Coil Conductor Research Articles

Construction and test of a non-insulated insert coil using coated conductor tape

A small coated conductor coil (central field 1 T at 200 A) was constructed and tested in order to evaluate the benefit and the possible disadvantages of non insulated, double pancake construction, in particular regarding quench protection. The insert coil consists of three double pancakes without turn to turn insulation, and it was impregnated with beeswax. The coil was equipped with voltage taps on each pancake, thermocouples and a quench heater. Quench tests were carried out because quench protection is one of the main issues in developing coil technology for coated conductors. Quenches were induced either by a heater or by exceeding the coil critical current; in all cases the quench protection system was able to detect the quench.

Multiturn surface coil: Theoretical considerations on unloaded to loaded Q ratio and SNR

ABSTRACTRadiofrequency coils in magnetic resonance systems are used for exciting the nuclei in the object to be imaged and for picking up the signals emitted by the nuclei. The quality of obtained images strongly depends on the correct choice of the coils geometry and type. Although the coils' performance are influenced by the cross‐sectional shape of the coil conductors, for multiturn surface coils proximity effects between conductors can significantly influence coil behavior. This work describes how the use of a multiturn conductor affects a coil's performance in terms of unloaded to loaded quality factors ratio and signal‐to‐noise ratio, taking into account for the proximity effect between conductors of the coil. © 2014 Wiley Periodicals, Inc. Concepts Magn Reson Part B (Magn Reson Engineering) 44B: 27–31, 2014

Challenges and status of ITER conductor production

Taking the relay of the large Hadron collider (LHC) at CERN, ITER has become the largest project in applied superconductivity. In addition to its technical complexity, ITER is also a management challenge as it relies on an unprecedented collaboration of seven partners, representing more than half of the world population, who provide 90% of the components as in-kind contributions. The ITER magnet system is one of the most sophisticated superconducting magnet systems ever designed, with an enormous stored energy of 51 GJ. It involves six of the ITER partners. The coils are wound from cable-in-conduit conductors (CICCs) made up of superconducting and copper strands assembled into a multistage cable, inserted into a conduit of butt-welded austenitic steel tubes. The conductors for the toroidal field (TF) and central solenoid (CS) coils require about 600 t of Nb3Sn strands while the poloidal field (PF) and correction coil (CC) and busbar conductors need around 275 t of Nb–Ti strands. The required amount of Nb3Sn strands far exceeds pre-existing industrial capacity and has called for a significant worldwide production scale up. The TF conductors are the first ITER components to be mass produced and are more than 50% complete. During its life time, the CS coil will have to sustain several tens of thousands of electromagnetic (EM) cycles to high current and field conditions, way beyond anything a large Nb3Sn coil has ever experienced. Following a comprehensive R&D program, a technical solution has been found for the CS conductor, which ensures stable performance versus EM and thermal cycling. Productions of PF, CC and busbar conductors are also underway. After an introduction to the ITER project and magnet system, we describe the ITER conductor procurements and the quality assurance/quality control programs that have been implemented to ensure production uniformity across numerous suppliers. Then, we provide examples of technical challenges that have been encountered and we present the status of ITER conductor production worldwide.

Accuracy of tidal breathing measurement of floright compared to an ultrasonic flowmeter in infants

Monitoring breathing pattern is especially relevant in infants with lung disease. Recently, a vest-based inductive plethysmograph system (FloRight®) has been developed for tidal breathing measurement in infants. We investigated the accuracy of tidal breathing flow volume loop (TBFVL) measurements in healthy term-born infants and infants with lung disease by the vest-based system in comparison to an ultrasonic flowmeter (USFM) with a face mask. We also investigated whether the system discriminates between healthy infants and those with lung disease. Floright® measures changes in thoracoabdominal volume during tidal breathing through magnetic field changes generated by current-carrying conductor coils in an elastic vest. Simultaneous TBFVL measurements by the vest-based system and the USFM were performed at 44 weeks corrected postmenstrual age during quiet unsedated sleep. TBFVL parameters derived by both techniques and within both groups were compared. We included 19 healthy infants and 18 infants with lung disease. Tidal volume per body weight derived by the vest-based system was significantly lower with a mean difference (95% CI) of -1.33 ml/kg (-1.73; -0.92), P < 0.001. Respiratory rate and ratio of time to peak tidal expiratory flow over total expiratory time (tPTEF/tE) did not differ between the two techniques. Both systems were able to discriminate between healthy infants and those with lung disease using tPTEF/tE. FloRight® accurately measures time indices and may discriminate between healthy infants and those with lung disease, but demonstrates differences in tidal volume measurements. It may be better suited to monitor breathing pattern than for TBFVL measurements.

Research on electromagnetic efficiency optimization in the design of air-core coils

Summary In this paper, the electromagnetic efficiency factor is defined to describe the utilization rate of metal conductors in air-core coils. The geometry-electromagnetic character and the thermal condition of the coil are coupled to describe the electromagnetic efficiency of the air-core coils. The geometry-electromagnetic character is deduced form the inductance computation formula, while the thermal functions are given according to the “Uniformed electrical current density condition” and the “uniformed temperature rise” condition. Curves that reflect the electromagnetic efficiency factor are given while the thermal condition is considered as the mentioned two conditions. The former thermal condition is simpler and is proved to be suitable for midget air-core coils without complex heat transfer structure or coils with pulse current. While, the latter is proved to be with higher accuracy and can be wildly used in the optimization design of air-core power reactors. Copyright © 2014 John Wiley & Sons, Ltd.

A design tool for magnetic resonance imaging gradient coils using DUCAS with weighted nodes and initial current potentials

DUCAS is a computer code using an arbitrary magnetic field distribution as input and producing a sheet current distribution as output. The code was improved for application to the magnetic resonance imaging (MRI) gradient coil (GC) design. DUCAS computes the current potential (CP) distribution, and the coil conductors are placed along the contours, which are current flow lines. An improved algorithm with weights on node CPs and input initial CPs is described for use with DUCAS. The algorithm obtains the CP distribution by summing singular value decomposition (SVD) eigendistributions with the initial CP distribution. The weights modify the eigendistributions. The initial CP distribution is used to get smooth flow lines and then coil patterns. The improved DUCAS is suitable for avoiding a complex current distribution and to obtain coil patterns that are easy to manufacture. The initial CP distribution is assumed first, then DUCAS compensates the CPs for the given magnetic field distribution with the weights. This paper describes the computational algorithm and shows a GC design obtained with it.

Electromagnetic Forces of High-T c Superconducting Coated Conductor Coils Subjected to Sinusoidal Traveling Magnetic Fields

In order to optimize the structure of high temperature superconducting coils for linear motor applications, three separate coils with different shapes made of Re-BCO coated conductor were studied: circular shaped single pancake, circular shaped double-pancake and racetrack shaped single-pancake. The thrust and vertical forces of the three coils above a conventional flat linear three-phases winding were investigated experimentally. With the aid of the experimentally obtained values, it was found that single-pancake coil in the shape of a racetrack was the best selection for a flat single-sided linear motor system. Studies were also made on the frequency characteristics of the vertical force of the racetrack shaped single-pancake coil.

Calculation of AC loss in coated conductor coils with a large number of turns

For superconducting coils with many turns, it is widely believed that the magnetic field from magnetization currents is negligible compared with the one generated by the whole coil. This paper shows that this is not the case, from a few turns up to a considerable number of turns (thousands). We introduce a method to accurately calculate the AC loss in coils with virtually any number of turns that takes the magnetization currents into account. The current density and AC loss are analyzed for two windings made of a coated conductor consisting of a stack of 32 pancake coils totaling 768 and 6400 turns, respectively.

Stress and Thermal Analysis of the In-Vessel RMP Coils in HL-2M

A set of in-vessel resonant magnetic perturbation (RMP) coils for MHD instability suppression is proposed for the design of a HL-2M tokamak. Each coil is to be fed with a current of up to 5 kA, operated in a frequency range from DC to about 1 kHz. Stainless steel (SS) jacketed mineral insulated cables are proposed for the conductor of the coils. In-vessel coils must withstand large electromagnetic (EM) and thermal loads. The support, insulation and vacuum sealing in a very limited space are crucial issues for engineering design. Hence finite element calculations are performed to verify the design, optimize the support by minimizing stress caused by EM forces on the coil conductors and work out the temperature rise occurring on the coil in different working conditions, the corresponding thermal stress caused by the thermal expansion of materials is evaluated to be allowable. The techniques to develop the in-vessel RMP coils, such as support, insulation and cooling, are discussed.

Design and Numerical Analysis of Non-Uniform Electromagnetic Field Based on the Wedge Magnetic Pole

As there are relatively fewer studies about non-uniform magnetic field design and numerical analysis, a model of wedge pole electromagnet has designed and analyzed based on the traditional electromagnet design method. The effects of coil turn, conductor sectional and electric current density on magnetic field intensity had also designed and calculated. The design and numerical analysis of wedge pole electromagnet were conducted which adopted the finite element simulation and optimal design method. The magnetic induction intensity for the wedge pole electromagnet in different positions of the air gap had analog calculated. The simulated and test results for distributing magnetic field can be well corresponded by considering the effect of eddy loss, material and machining errors of electromagnetic. The result indicated that the method of simulation is correct and practical. The method provides a reliable simulation analysis and empirical data for the design of non-uniform magnetic field.

Investigation and analysis on ITER in-vessel coils’ raw-materials

The ITER in-vessel coils (IVCs) consist of 27 coils edge localized modes (ELM) and 2 coils vertical stabilization (VS) which are all mounted on the vacuum vessel wall behind the shield modules. The IVCs design and manufacturing work is being conducted in between Institute of Plasma Physics Chinese Academy of Sciences (ASIPP) and Princeton Plasma Physics Laboratory (PPPL). Because the position of ELM and VS coils is close and face to the plasma, the IVCs must undergo a severe environment, such as the high dose of radiation and high operation temperature, thus the conventional electrical insulation materials cannot be used. And the technology of “Stainless Steel Jacketed Mineral Insulated Conductor” (SSMIC) is deemed as the best choice to provide the necessary radiation resistance and compatibility strength in ITER's vacuum vessel. While mineral insulated conductor technology is not new, and is similar to the mineral insulated cable used in industrial. Some difficulties still need to be solved, such as searching for the proper raw-materials to make sure that the conductor have the properties of high current carrying capability, the necessary radiation resistance, the proper strength, at the same time, it must be come true in manufacture technology. This paper described the analysis of the materials for VS and ELM coil conductor.

An ultra-thin polyimide insulation coating on REBCO conductors by electrodeposition produces a maximum overall current density for REBCO coils

One apparent shortcoming of REBCO conductor coils is an extremely low fraction of conductor in the coil winding, as the REBCO conductor is as thin as 100–150μm, comparable to the insulation thickness. If we wish to achieve high overall current densities for REBCO coils, the insulation thickness on REBCO conductor must be substantially reduced. Therefore, we have developed a 4μm thick ultra-thin polyimide insulation coating by electro-deposition, which is 10-fold-thinner than conventional insulations on REBCO conductors. The fraction of REBCO conductor in the coil winding manufactured by this novel conductor becomes as high as 90%, which is comparable to that for a low temperature superconducting coil winding manufactured from Formvar-coated NbTi conductor. Thus, one important shortcoming of REBCO coils is satisfactorily overcome by using ultra-thin polyimide coated conductors, making possible a dramatic increase in the overall current density of such coils.

Early fatigue fractures in the IS-1 connector leg of a small-diameter ICD lead: Value of returned product analysis for improving device safety

Conductor fractures may affect the performance of implantable cardioverter-defibrillator leads. During routine surveillance of returned product analyses (RPAs) in the Food and Drug Administration's Manufacturers and User Facility Device Experience database, we found a number of conductor fractures in small diameter implantable cardioverter-defibrillator leads manufactured by St Jude Medical, Inc (SJM, Sylmar, CA). To determine the location and cause of these fractures and to catalog their clinical signs and consequences. We searched the FDA's Manufacturers and User Facility Device Experience database on April 11, 2013. SJM provided information and data it collected independently. Our search found 59 leads with fractures in the IS-1 leg. Most fractures were in leads implanted in 2008-2009; no fractures were found in leads implanted after 2010. Outer coil conductor fractures accounted for the majority (51 of 59, 86%). Oversensing and noise were common signs, and 81% of the patients received inappropriate shocks. SJM's RPAs found that the fractures were due to inadequate strain relief and redesigned the IS-1 leg by shortening the crimp bore. Younger age and subpectoral implants appeared to be associated with these fractures. SJM stated the incidence is low (0.040%) and has not seen further fractures of this type in leads with the modified crimp. SJM's small diameter leads that were manufactured before 2011 are prone to early outer coil fatigue fractures in the IS-1 leg. The failure mechanism appears to have been mitigated by a design change. RPA is important for improving device safety.

Manufacturing of the ITER TF Conductors in China

The toroidal field (TF) coil conductor is a cable-in-conduit conductor made up of superconducting, Nb3Sn-based strands mixed with pure copper strands. The strands are assembled in a multistage cable around an open central spiral. The cable and its spiral are inserted into a stainless steel jacket. The jacket provides the helium confinement and must conform to the leak tightness standard defined herein. A technological complex has been developed at the Institute of Plasma Physics Chinese Academy of Sciences for serial production of ITER TF conductors is described. This technology was developed as a result of performing some R&D programs on selecting cabling parameters, welding technology, elaboration of cable insertion, compaction, and winding process. One qualification dummy TF conductor (760 m) and superconducting conductor (110 m) were successfully made. A new manufacturing complex was developed within the Institute of Plasma Physics Chinese Academy of Sciences for realization of this technology. The details of manufacturing procedures are described in this paper. It consists of a cabling workshop, and jacketing line equipped with full production machinery and test devices.

2G HTS Coil Technology Development at SuperPower

The second-generation high-temperature superconductor (2G HTS), Re-Ba-Cu-O coated conductors are known for strong mechanical properties and have numerous potential applications in high magnetic field research and electrical power systems. It has been noted in the community that coated conductors can be prone to performance degradation on thermal cycling when used in epoxy impregnated magnet windings. This degradation has been tied to the <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">c</i> -axis peel strength in the wire. SuperPower is addressing this issue with a short term approach of developing novel technologies in conductor post processing and coil winding technology, which allows building high quality coils with current generation conductor, and a longer term approach of improving wire production to build stronger wire with high <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">c</i> -axis peel strength.

Stress dependence of the critical currents in neutron irradiated (RE)BCO coated conductors

The application of HTS coated conductors in future fusion or accelerator magnets is currently of increasing interest. High Lorentz forces and therefore high hoop stresses act on the conductors in large coils. The conductor is furthermore exposed to neutron radiation in fusion or accelerator magnets. The expected neutron fluence over the desired lifetime of such magnets can be simulated by irradiation experiments in a fission reactor. The coated conductors were characterized in the pristine state and after irradiation to a fast neutron fluence of 1 × 1022 m−2 (ITER design fluence). The sensitivity of the critical currents to applied stress was measured in liquid nitrogen. The cold part of the setup was positioned within a rotatable split coil electro-magnet to assess the Ic-anisotropy up to 1.4 T under maximum Lorentz force configuration. The Ic-sensitivity to applied stress changed significantly in the GdBCO/IBAD conductor after irradiation, whereas nearly no change was observed in the YBCO/RABiTS conductor. Furthermore, Ic and Tc were strongly reduced in the GdBCO/IBAD sample after irradiation. The angular dependence of Ic changed for both samples in different ways after the irradiation, but no change in the angular dependence was observed upon applying stress. The high neutron capture cross-section of Gd and the resulting strong reduction of Tc seem to be responsible for the different stress dependences of Ic in irradiated Gd-123 coated conductors.

Malfunction of Cardiac Resynchronization Therapy due to Subsequent Fracture of the Ring and Tip Conductors of a Co-radial Left Ventricular Bipolar Lead

In two patients treated with cardiac resynchronization therapy (CRT), left ventricular (LV) pacing failure occurred due to ring conductor fractures of the bipolar LV lead (co-radial model). CRT was resumed by pacing between the tip conductor of the LV lead and the coil conductor of the right ventricular lead. However, shortly thereafter, subsequent fracture of the tip conductor developed, and implantation of a new LV lead was required. When one of the bipolar conductors of a co-radial designed LV lead fractures, reimplantation of a new LV lead is a better therapeutic option (than changing the LV pacing mode) in order to reliably continue CRT treatment.

Characterisation of electromagetic welding equipment

The paper describes the procedure for selection of electromagnetic parameters which govern the Electromagnetic Welding (EMW) process. EMW is a specific application of electromagnetic Forming (EMF). The metallic bodies get deformed and eventually collide to get welded. Hence it is classified as deformation bond. It is observed that the parameters such as input electrical energy, ringing frequency, coil geometry, coil conductor section, job material and it's configuration play a very important role in achieving the welding. In addition to this, the separation distance between the two colliding bodies (plates in the present case) is also a crucial parameter. These parameters together decide the resultant collision velocity. The collision velocity in turn decides the strength of weld joint. The procedure is formulated based on computational and experimental observations as applied to 1 and 2 mm thick aluminium plates. This procedure could be extended for other materials and their combinations (such as similar or dissimilar and of different dimensions).

A Vibration-Based Hybrid Energy Harvester for Wireless Sensor Systems

Vibration energy harvesting has been receiving a considerable amount of interest as a means of powering wireless sensors and low power devices. In this paper, a novel hybrid energy harvester integrated with piezoelectric and electromagnetic energy harvesting technique is investigated. It consists of a cantilever beam bonding with two piezoelectric plates for piezoelectric energy conversion, and a permanent magnet attached on the end of the beam as a tip mass for inspiring the vibration and adjusting the resonance frequency, at the same time relative motion of the magnet with a conductor coil induces an electromotive force in the coil. An analytical model is developed to analyze the nonlinear vibration and electrical output performances of the harvester. A prototype is fabricated and tested. The experimental results show close agreement with the analytical results in trend. The maximum of load power of the hybrid harvester achieves 10.7 mW on the optimal load resistance of 50 Ω at the resonant frequency of 50 Hz with the acceleration of 0.4 g, which is increased by 81.4% compared with 5.9 mW of the single electromagnetic technique.

Test Results of ITER Correction Coil Short Samples CCCN1 and CCCN2

This paper presents the first benchmarking test results of ITER correction coil (CC) conductor short samples CCCN1 and CCCN2. The Chinese first CC conductor short sample CCCN1 was prepared and tested at the Institute of Plasma Physics, Chinese Academy of Sciences (ASIPP). The second CC conductor short sample CCCN2 was prepared at ASIPP and tested at the SULTAN laboratory. The TCS of the two samples was measured at the peak magnetic field of 4.1 T and at a current of 10 kA. A TCS of 7.02 K was measured at ASIPP and a TCS of 7.20 K was measured at the SULTAN laboratory. The calculated results of the short samples are also presented for a comparison to the measured results in this paper.