Current Wire Research Articles

A novel REBCO conductor design to reduce screening-current field in REBCO magnets

Due to its very high critical fields, the second-generation high-temperature superconductor (2 G HTS) has been, and is being, used in high-field magnets. However, a persistent screening current induced in the REBCO conductor under time-varying conditions distorts the magnetic field, spatially and temporally. We describe a novel REBCO conductor design composed of narrow-stacked (NS) wire, a bundle of 1 mm wide REBCO tapes. The design is based on a fundamental notion that the narrower the REBCO tape width, the smaller the screen-current field (SCF). In this paper, both experimental and simulation work were carried out to analyze SCF in a REBCO coil wound with an NS wire. We demonstrate that the critical current of NS wires can be consistent with the conventional REBCO tape to meet the application requirements. Meanwhile, NS wire indeed substantially results in small SCF, an important requirement in high-field magnets such as for NMR, MRI, and HEP that may rely on REBCO conductor.

Comparison of interfacial and critical current behaviour of Al+Al2O3 sheathed MgB2 wires with Ta and Ti diffusion barriers

We present a comparative study of the interfacial reactions for the MgB2 wires with different diffusion barriers (Ta or Ti) and the outer (Al + Al2O3) sheath with variable Al purity and Al2O3 content. The reaction of (Al + Al2O3) with Ta produces non-uniform but considerably thinner interfacial layer than with Ti. The critical currents (Ic) of the MgB2 wires with Ta barrier do not vary any significantly for different heat treatment conditions, and in contrast, those with Ti barrier show a strong variation with Al purity and volume % of Al2O3 particles in the (Al + Al2O3) sheath. For the (Al + Al2O3) sheathed wire with Ti barrier, the maximum Ic is attained when the highest purity of 99.995% Al is used although the thickest reaction zone has developed at the Ti–(Al + Al2O3) interface. The critical current values suggest that not the interfacial reaction kinetics of barrier–sheath rather the purity of the Al powder and the volume % of Al2O3 particles in sheath determine the current carrying ability of the MgB2 composite wires. The current-voltage characteristics of wires when combined with the reaction behaviour at barrier–sheath interfaces, the (Al + Al2O3) sheathed MgB2 wires with Ti diffusion barrier looks more promising than Ta for engineering applications.

Influence of Cabling on Current Characteristics of Round MgB2 Wires With Different Design

MgB 2 superconductors are currently considered as a prospective for different applications, in particular for use in high-current superconducting electrical power lines. The MgB 2 superconductors are rather sensitive to the strain that unavoidably occur during a cabling process, that is why a standard cabling machine should be adapted for minimization of strain before fabrication of cables based on MgB 2 wires. We performed the comparative study of critical current gradation of two round ex situ MgB 2 wires during the fabrication the model 18-strand cable. Both wires were produced by the Columbus superconductor and differ by mechanical properties, matrix composition, and initial critical current. Our cabling machine was previously modified for minimization of strain on the base of calculations of strains dependencies on bending and twisting of MgB 2 wires. Mechanical properties of MgB 2 wires were analyzed as well. The changes of critical currents of both wires during the 18-strand cable fabrication and insulation were measured. The results of calculations, critical currents tests, and mechanical properties are presented and discussed.

Measurements and Modeling of Mechanical Properties of Nb3Sn Strands, Cables, and Coils

High-field Nb3Sn magnets for the next generation of hadron colliders are known to have long trainings and to be limited at 90% of their short sample limit at best. This means that the conductor current is at 60% or less of its critical value. Homogeneous finite-element models are typically used for the complex system that includes coils, wedges, poles, yoke, rods, keys, shoes, fillers, shell, etc. Through both modeling and measurements of mechanical properties, we show how a more accurate sub-modeling of the composite structure allows for a better understanding of the stress and strain distributions. This is extremely important for Nb3Sn performance since state-of-the-art high critical current wires of this superconductor are particularly sensitive to strain.

Design optimization and evaluation of the 3 kA MgB2 cable at 4.3 K for the superconducting link project at CERN

High-current superconducting links (SC links) are being developed at CERN for powering the superconducting magnets of the High-Luminosity Large Hadron Collider upgrade. The links contain MgB2 cables, each about 100 m long, rated at currents of up to 18 kA. The assembly of the cables is carried out with reacted wires; cable geometry and cabling processes take into account the mechanical properties of the reacted MgB2 conductor. The production of the cables as well as their final installation requires good mechanical stability, flexibility and electrical performance. The superconductor should have good mechanical strength in view of the stresses during cabling (tension and bending), operation at cryogenic temperatures (Lorentz forces and thermal contraction) and handling installation (tension and bending) at room temperature. Moreover, the electrical integrity of the MgB2 wire (IC degradation ≤5%) should be ensured after the cabling process for the SC links. Therefore, the study of the mechanical properties of the MgB2 wire and the definition of the cable design parameters are crucial for the project. In the present work we report on the optimization and validation of the design of the 18-strand, 3 kA MgB2 cable by assessing the electromechanical behaviour of 3 kA MgB2 superconducting cables produced with different cabling parameters. The critical current (IC) of the MgB2 wires was measured after triple bending and axial tensile load, and strands extracted from the cables were tested to quantify the critical current degradation. Electrical measurements of two, 2 m long, 18-strand MgB2 cables were carried out in the FRESCA test facility at CERN and no degradation was observed. Cabling parameters such as the bending radius and the twist pitch were evaluated, and the most appropriate geometries for the MgB2 18-strand cables have been selected. Numerical simulations were performed to allow a detailed study of the strains developed in the MgB2 strands due to the mechanical loading. The present results have been successfully transferred to industry for the first industrial production in the framework of the SC Link project.

DESIGN OF A SINGLE-PHASE RADIAL FLUX PERMANENT MAGNET GENERATOR WITH VARIATION OF THE STATOR DIAMETER

This study aims to observe the influence of the changing stator dimension on the air gap magnetic flux density (Bg) in the design of a single-phase radial flux permanent magnet generator (RFPMG). The changes in stator dimension were carried out by using three different wire diameters as stator wire, namely, AWG 14 (d = 1.63 mm), AWG 15 (d = 1.45 mm) and AWG 16 (d = 1.29 mm). The dimension of the width of the stator teeth (Wts) was fixed such that a larger stator wire diameter will require a larger stator outside diameter (Dso). By fixing the dimensions of the rotor, permanent magnet, air gap (lg) and stator inner diameter, the magnitude of the magnetic flux density in the air gap (Bg) can be determined. This flux density was used to calculate the phase back electromotive force (Eph). The terminal phase voltage (V∅) was determined after calculating the stator wire impedance (Z) with a constant current of 3.63 A. The study method was conducted by determining the design parameters, calculating the design variables, designing the generator dimensions using AutoCad and determining the magnetic flux density using FEMM simulation. The results show that the magnetic flux density in the air gap and the phase back emf Eph slightly decrease with increasing stator dimension because of increasing reluctance. However, the voltage drop is more dominant when the stator coil wire diameter is smaller. Thus, a larger diameter of the stator wire would allow terminal phase voltage (V∅) to become slightly larger. With a stator wire diameter of 1.29, 1.45 and 1.63 mm, the impedance values of the stator wire (Z) were 9.52746, 9.23581 and 9.06421 Ω and the terminal phase voltages (V∅) were 220.73, 221.57 and 222.80 V, respectively. Increasing the power capacity (S) in the RFPMG design by increasing the diameter (d) of the stator wire will cause a significant increase in the percentage of the stator maximum current carrying capacity wire but the decrease in stator wire impedance is not significant. Thus, it will reduce the phase terminal voltage (V∅) from its nominal value.

Nonequilibrium skyrmion accumulation induced by direct current in Ir/Co/Pt heterostructure

We investigated the current-induced dynamics of magnetic skyrmions in Pt/Co/Ir trilayers thin films. Skyrmions segregate in the transverse direction to the current flow via the skyrmion Hall effect, which shows scalability for current density and wire width. We also found the non-local accumulation of nonequilibrium skyrmions under charge current, which has an analogy with the spin accumulation in the nonlocal configuration.

Determination of long-term permissible currents in wires of power supply systems of railways

In the standard for contact wires made from copper and its alloys, the values of long-term permissible temperatures have significantly decreased. This requires recalculation of previously valid values of long-term permissible currents. Authors considered revised method for calculating the long-term permissible currents, based on a more rigorous consideration of the laws of heat transfer and experimental studies of the conditions of heating and cooling of shaped (contact) and stranded wires. Technique is based on heat balance conditions, using which the sources of greatest inaccuracies become such quantities as cooled surface area, influence of wind direction, meteorological conditions, laws of change in heat transfer coefficient, effect on additional heating of solar radiation. Deviations when these indicators are taken into account by existing methods can cause errors of 40 % or more. Formulas for calculating the actual outer surface of stranded and shaped wires are given. The inadmissibility of calculating the surface area of the wires by their reference diameter is noted. Updated law of the change in heat transfer coefficient for stranded and shaped wires, as well as the degree of its dependence on wind speed and cooled surface, is given based on a summary of extensive domestic and foreign research. It is shown that with the longitudinal direction of the wind, the reduction of this coefficient occurs to a lesser extent than has been assumed so far. Authors propose method for taking into account an increase in the heat transfer coefficient under meteorological conditions characteristic of ice formation. The heat transfer coefficient of shaped and stranded wires in no case can not be taken as for round pipes with smooth surface. Existing method of accounting for solar radiation, which influences the additional heating of wires, leads to an unjustified and repeated exaggeration of this effect, since previously only the radiation incident on the wire was taken into account in the calculations. According to the laws of heat transfer, the temperature of the irradiated body does not depend on the incident, but on the resulting radiation, defined as the difference between the radiations incident on the body and emitted by it in accordance with its temperature. A formula for accounting for such heat transfer is proposed. The above methodology and calculation formulas allow performing reasonable calculations to determine the long-term permissible currents of individual stranded and shaped wires, as well as the contact network as a whole.

Natural Frequencies of Long Symmetric Multiconductor Transmission Lines

The goal of this paper is to approximate the natural frequencies of symmetric multiconductor transmission lines (MTLs). The MTLs consist of multiple parallel thin wires above the ground with a long horizontal section in the middle. The wire trajectories at the terminals can be arbitrary as long as the wires are identical. Then, the vector containing the wire currents can be expressed as a function of the current reflection coefficient matrices from the two ports. The reflection coefficient matrices are analytically approximated with an iterative approach. The iterative approach includes high-frequency phenomena and respects the nonuniformity of the wires. These effects are not considered with the classical transmission line theory. In the end, the natural frequencies of the coupled wires are approximated via fixed-point iteration. Frequency splitting, which is common for coupled resonant systems, is observed. This phenomenon is explained using common and differential modes. All analytic results are compared to a numerical reference. Very good agreement is observed.

Neuro-fuzzy modeling and solution of magnetic field inverse problem

The present paper intended to identify the locations of piecewise linearly connected shape of a carrying current wire and its current magnitude based on data of three-axis magnetic sensor array mounted either on a surface or inside a volume. At first, we tested a few classical numerical computation methods and the least square method. The results indicated that these methods were incommensurate for this application. Then, we applied a locally linear neuro-fuzzy (LLNF) model with tree learning for modelling and identification of a linear piece of current. Based on sensor array locations; we proposed nine scenarios, a few of which include superficial array, volumetric array and a mix of superficial and volumetric arrays. For each sensor array model, a neuro-fuzzy structure identification based on the mean square criterion was carried out to select the best number of locally linear models. We found that LLNF model with volumetric and mix sensor array identified the position coordination and magnitude of a linearly shaped current very well. Finally, we applied one of the best arrays and locally linear modelling to solve this magnetic field inverse problem for piecewise linearly connected shapes of current. Our method for solving this inverse problem proved successful.

Multifarious Transit Gates for Programmable Delivery of Bio-functionalized Matters.

Programmable delivery of biological matter is indispensable for the massive arrays of individual objects in biochemical and biomedical applications. Although a digital manipulation of single cells has been implemented by the integrated circuits of micromagnetophoretic patterns with current wires, the complex fabrication process and multiple current operation steps restrict its practical application for biomolecule arrays. Here, a convenient approach using multifarious transit gates is proposed, for digital manipulation of biofunctionalized microrobotic particles that can pass through the local energy barriers by a time-dependent pulsed magnetic field instead of multiple current wires. The multifarious transit gates including return, delay, and resistance linear gates, as well as dividing, reversed, and rectifying T-junction gates, are investigated theoretically and experimentally for the programmable manipulation of microrobotic particles. The results demonstrate that, a suitable angle of the gating field at a suitable time zone is crucial to implement digital operations at integrated multifarious transit gates along bifurcation paths to trap microrobotic particles in specific apartments, paving the way for flexible on-chip arrays of biomolecules and cells.

Longitudinal Propagation Characteristic of Pantograph Arcing Electromagnetic Emission With High-Speed Train Passing the Articulated Neutral Section

Based on the analysis of the practical measurement data of H-field values at three different sites along the longitudinal direction of the railway, this paper proposes an aerial catenary nonuniform transmission line model to predict longitudinal propagation characteristic of pantograph arcing electromagnetic (EM). According to the theory of EM field, EM emission field value measured at articulated neutral section (ANS) site is converted into the initial current of the contact wire. With the initial current, the current distribution on the contact wire and the EM field distribution along the railway when pantograph slid the ANS could be obtained by the proposed model. The validity of the proposed model is verified by the consistency of the theoretical results and the practical measurement at 0.5 MHz, which is the frequency point of the nondirectional radio beacon (NDB).

A numerical investigation of magnetic field effect on blood flow as biomagnetic fluid in a bend vessel

Abstract Targeted delivery of therapeutic agents such as stem cells and drugs using magnetic nanoparticles with the aid of an external magnetic field is an emerging treatment modality for many diseases. To this end, understanding the effect of magnetic field on hemodynamics in human body is of great importance. In this article, the effect of external magnetic field, induced by a straight current wire, on hemodynamics of blood flow in a 90° horizontal bend vessel with circular cross section was investigated numerically using ANSYS Fluent®. The blood was considered as laminar, Newtonian, steady and incompressible. To investigate the effect of non-uniform magnetic field effects on the blood flow, the ferrohydrodynamics principles (FHD) were employed. A user-defined function (UDF) was developed to apply the magnetic field effects as source terms. The magnetic susceptibility of blood in oxygenated (in arteries) and deoxygenated (in veins) blood vessels were considered negative and positive values, respectively. The effect of magnetic number, Reynolds number, curvature coefficient and the position of the current wire on flow velocity, static pressure, and shear stress were investigated. The results showed that the Wall Shear Stress (WSS) and static pressure were enhanced with the increase of magnitude of magnetic number. In addition, it was observed that magnetic field has superior impact on the hemodynamic of venous vessel (deoxygenated blood) in comparison with the hemodynamic of artery vessel (oxygenated blood). By studying the effect of curvature coefficient and Reynolds number on WSS, it is concluded that in high curvature coefficient and low Reynolds number, the effect of magnetic field is greater than low curvature coefficient and high Reynolds number, respectively.

Effects of Mechanical Force on Critical Current of Soldered-Stacked-Square (3S) HTS Wires

Narrowing high-temperature superconducting (HTS) tapes can effectively enhance the ability of antielectromagnetic interference. In addition, different structures of HTS wires are necessary for HTS applications. Thereby, a kind of soldered-stacked-square (3S) HTS Wires has been proposed. This paper presents a process of fabricating several 3S HTS wires. A normal second-generation (2G) HTS tape having 4-mm width was narrowed into four 1-mm-width narrow HTS tapes. The main propose of this paper is to study different effects of mechanical force on the critical current of 3S HTS wires. Therefore, we measured the critical current variation of these wires from the torsion, bending, and tension effects points of view, respectively. Compared with their initial critical current values, if the reduction of the influenced critical current is smaller than 5%, it can be considered that these 3S HTS wires are workable. Based on the results of the experiment, the limitations of mechanical force for these wire applications are: minimal twisting pitch of 64 mm, minimal bending diameter of 54 mm, and maximum tensile force of 374 N.

A New Method to Calculate Induced Current of Thin Wire over Anisotropic Ground under HPM

The time response analysis of wire structures is often carried out in free space or isotropic half-space, but the real ground is usually layered and has anisotropic properties. In this paper, the induced current of a thin wire over layered anisotropic half-space under a high-power microwave (HPM) is calculated by using the time-domain integral equation (TDIE) method. The reflection coefficient of a layered anisotropic medium is obtained by the general transmitting matrix (GTM) method combined with Fourier transform. The variation of the induced current on the thin wire under different incident conditions is analyzed.

Effect of neutron irradiation on Nb3Sn wire

A Nb3Sn wire which was manufactured for the ITER toroidal field coil conductor by a bronze route process was prepared for this study to investigate the effect of neutron irradiation on the critical current in a high magnetic field. The critical current of the virgin wire was measured in liquid helium with a 28 T hybrid superconducting magnet at the High Field Laboratory for Superconducting Materials in Tohoku University. It was also measured in vacuum with a heat conduction type variable temperature insert (VTI) at the International Research Center for Nuclear Materials Science at Tohoku University. The wire was irradiated at below 100 °C by fission neutrons at up to 4.9 × 1022 neutrons m−2 (>0.1 MeV) at BR2 in Belgium, and the critical current after the irradiation was evaluated with a VTI in the range of 8–15.5 T. The difference of the critical current measured with two facilities was discussed, focussing on Joule heating of the sample holder which was made of pure copper, and the neutron irradiation effect on the critical current was investigated in the range of up to 15.5 T. The results show that the critical current measured in vacuum becomes lower than that in liquid helium because of the temperature rise of the sample holder where the sample was soldered, the critical current was increased by the neutron irradiation, and the current ratio (IC/IC0) was almost constant of 1.75 in the range of 8–15.5 T at around 4 K.

Helical orbitals and circular currents in linear carbon wires.

Disubstituted odd-carbon cumulenes are linear carbon wires with near-degenerate helical π-orbitals. Such cumulenes are chiral molecules but their electronic structure consists of helical orbitals of both chiralities. For these helical molecular orbitals to give rise to experimentally observable effects, the near-degenerate orbitals of opposite helicities must be split. Here we show how pyramidalized single-faced π-donors, such as the amine substituent, provide a strategy for splitting the helical molecular orbitals. The chirality induced by the amine substituents allow for systematic control of the helicity of the frontier orbitals. We examine how the helical orbitals in odd-carbon cumulenes control the coherent electron transport properties, and we explicitly predict two modes in the experimental single-molecule conductance for these molecules. We also show that the current density through these linear wires exhibits strong circular currents. The direction of the circular currents is systematically controlled by the helicity of the frontier molecular orbitals, and is therefore altered by changing between the conformations of the molecule. Furthermore, the circular currents are subject to a full ring-reversal around antiresonances in the Landauer transmission, emphasizing the relation to destructive quantum interference. With circular currents present around truly linear carbon wires, cumulenes are promising candidates for novel applications in molecular electronics.

Targeting a channel coating by using magnetic field and magnetic nanofluids

In this paper, the magnetic nanofluids and magnetic field are used to provide a coating around the wall of a channel. The magnetic field is induced by the direct current wire. Iron oxide is used as magnetic nanoparticles. A finite volume method is used to solve the Navier–Stokes equations, and the Eulerian–Lagrangian approach is employed to track the magnetic nanoparticles. The effects of magnetic strength, the position of current wire, and the diameter of magnetic nanoparticles on the trajectory of magnetic nanoparticles and coating efficiency are investigated by providing contours and diagrams. The results show that the length of coating decreases by about 55% with the increase in the particle diameter in the range of 500 nm to 1 μm. Further, the coating efficiency, defined as the ratio of the number of trapped particles on the wall to the number of injected particles at the inlet of the channel, improves by increasing the magnetic strength and decreasing the vertical position of the current wire.

Spin and motion dynamics with zigzag ion crystals in transverse magnetic gradients

We investigate the dynamics of ion crystals in zigzag configuration in transverse magnetic field gradients. A surface-electrode Paul trap is employed to trap 40Ca+ ions and features submerged current wires to generate magnetic field gradients of up to 16.3(9) T m−1 at the ions position. With the gradient aligned in the direction perpendicular to the axis of weakest confinement, along which linear ion crystals are formed, we demonstrate magnetic field gradient induced coupling between the spin and ion motion. We perform sideband spectroscopy upon directly driving the spins with a radiofrequency field for crystals of three ions on their linear-to-zigzag structural transition. Furthermore, we observe the rich excitation spectrum of vibrational modes in a planar crystal comprised of four ions.

A MATHEMATICAL MODELING OF AC ELECTRIC LOCOMOTIVE WITH ACTIVE CONVERTER IN TRACTION

One of the ways to increase the power factor of AC electric locomotives with DC traction motors is the use of converters on fully controlled semiconductor devices — active current source rectifiers. However, the modes of operation of the active current source rectifier as a DC voltage regulator have not been studied enough today and require further investigation. In this article, a mathematical model of an AC electric locomotive with an active traction converter (based on the eight-axle freight AC locomotive 2EL5) with two-zone regulation of the DC voltage is developed. The model of the “traction network — electric locomotive” system is presented in the form of differential equations. The algorithm of the active converter control system is described by logical switching functions. The converter uses a unipolar rectangular-stepped pulse width modulation with a carrier frequency of 1200 Hz. Computer modeling of electromagnetic processes in the traction mode is performed. The oscillograms of voltages and currents show the process of transition from the first control zone to the second one. According to experiments, the power factor of an electric locomotive in the entire control range is 0.83...0.99. This is more than a thyristor converter. The THDi of the trolley wire current is about 9...10%. Analysis of the trolley wire voltage and current waveforms showed that a decrease in the modulation index has a negative effect on the voltage and current harmonic distortion. Further research should focus on limiting the higher harmonics of voltage and current when adjusting the voltage. The practical result of the use of active traction converters on electric locomotives is a reduction in the consumption of electric power for the traction of trains.