experimentally on mock-ups. The strength characteristics were measured: the levitation force and the lateral stabilization force, as well as losses during periodic translational motion of a cryostat with high-temperature superconducting elements made of ceramic material Y-Ba-Cu-O over the paths of permanent magnets made of the rare-earth compound Nd-Fe-B. A system for measuring the speed and compensation of losses for the implementation of continuous motion has been created and tested. The presented results indicate the possibility of scaling the layout project. It is concluded that the investigated scheme may be of practical interest for intracity and local transport communication with high comfort, environmental friendliness and record economy in the case of a successful solution of the problem of cooling HTSC elements to the temperature of the phase transition to the superconducting state, for example, using new principles of solid-state magnetic cooling based on compounds Dy-N, Tb-Ni, etc.

PSCAD/EMTDC를 활용한 초전도 소자의 유무에 따른 기계식 DC 차단기 분석

With the announcement of a policy to reduce carbon emissions, the range and technologies of renewable energy sources are increasing. In new renewable energy, the amount and range of solar power generation is relatively gradually expanding[1]. Based on the high-speed DC circuit breaker used in the solar power generation, we combined the LC divergence oscillation circuit and the superconducting element that this research team is working on. This is to protect peripheral equipment against an increase in solar power generation and unspecified disturbances. The DC circuit breaker, we propose is a mechanical DC circuit breaker with a superconducting element applied. The superconducting element can lower the initial fault current within about 2 ㎳ through the quenching operation. However, it takes a large power burden and a long time to cut-off the fault current. In the mechanical DC cut-off part, the existing high-speed mechanical circuit breaker, LC divergent oscillation circuit and Surge Arrestor are connected in parallel to safely and reliably cut off fault current. The characteristics of the cut-off operation that appear when a superconducting element and an LC divergent oscillation circuit are combined with a conventional mechanical DC circuit breaker were analyzed. As a result, through the application of the superconducting element, the speed at which the artificial zero-point of the fault current occurs was reduced, and the time to complete the shutdown was shortened.

Novel Design of a Hybrid Superconducting Fault Current Limiter with Controlled Solid-State Device

Fault current limiters are essential devices used to protect the power system and its equipment against high levels of fault current, which are growing up due to the increase of new power sources. This paper proposes a novel design of a Hybrid Superconducting Fault Current Limiter (Hybrid SFCL), which is composed basically by thyristors in series with a superconducting element. This branch is connected in parallel to an air-core reactor, which improves limitation and ensures the safe operation of the superconductor element. Another advantage of this topology is the use of the voltage drop in the superconductor as an input parameter to the controller. This voltage is used to detect the fault, which avoids the need for a current sensor and, consequently, reduces the manufacturing costs. In this work, the PSCAD/EMTDC software was employed to modeling the Hybrid SFCL and the 2G superconducting tape, which was modeled considering the thermal-electrical analysis. The results show that the fault current is efficiently limited, and the developed controller strategy has shown a relatively good performance. Furthermore, the proposed system guarantees a fast recovery time, in the order of 500 ms, which is a good advantage when compared to the conventional resistive SFCL.

DC Current Limiting Characteristics of Flux-Coupled Type SFCL Using Superconducting Element Connected in Parallel in a DC System

In this paper, the fault current limiting (FCL) characteristics of a flux-coupled type superconducting fault current limiter (SFCL) with parallel connection between two windings in a DC system were analyzed. The flux-coupled type SFCL was composed of two coils connected in parallel and a superconducting element (SE), which was connected in series with the secondary coil. The flux-coupled type SFCL works in DC systems similar to those in AC systems. Before a fault occurs, the respective magnetic fluxes generated by the two coils connected in parallel offset each other, maintaining the voltage induced in the two coils at zero. In case of a fault, however, resistance is generated in the SE, preventing the magnetic fluxes generated by the two coils from offsetting each other. Thus, some voltage is induced in the two coils, and this starts to limit the fault current. DC short circuit tests were conducted, and the test results confirmed that the flux-coupled type SFCL with the two parallel connected coils was effective in limiting the fault current in a DC system. Additionally, the effect of the wiring direction of the two coils on the SFCL’s FCL performance and operating current, limiting impedance, and instantaneous power load was further analyzed, and as a result, the performance conditions of the SFCL in a DC system were determined.

Magnetization and Power Losses Characteristics Due to Variation in the Number of Windings of Bridge Type SFCL with Double HTSC Elements

Superconducting fault current limiters (SFCLs) are emerging as an alternative to limit fault current in AC and DC power systems. SFCLs can perform faster current limiting operation and automatic fault current detection and recovery, regardless of the type of fault. In this paper, a laboratory-scale prototype SFCL was fabricated and analyzed for its magnetization characteristics due to the magnetizing current according to the change of the number of windings in pairs. This bridge type SFCL consists of two windings and two high-Tc superconducting (HTSC) elements on one iron core. When the number of windings of the two coils were changed in pairs, the variation of the induced voltage and Joule losses due to the magnetizing current, magnetic flux in each winding, and power losses for the bridge type SFCL were compared with each other. Through comparative analysis, it was confirmed that the size of the number of turns should be considered to reduce the power losses of SFCL while effectively limiting the fault current during the fault cycle.