Coil Conductor Research Articles

Overhead conductor heating chamber and temperature effects on the fatigue life of aluminum alloy 6201‐T81 conductors

AbstractThis work investigates the impact of temperature on the fatigue life All Aluminum Alloy Conductors (AAAC) made of 6201‐T81. A heating chamber was developed to simulate thermal effects induced by electric current passage. Wöhler fatigue curves were generated under isothermal conditions at 75 and 150°C and later compared with the one at 20°C. The conductor exhibited similar fatigue life at 20 and 75°C; however, a significant increase of life was observed for tests at 150°C. Hardness tests and failure analysis of wire breakages were carried out on samples extracted from the conductor coil and on artificially aged samples maintained at controlled temperatures. The analyses revealed that at a temperature of 150°C, there is formation of small precipitates of magnesium and silicon within the aluminum matrix, which impeded the propagation of discontinuities, increasing the material's hardness and fatigue resistance.

Effects of Resonance Phenomenon on Voltage Between Conductors in JT-60SA PF Coils

Effects of Resonance Phenomenon on Voltage Between Conductors in JT-60SA PF Coils

Dual-Channel Transverse Fields Radiofrequency Coils for 1.5 T Magnetic Resonance Imaging.

This theoretical study presents the design and analytical/numerical optimization of novel dual-channel transverse fields radiofrequency (RF) surface coils for 1.5 T Magnetic Resonance Imaging (MRI). The research explores a planar setup with two channels on a row with aligned spatial orientation of the RF coils, aiming to solve a common design drawback of single-channel transverse field RF coils: the reduced Field Of View (FOV) along the direction of the RF field. A significant challenge in this design is the efficient decoupling of two sets of transverse field RF coils to prevent mutual interference. Our modeling approach integrates thin wire theoretical modeling, magnetostatic computation for strip conductor coils, and their full-wave electromagnetic simulation. Key findings at 64 MHz demonstrate that strategic geometric placement among the two-channel RF coil and the introduction of geometrical asymmetry in the design of the individual RF coils does minimize the mutual inductance, paving the way for effective dual-channel MRI applications. This decoupling approach allows to enhance the FOV, providing a theoretical framework for the development of optimized dual-channel transverse field RF coil configurations. The current design was validated with full-wave numerical study at 64 MHz (1H, 1.5 T), has the potential to be extended at lower or higher frequencies, and the presence of lossy samples needs to be considered in the latter case.

Commissioning and optimization of superconducting undulator in the horizontal state

Taking advantage of a higher field than a conventional permanent magnet undulator, superconducting undulators (SCUs) have been rapidly developed in recent years for applications at synchrotron radiation sources and free-electron lasers. The Institute of High Energy Physics, Chinese Academy of Sciences, has developed a 1.5-m long planar SCU with a short period of 15 mm. This SCU has been commissioned and optimized in the horizontal position. In contrast to the vertical position, where the undulator coils are immersed in liquid helium for superconductivity, the horizontal test requires the assembly of the complete device, including the cryostat, current conductor, cryocooler, vacuum chamber, and undulator coils. This test reflects the operation status and measures the SCU’s characteristics under working conditions. Although experiences from the vertical test provided good guidance for horizontal optimization, special care needs to be taken for effects such as gravity. After improving field uniformity through iterative measurements, the rms phase error of the SCU is reduced to 7.3° at a current of 400 A. Additionally, the functions of the end correction coils to mitigate field integral errors have been verified. This paper also demonstrates and analyzes other phenomena and interesting observations during the commissioning process. It discusses important issues that impact field quality and measurement accuracy and suggests further improvement measures for an even better field. Published by the American Physical Society 2024

Measurement and calculation of magnetic flux density generated by the second cooling zone electromagnetic stirring (S-EMS) of a slab continuous casting strand

In the current study, a measurement of the magnetic flux density in the second cooling zone was performed for a 1250 mm width and 200 mm thickness slab continuous casting strand generated by the electromagnetic stirring with varied current intensity and frequency. From the narrow face to the width center of the slab, the magnetic flux density showed a increased, decreased, increased to a peak, and finally decreased trend. The magnetic flux density was decreased from the wide side to the thickness center of the slab, while an increase occurred from the model top to the stirrer center along the casting direction. To broaden the measurement range of the electromagnetic stirring parameters, the electromagnetic field in the strand and stirrer was calculated based on the finite element method, and the current input was achieved using the node loading approach. The effect of the mesh density on the calculation accuracy was investigated, and it was found that the 20 mm cell size in the strand region and the 10 mm cell size in the coil conductor and the iron core were enough to achieve a good agreement between the calculation and measurement. The empirical equations, Bx = 0.165.f 0.63.I −0.57.(–6870.x4–9700.x3–4260.x2–495.x + 90), By = 0.167.f −0.5.I 0.45. (4272.y2 + 0.2733.y + 101.4), and Bz = 0.1724.f −0.5.I 0.45.(0.0191.exp(24.16.z − 16.12.z2) + 2.3) were derived to estimate the local magnetic flux density based on measured values across the width of the slab and calculated values along the casting direction under diverse operational conditions. These equations hold practical significance in elucidating the spatial distribution of magnetic flux density within the strand region in the second cooling zone.

HTS conductor coil by in-situ winding technology for large-scale high-field magnet

High temperature superconducting (HTS) conductors have become important candidates to be used in large-scale high-field magnets, owing to its high critical current density as well as good mechanical properties. At present, there are various forms of HTS conductors proposed. In this work, we reported the fabrication of the REBCO HTS coil using in-situ winding technology. The six-layer coil with a diameter of 410 mm achieved a total current of 2562 A, and generated a central magnetic field of 7.8 mT at 77 K. The stress, deformation, and defect caused during conventional winding procedure could be significantly decreased using in-situ winding technology, indicating it has great potential for the large-scale high-field magnets in next-generation fusion reactors.

Characterization of Electromechanical Delamination Behaviors in Practical REBCO Coated Conductor Tapes Under Transverse Tension at 77 K

In high-temperature superconducting coils, the high transport current density and magnetic field generate a large electromagnetic force on REBCO-coated conductor (CC) tapes. A large Lorentz force can cause interlayer delamination damage to the CC tape under radial or transverse tensile loads. The structural delamination characteristics of multilayered REBCO CC tape are essential for the fabrication of mechanically reliable CC coils. In this study, the electromechanical delamination behaviors of practical REBCO CC tapes were characterized using an anvil test method. Our recently established continuous critical current, I <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">c</sub> measurement system was used to minimize the test time and can directly evaluate the effect of the transverse tensile load on I <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">c</sub> behavior without time-consuming intermittent I <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">c</sub> measurements during testing. Characterization of the delamination mechanism, including damage initiation, was performed through scanning electron microscopy observation of the fractured sample. Two-parameter Weibull distribution analysis was used to specify the data scattering of the electromechanical delamination strength.

External Coil Coupled Loss Induced Quench (E-CLIQ) System for the Protection of LTS Magnets

The next generation of Nb <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$_{3}$</tex-math></inline-formula> Sn accelerator magnets are pushed to higher magnetic fields, higher stored energy and higher energy density. This brings additional challenges when it comes to quench protection. At CERN, a fast quench protection system is under development that introduces normal zones directly in the coil's conductor by inductive heating. This system is called External coil Coupled Loss Induced Quench (E-CLIQ). The E-CLIQ device comprises many small copper coils that are strategically placed near the main coils. Once a quench is detected, a capacitor is discharged in to the E-CLIQ coils, resulting in the characteristic damped oscillating current of an RLC circuit. This results in a large, but local applied dB/dt on the conductor of the main magnet system, which locally heats it by induced interfilament and interstrand coupling loss. Such a system has the advantage of being fast by introducing normal zones in potentially less than 10 ms, it doesn't rely on heat flow through the insulation layers of the coil, as is the case with traditional quench heaters, and it is not electrically connected to the main circuit. In this paper, the E-CLIQ system is introduced, several first demonstrator coils are presented and the results of a first proof-of-concept test are shown.

Current Distribution of Armature Coils Combining Two Different Sizes of REBCO Racetrack Double Pancakes

We are currently developing superconducting electric propulsion armature coils which utilize REBa2Cu3Oy (REBCO) strands. To implement the REBCO coils in aircraft, the voltage must be reduced for safety concerns by using high-current capacity. Parallel conductors can be used to expand the current capacity, but the current cannot flow equally through each strand owing to the slight difference in inductance. We have investigated transposed parallel conductors which can almost equalize the inductance of each conductor. Conversely, the distributed windings for the armature coils can improve the magnetic field waveform and transform it into a sine wave by reducing the distortion of the magnetic flux density about the rotating magnetic field. However, it is difficult to implement a distributed armature winding using the REBCO strands since it is tape-shaped and difficult to twist. Therefore, we propose a distributed armature winding which combines two types of racetrack double pancakes. Each double pancake comprises two-strand insulated REBCO superconducting parallel conductors transposed inside the pancake for current equalization. In this study, we perform an experimental demonstration of the current equalization based on the transposition of the distributed armature winding. We made coils with two-strand as a simplified, but the actual coils were needed more 10 strand parallel conductors. In future works, we will manufacture transposed parallel conductor coils using much more strands and measure the current distribution. Additionally, this study measured the current distribution with only the stater. Thus, we will combine the rotor and measure the magnetic field distribution of the rotating magnetic field in the armature.

The effect of coating concentration of curcumin: H2O on copper winding characteristics

Each coil of copper produces a magnetic field and the total field inside the solenoid will be the sum of the fields caused by each coil of current. If the solenoid coils are very closely spaced, the internal field will be essentially parallel to the axis except at the very ends. To find out the magnitude of the magnetic field inside the solenoid, you can use Ampere’s law, namely B=μo∙N∙I, where B is the magnetic field strength (T), µo is air permeability (4×10‒7 T m/A), N is the number of turns and I is an electric current. The value of B depends on the number of turns per unit length, N, and current I. The field is independent of the position inside the solenoid, so the value of B is uniform. This only applies to infinite solenoids, but is a good approximation for actual points that are not near the ends of the solenoid. The research object is 4 identical copper coils with a length of 3 cm, a coil diameter of 2 cm, a cross section of 1.5 mm2 with an inductance value of 2.17 µH. Before coating curcumin on the copper winding, the initial value of the magnetic field strength was 2.54 µTesla. After the coating process of curcumin:H2O concentration, the value of the magnetic field strength increased. The method used was immersing 4 copper coils with an inductance value of 2.17 µH in curcumin:H2O concentration in a 100 ml volume measuring cup, with the respective concentrations: (20 %:80 %), (40 %:60 %), (60 %:40 %), (80 %:20 %) in a certain time. Then the copper coil conductor is supplied with a 5-volt DC voltage source. Then the value of the magnetic field strength (B) and electric current is measured, the results are compared with the system before immersing the copper coil. The measurement results showed that the values of electric current and magnetic field strength increased after curcumin coating compared to before treatment. To see the bonding performance of curcumin and copper, the FTIR test and simulation of the curcumin: copper bond were carried out using Avogadro software. In the IR test, there is a strong absorption of aromatic C-C from 1,650 cm-1 to 1,500 cm-1. Whereas in the simulation, the bond between copper and curcumin produces a bond energy of 164.532 kJ/mol or equivalent to 171.12×10-2 eV

Conductor Losses in Radiofrequency Coils for Magnetic Resonance below 3T: Estimation Methods and Minimization Strategies

The design of optimized radiofrequency (RF) coils is a fundamental task for maximizing the signal-to-noise ratio (SNR) in Magnetic Resonance Imaging (MRI) and Magnetic Resonance Spectroscopy (MRS) applications. An efficient coil should be designed by minimizing the coil noise with respect to the sample noise, since coil conductor resistance affects data quality by reducing the SNR, especially for coils tuned to a low frequency. Such conductor losses strongly depend on the frequency (due to the skin effect) and on the conductor cross-sectional shape (strip or wire). This paper reviews the different methods for estimating conductor losses in RF coils for MRI/MRS applications, comprising analytical formulations, theoretical/experimental hybrid approaches and full-wave simulations. Moreover, the different strategies for minimizing such losses, including the use of Litz wire, cooled and superconducting coils, are described. Finally, recent emerging technologies in RF coil design are briefly reviewed.

Numerical simulations of an integrated radio-frequency/wireless coil design for simultaneous acquisition and wireless transfer of magnetic resonance imaging data

Objective. A novel magnetic resonance imaging (MRI) radio-frequency (RF) coil design, termed an integrated RF/wireless (iRFW) coil design, can simultaneously perform MRI signal reception and far-field wireless data transfer with the same coil conductors between the coil in the scanner bore and an access point (AP) on the scanner room wall. The objective of this work is to optimize the design inside the scanner bore to provide a link budget between the coil and the AP for the wireless transmission of MRI data. Approach. Electromagnetic simulations were performed at the Larmor frequency of a 3T scanner and in a WiFi wireless communication band to optimize the radius and position of an iRFW coil located near the head of a human model inside the scanner bore, which were validated by performing both imaging and wireless experiments. Main Results. The simulated iRFW coil with a 40 mm radius positioned near the model forehead provided: a signal-to-noise ratio (SNR) comparable to that of a traditional RF coil with the same radius and position, a power absorbed by the human model within regulatory limits, and a gain pattern in the scanner bore resulting in a link budget of 51.1 dB between the coil and an AP located behind the scanner 3 m from the isocenter, which would be sufficient to wirelessly transfer MRI data acquired with a 16-channel coil array. The SNR, gain pattern, and link budget for initial simulations were validated by experimental measurements in an MRI scanner and anechoic chamber to provide confidence in this methodology. These results show that the iRFW coil design must be optimized within the scanner bore for the wireless transfer of MRI data. Significance. The MRI RF coil array coaxial cable assembly connected to the scanner increases patient setup time, can present a serious burn risk to patients and is an obstacle to the development of the next generation of lightweight, flexible or wearable coil arrays that provide an improved coil sensitivity for imaging. Significantly, the RF coaxial cables and corresponding receive chain electronics can be removed from within the scanner by integrating the iRFW coil design into an array for the wireless transmission of MRI data outside of the bore.

Analysis and design of in-vessel magnetic compression coil system for HFRC

A field-reversed configuration (FRC) experiment facility HUST-FRC (HFRC) is being built at Huazhong University of Science and Technology, where the magnetic compression of FRC will be investigated. To generate a pulsed compression magnetic field, a compression coil system is under development, consisting of in-vessel compression coils, a pulsed power supply, and feedthroughs. Energized by the pulsed power supply, a large current peaking ∼110 kA within 50 μs is transferred to in-vessel compression coils across the feedthroughs. This article presents the analysis and design of the compression coil system. At first, field ripple optimizations are performed to reduce the axial and toroidal ripples within 5%, resulting in an optimized coil arrangement and an improved coil conductor structure. In addition, the power supply circuits are quite complex due to the strong electromagnetic couplings among the coils and between each coil and the metal chamber wall. To rapidly and accurately design the electrical parameters of the pulsed power supply for achieving the target coil currents, a decoupled optimization method based on a circuit-electromagnetic model and a decoupled equivalent circuit model is proposed. The errors of the coil currents and the magnetic field are within 1%. Lastly, a feedthrough design and an optimized feeder scheme are proposed to achieve the structural stability of the feedthroughs since they are subjected to large electromagnetic forces.

2-D Winding Losses Calculation for Round Conductor Coil

Winding loss calculation is essential for inductor and transformer design. In this article, a revised 1-D Ferreira's formula is proposed, which considers the interaction between conductors. Then, a 2-D loss calculation approach is proposed based on the analytical solution of round conductors under a uniform external field. An equivalent external magnetic field is calculated to estimate the winding losses, considering the impact of eddy current. The proposed approach is compared with the 2-D FEM with three types of windings and shows good accuracy with less than 10% error. 3-D FEMs and samples are built based on two simulated windings to validate the loss calculation.

Utility of a multipurpose catheter for transvenous extraction of old broken leads: A novel technique for fragile leads

Transvenous lead extraction has been possible since the 1980s. However, complications during lead extraction, such as the distal end fragment of the lead remaining in the myocardium or venous system and injury to the veins or heart, have been reported. The purpose of this study was to examine our method for complete removal of a separated lead, as extraction of long-term implanted devices is difficult using standard methods and may require additional procedures. The removal of leads with inner conductor coil and lead tip separated from outer insulation, conductor coil, and proximal ring electrode using a multipurpose catheter is reported. In total, 345 consecutive patients who underwent transvenous lead extraction (TLE) from April 2014 to March 2021 were retrospectively analyzed. Lead characteristics, device type, and indications for extraction were further analyzed in 20 patients who developed separation of the proximal ring electrode and outer conductor coil from the inner conductor and distal tip at the time of extraction. Extractions were performed using an excimer laser sheath laser and a Byrd polypropylene telescoping sheath (n = 15); laser, Byrd polypropylene telescoping sheath, and Evolution RL (n = 2); laser and Evolution RL (n = 3); Byrd polypropylene telescoping sheath and Evolution RL (n = 1); Byrd polypropylene telescoping sheath only (n = 4); and Evolution RL only (n = 2). Twenty-seven leads implanted for more than 10 years had lead separation. A multipurpose catheter was used to protect the fragile leads from further damage. All leads were completely extracted. All distal tip-to-proximal ring electrode separated leads were successfully removed using laser and other sheaths with the assistance of a multipurpose catheter, without any part of the leads remaining in the heart.

First performance test of FeSe0.5Te0.5-coated conductor coil under high magnetic fields

Iron-based superconductors have attracted intense interest from scientists around the world. The first FeSe0.5Te0.5 hybrid coil, including one FeSe0.5Te0.5 single pancake coil (SPC) and eight YBCO double pancake coils (DPCs), was successfully fabricated and tested in this study. The FeSe0.5Te0.5 tape used in the hybrid coil is encapsulated to strengthen the tape, and has a thickness of 0.15 mm and a width of 10.5 mm to withstand the high stress during the cold test. The FeSe0.5Te0.5 encapsulated tape exhibits good performance in the 4.2 K cold test. YBCO DPCs were divided into two groups connected to both sides of the FeSe0.5Te0.5 SPC. The critical current of the FeSe0.5Te0.5 coil was measured as the background field increased from 0 T to 10 T. The transport critical current of the FeSe0.5Te0.5 SPC was 108.1 A at self-field and 17.4 A at 10 T, which had almost the same performance as the FeSe0.5Te0.5 tape. The results of this study showed that the FeSe0.5Te0.5-coated conductor coil has good performance in high magnetic fields.

Embedded conductors in solidified molten metal for winding packs for high-field stellarators

The potential advantages of high-field stellarators are currently being recognised, as previously happened with tokamaks. However, the winding packs and the electrical insulation of the conductors in high-field stellarators require particularly high strength, and still keeping the dimensional accuracy and long-term positioning of the conductors in contorted coils. Radial plates in ITER, and stacked conductors with strong metallic jacket and internal insulation in FFHR heliotron have been validated and studied. However, radial plates for modular stellarators still require further studies and validation due the extreme accuracy required for the grooves in contorted plates, which increases with the number of turns per pancake.A third alternative is studied and experimented in this work. The concept implies casting a strong low-melting point metal in-between conductors, which are properly wound on a supporting structure. Thus, after solidification, the conductors (acting as inserts in a mould) and the metallic alloy act as a single solid structure. Essentially, the concept aims at relaxing the required accuracy in radial-plate grooves and to create a solid structure without spaces amongst conductors and without insulation external to the conductors. Therefore, a large number of conductors per winding pack may be created, which decreases certain stresses in the insulation and conductor. The drawbacks and difficulties found for this approach during the experiments with a scaled-down prototype are also presented and discussed.

Final Design of ITER In-Vessel Coils and Manufacturing of In-Vessel Coil Conductor

Following a decision made at the ITER Council in November 2013, two types of in-vessel coils (IVCs), namely, edge-localized mode (ELM) coils to mitigate ELMs and vertical stability (VS) coils to provide vertical stabilization of the plasma, have been incorporated in the ITER baseline design. The in-vessel environment is severe, characterized by large transient electromagnetic fields, high radiation flux, and high temperature. To withstand this environment and provide the required functionality, a “mineral insulated conductor” (MIC) technology has been selected for the IVC conductor. It consists of an axially water-cooled copper conductor surrounded by magnesium oxide insulation and a stainless steel jacket. A major advantage of the coil design is the choice of the same conductor material and dimensions for both VS and ELM coils, long conductor length which eliminates the need for any internal joints, and Cu welding for the joints between coils and feeders. In situ winding of the VS coils is asking for the development of a creative solution for the unspooling, straightening, precise winding tools, bending, forming, and metrology processes in a tight and congested environment. Mock-ups for design verification and manufacturing feasibility have been produced, in particular, for the bracket manufacture and to perform thermal and mechanical fatigue testing on an ELM control coil winding pack assembly. Installation trials of a half-size ELM control coil have been performed to verify the feasibility of the assembly procedure. This article will give an overview of the IVC design status and the progress of ITER IVC conductor manufacturing.

Effect of winding methods: transport AC losses in CORC coils

AC losses undoubtedly increase the burden on the cooling system and affect the overall performance of high-temperature superconducting (HTS) cables. Therefore, AC losses in HTS cables are important design factors for large-scale HTS equipments. Extensive research has been conducted on straight, densely wound conductors. However, AC losses of bending/circular HTS cable conductors have not been sufficiently studied. In this article, the transport AC losses in a circular HTS conductor coil bended by a conductor on round core (CORC) type cable were investigated using experiments and numerical simulations. The effect of different winding methods was also studied. First, the modeling method of the three-dimensional simulation and the experimental procedures were presented. The simulation results of the straight densely wound conductor (SDWC) and circular densely wound coil (CDWC) were compared with the corresponding experimental results. Finally, the winding method for the CDWC was optimized using both the simulation and experimental approaches. Both the experiments and simulations showed that reducing the tape-to-tape frontal area was able to decrease the transport AC loss, and the results show that the optimum winding angle of the HTS CORC coil was 24.15°. Overall, the modeling and experiments provide useful optimization strategies for designing winding structures of high-performance CORC coils/magnets.

Coupling electromagnetic numerical models of HTS coils to electrical circuits: multi-scale and homogeneous methodologies using the T-A formulation

Numerical simulation is an effective tool for predicting the electromagnetic behavior of superconductors. Recently, a finite element method-based model coupling the T-A formulation with an electrical circuit has been proposed: the model presents the superconducting constituent as a global voltage parameter in the electrical circuit. This allows assessing the overall behavior of complex high-temperature superconductor (HTS) systems involving multiple power items, while keeping a high degree of precision on the presentation of local effects. In this work, the applicability of this model has been extended to large-scale HTS applications with hundreds or thousands of tapes by referring to two widely recognized methodologies, multi-scale and homogenization, to improve the computation efficiency. Based on the two approaches, three different models were developed and their effectiveness was assessed using the case study of a 1000 turn cylindrical HTS coil charged by a DC voltage source. The comparison of the calculated global circuit parameters, local field distributions, losses, and computation time proves that the computation efficiency can be improved with respect to a model simulating all HTS tapes, without compromising accuracy. The results indicate that the developed models can therefore be efficient tools to design and optimize large-scale HTS devices used in electrical machines and power grids. It is also found that the inductance of an HTS coil is varied according to the transport current and can be even higher than that of a normal conductor coil with the same geometry. We attribute this result to the superconductor’s non-uniform current distribution and relaxation effect during the dynamic process.