Solenoid Coil Wound Research Articles

Differential behavior of magnetic field and magnetic vector potential in an optically pumped Rb atomic magnetometer

Although vector potentials are more intrinsic physical quantities than magnetic and electric fields, measuring them macroscopically is difficult. A double-nested Helmholtz-type vector potential coil, consisting of an elongated solenoid coil wound around a cylinder, and producing a uniform magnetic vector potential, was developed in this study. The coil is carefully designed to reduce the influence of the leakage magnetic field and the scalar potential generated by the coil’s electrical resistance on the measurement. It has the ability to toggle between vector potential and magnetic field generation. We adapted the coil for use in an optically pumped atomic magnetometer. We also developed an optically pumping Rb atomic magnetometer that can calibrate in a zero magnetic field and applied a time-varying magnetic vector potential. We found that the output signal changed with the vector potential even when there was virtually no magnetic field. With increasing frequency, the output voltage decreases for the magnetic signal and increases for the magnetic vector potential signal. The results revealed that the atomic magnetometer is influenced not only by the magnetic field but also by the magnetic vector potential and that the frequency responses are opposite.

Performance of Compact Wind-and-React MgB2 Solenoid Coil Made With Continuously Produced Cable

MgB <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> superconducting wires hold the advantage over traditional NbTi wires of higher temperature operation, at lower cost than high temperature superconductors, and allowing the use of existing winding techniques. The adoption of MgB <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> wires into large-scale applications requires a robust production process yielding long length wires with consistent performance. Bekaert and Epoch wires have developed a scalable powder-in-tube technique capable of producing MgB <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> wires in km lengths. Demonstrating practical current density in a solenoid coil is an essential step towards larger demonstration assemblies and coils, in wind-and-react or react-and-wind configurations. Here, we report on the performance of a compact wind-and-react solenoid coil wound from Bekaert/Epoch wires 1+6 MgB <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> cable, made up of unstabilized, monocore 0.4 mm MgB <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> wires. The coil was tested in a He-vapor cooled VTI inside a 10 T Cryofree magnet, between 10 K and 20 K, and at up to 3 T background field. The coil reached 384 A at 15 K in zero external field, generating a self-field of 1.88 T without quench. The coil was quenched multiple times without damage.

Shielding currents in multifilament coated conductors wound into pancake coils and layer-wound coils

The effect of multifilament coated conductors on reducing shielding currents was studied by numerical electromagnetic field analyses. We compared the behaviours of the shielding currents in stacked double pancake coils and layer-wound solenoid coils (SLCs) wound with the following conductors: a monofilament coated conductor, a copper-plated two-filament coated conductor, and an insulated two-filament coated conductor. Shielding-current-induced fields (SCIFs) in the layer-wound SLCs wound with copper-plated two-filament coated conductors decay more rapidly than in stacked double pancake coils wound with copper-plated two-filament coated conductors. In addition, we examined the behaviour of the shielding currents in the coils with and without normal metal terminals. The normal metal terminals made the decay time constants of the SCIFs in pancake coils longer, while the decay time constants of SCIFs did not change notably in the layer-wound SLCs with and without normal metal terminals.

Magnetization Loss Estimation of HTS Solenoid Coils Wound With CORC

CORC is one of the candidates of the HTS cable for high field magnets. We have been interested in applying CORC to HTS power transformers that require not only large currents but also very low AC losses. Striation and twisting are the solutions for reducing AC losses. We suggested an estimation method for a rough calculation of magnetization losses in a striated CORC coil. First, we measured and calculated the magnetization losses of short samples of straight CC tapes and CORC. Before considering the striation effect, we analyzed the characteristics of slit HTS tapes. In order to emulate the slitting of an HTS tape, we prepared three kinds of HTS tapes with different widths: 2, 4, and 6 mm. Slitting will certainly create the effect of reducing the magnetization loss, but the effect is not directly dependent on the number of the slits nor the applied field magnitude. We measured and compared the magnetization losses of a wide HTS tape to those of narrow HTS tapes. And the narrow tapes were arranged in parallel and measured, so the net width was same as the width of the wide tape. Finally, we applied the measured data of the magnetization loss of several samples to the calculation of the losses of solenoid coils wound with CORC in order to take into account the loss reduction effect of slit HTS tapes.

Theoretical evaluation of the screening-current-induced magnetic field in superconducting coils with tape wires

We theoretically investigate the physical mechanism of the screening-current-induced field (SCIF) in solenoid coils wound with superconducting tape wires. We derive the direct relationship between the SCIF and the magnetization of tape wires, and a scaling law for the SCIF and the coil dimensions is demonstrated. A simple analytical expression of the SCIF is obtained as functions of current load factor, tape wire width, and the coil dimensions. We verify that the published data for the precise numerical computation of SCIF are roughly fitted by our theoretical results for flat coils where the height is smaller than the outer diameter.

Monitoring of Non-Ferrous Wear Debris in Hydraulic Oil by Detecting the Equivalent Resistance of Inductive Sensors.

Wear debris in hydraulic oil contains important information on the operation of equipment, which is important for condition monitoring and fault diagnosis in mechanical equipment. A micro inductive sensor based on the inductive coulter principle is presented in this work. It consists of a straight micro-channel and a 3-D solenoid coil wound on the micro-channel. Instead of detecting the inductance change of the inductive sensor, the equivalent resistance change of the inductive sensor is detected for non-ferrous particle (copper particle) monitoring. The simulation results show that the resistance change rate caused by the presence of copper particles is greater than the inductance change rate. Copper particles with sizes ranging from 48 μm to 150 μm were used in the experiment, and the experimental results are in good agreement with the simulation results. By detecting the inductive change of the micro inductive sensor, the detection limit of the copper particles only reaches 70 μm. However, the detection limit can be improved to 48 μm by detecting the equivalent resistance of the inductive sensor. The equivalent resistance method was demonstrated to have a higher detection accuracy than conventional inductive detection methods for non-ferrous particle detection in hydraulic oil.

Simulations and Experiments for the Detection of Flow-Assisted Corrosion in Pipes

Flow-accelerated corrosion (FAC) is a phenomenon which causes wall thinning of pipes, fittings, vessels, and other components in the metal based piping systems that carry water or water-steam mixture in power plants and refineries. Currently used nondestructive techniques, such as radiographic testing (RT), ultrasonic testing (UT), and pulsed eddy current (PEC) testing in order to determine the remaining wall thickness, are time consuming and not economical. Hence, in this work, the use of the fundamental torsional mode ultrasonic guided wave to detect FAC was investigated using the finite element method (FEM) simulations and that were validated with experiments. The torsional wave was generated by the magnetostriction principle using surface mounted strips made of magnetostrictive Hyperco (FeCo) material that provided the source for the surface tractions required to generate the ultrasonic guided wave. The transient electric field was provided through a solenoid coil wound over the strips and permanent magnets were employed to provide the bias magnetic field. From this work, it was observed that the pulse-echo method is not suitable for the FAC detection because of the insignificant reflections from FAC defect region that could not be effectively detected. The through-transmission method was found to be more suitable for the FAC detection because the amplitude of transmitted signal decreased with increase in radial depth of FAC in both the simulation and experiment.

Designs and Tests of Shaking Coils to Reduce Screening Currents Induced in HTS Insert Coils for NMR Magnet.

Two types of shaking coils are focused on reducing screening currents induced in solenoid coils wound with high-temperature superconducting (HTS) tapes. One is a pair of copper shaking coils coaxially located inside and outside the HTS coil to apply an ac magnetic field in the axial direction. The other is an HTS shaking coil with notch located only outside the HTS coil to minimize the radial components of local ac fields applied to windings of the HTS coil as small as possible. It is found that the copper shaking coils yield the allowable amount of power dissipation in liquid helium. The effectiveness of the HTS shaking coil to reduce screening-current-induced fields generated by another magnetized HTS coil is also experimentally validated in liquid nitrogen using a commercially available coated conductor with narrow width.

Development of a New High Sensitive Eddy Current Sensor

Eddy current testing (ECT) is one of the most representative nondestructive testing methods for metallic materials, parts, structures and so on. Operating principle of ECT is based on two major properties of the magnetic field. One is that alternating magnetic field induces eddy current in conducting materials. Thereby, an input impedance of the magnetic field source, i.e., electric source, depends on the eddy current path. Second is that the magnetic field distribution depends not only on the exciting but also on the reactive magnetic fields caused by the eddy currents in targets. Former and latter are the impedance sensing and magnetic flux sensing types, respectively.This paper concerns with an optimization of a new magnetic flux sensing type sensor named coil. Exciting and sensing coils are composed of shape coil and a finite length solenoid coil wound on ferrite bar, respectively. Development of this coil fully depends on the 2D and 3D finite elements method modeling. According to the simulation results, we have worked out two types of coils. Practical experiments reflect the validity of both simulation and design aims, quite well. Thus, we have succeeded in developing coil having a higher sensibility compared with that of conventional one.

A Suitable Design Method of SMES Coil for Reducing Superconducting Wire Usage Considering Maximum Magnetic Flux Density

Generally, high magnetic flux density is adopted in superconducting magnetic energy storage (SMES) coil design to reduce superconducting coil size and increase energy density. However, critical current density of the SMES coil is degraded by applying the high magnetic flux density to superconducting wire. This means that adopting the high magnetic flux density is not necessarily suitable for the superconducting wire reduction of the SMES coil. In this paper, the relationship between the maximum magnetic flux density within coil and superconducting wire usage of the SMES coil composed of solenoid or toroidal coil wound by MgB2, Bi2223, or REBCO wire was investigated. As a result, most suitable magnetic flux density within SMES coil for realizing the minimum superconducting wire usage in MgB2 , Bi2223, and REBCO wires were clarified. How to estimate the most suitable maximum magnetic flux density within coil for realizing the minimum wire usage in each superconducting wire was also investigated. Comparison between the rate of change of coil radius times maximum magnetic flux density and critical current density with respect to the maximum magnetic flux density is useful for obtaining the suitable maximum magnetic flux density for the minimum superconducting wire usage.

Electromagnetic Field Analyses of REBCO Roebel Cables Wound Into Coil Configurations

We have been developing a model for numerical electromagnetic field analyses of REBCO Roebel cables wound into coil configurations, considering their three-dimensional structure. Electromagnetic field analyses were carried out for one-turn circular closed loop of a Roebel cable, one turn circular closed loop of a Roebel cable at the end of a stack of Roebel-cable loops which simulated a solenoid coil of a finite length, and an infinite solenoid coil wound with a Roebel cable. From the temporal evolution of the current distribution in the Roebel cables, ac losses were calculated. We studied the ac loss characteristics of Roebel cables in different locations in coils. The influence of the gap between turns on ac losses was discussed.

A compact high-performance low-field NMR apparatus for measurements on fluids at very high pressures and temperatures

We discuss an innovative new high-performance apparatus for performing low-field Nuclear Magnetic Resonance (NMR) relaxation times and diffusion measurements on fluids at very high pressures and high temperatures. The apparatus sensor design and electronics specifications allow for dual deployment either in a fluid sampling well logging tool or in a laboratory. The sensor and electronics were designed to function in both environments. This paper discusses the use of the apparatus in a laboratory environment. The operating temperature and pressure limits, and the signal-to-noise ratio (SNR) of the new system exceed by a very wide margin what is currently possible. This major breakthrough was made possible by a revolutionary new sensor design that breaks many of the rules of conventional high pressure NMR sensor design. A metallic sample holder capable of operating at high pressures and temperatures is provided to contain the fluid under study. The sample holder has been successfully tested for operation up to 36 Kpsi. A solenoid coil wound on a slotted titanium frame sits inside the metallic sample holder and serves as an antenna to transmit RF pulses and receive NMR signals. The metal sample holder is sandwiched between a pair of gradient coils which provide a linear field gradient for pulsed field gradient diffusion measurements. The assembly sits in the bore of a low-gradient permanent magnet. The system can operate over a wide frequency range without the need for tuning the antenna to the Larmor frequency. The SNR measured on a water sample at room temperature is more than 15 times greater than that of the commercial low-field system in our laboratory. Thus, the new system provides for data acquisition more than 200 times faster than was previously possible. Laboratory NMR measurements of relaxations times and diffusion coefficients performed at pressures up to 25 Kpsi and at temperatures up to 175 °C with crude oils enlivened with dissolved hydrocarbon gases (referred to as "live oils") are shown. This is the first time low-field NMR measurements have been performed at such high temperatures and pressures on live crude oil samples. We discuss the details of the apparatus design, tuning, calibration, and operation. NMR data acquired at multiple temperatures and pressures on a live oil sample are discussed.

Analysis of the Operational Characteristics of a Resistive SFCL by Using the YBCO Coated Conductor

This paper deals with analysis of the operational characteristics of a resistive non-inductive winding type based superconducting fault current limiter (SFCL) by using YBa2Cu3Oy (YBCO) coated conductor (CC), and its characteristics are analysed through experiments. A non-inductive winding type SFCL system has non-inductive solenoid type coils wound with the YBCO CC and each coil has four windings of the CC in opposite direction to cancel off each inductance, connected in parallel each other. In the experiment, a resistive SFCL was developed and the short circuit test was performed during 0.1 s. The load was pure resistance and the fault switch was closed when a fault occurs. In order to measure the current, shunt resistance was used. A hall sensor was installed in the center of the SFCL to investigate the non-inductivity. The experimental results are given with the theoretical predictions by using finite difference method (FDM). This analysis is expected to be used in the electrical circuit application as well as the SFCL.

Ac Loss and Thermal Runaway of 1 T Cryocooler-Cooled Oxide Superconducting Pulsed Coil

We fabricated a 1 T cryocooler-cooled oxide superconducting pulsed coil. It is a 16-layer solenoidal coil wound with an interlayer-transposed 4-strand parallel conductor composed of Bi-2223 multifilamentary flat wires. The insulated strands were transposed only between layers to make all strands inductively equivalent. To suppress the temperature rise due to the AC loss, the aluminum nitride (AlN) plates were arranged between layers as heat drains. The pulsed coil was cooled down to 30 K by a single stage cryocooler. It can be operated continuously at 40 K in the 1 T triangular wave operation at 1 Hz. First we studied the temperature dependence of thermal runaway current of the coil under the application of direct transport current. The runaway current was higher than the critical current, which was defined as the current where the electric field of 10/sup minus;4/ V/m was generated on average over the whole length of the conductor. Next we studied the temperature variation of the coil in a sinusoidal operation of 1 Hz. The temperature increment was much more gradual than that in the DC operation. In this paper, we discuss the thermal properties of the cryocooler-cooled oxide superconducting pulsed coil, taking into account the heat generation of AC loss and flux-flow loss and the cooling capacity of a cryocooler.

Poynting vector method: AC loss measurement of long HTS tapes or wires wound into a solenoidal-coil

A new electrical system was developed for measuring ac losses of long HTS tapes or wires wound into a solenoidal-coil. This coil-loss measuring-system is an extension of our original ac-loss measuring system that is applicable to short, straight HTS tapes under various external conditions of transport currents and transverse magnetic fields, and is useful for fundamental studies of various windings of practical multi-layered coils. In this new system, the Poynting vectors at the outer and the inner surfaces of the coil were measured to get ac loss values by using two movable sets consisting of both a potential lead pair and a pick-up coil on each surface of the coil. The moving direction is the coil axis and its distance is one pitch of coil windings. The value of ac losses can be obtained by summation of the Poynting vector at many positions during the movement. The applicability of this system was confirmed by ac loss measurements on a solenoidal-coil wound loosely with Ag-sheathed, multifilamentary Bi-2223 tapes.

Effect of impedance distributions on current imbalance in insulated multi-stranded superconducting conductor

We have been investigating a current imbalance in multi-strand cable conductor using several types of solenoid coils wound by insulated multi-stranded copper cable, and obtained a result that the current distribution in the multi-stranded conductor is strongly affected by the magnetic coupling coefficient between strands. This time, we have carried out an experiment to investigate the current imbalance problem using a superconducting cable conductor. The main purpose of this investigation is to make clear the relation between the current imbalance and the impedance distributions among the strands. The experiment was carried out on (1) DC test, and (2) AC test. The calculation results show that the resistance component becomes dominant in the frequency region lower than 0.1 Hz. On the other hand, inductance component becomes dominant in the frequency region higher than 1 Hz. For the experimental results lower than 1 Hz, the amplitude and the phase characteristics of the current in each strand coincide well with the calculated results based on the measured resistance and impedance distribution. From these results, it can be concluded that a precise impedance measurement utilizing high accuracy LCR meter can estimate the current imbalance in insulated multi-stranded superconducting cable conductor before actual superconducting operation.

ITER niobium-tin strands reacted under model coil heat-treatment conditions

Heat-treatment conditions were studied for ITER Central Solenoid model coils wound with Nb/sub 3/Sn cables jacketed in Incoloy-908 conduits. The heat treatments recommended by the strand manufacturers had to be modified to meet various requirements for the large coils and to prevent Stress Accelerated Grain Boundary Oxidation (SAGBO) of Incoloy 908. Single-strand tests of ITER wires produced by Vacuumschmelze, IGC, Furukawa and Mitsubishi were carried out prior to the model coil heat treatments to verify the heat-treatment conditions. The modified heat treatments improved the performance of all four wires. Especially, critical currents of Furukawa wire were improved significantly. Test results of the witness samples co-reacted with ITER CS coils indicate that the heat treatments of all 10 layers of the inner module were successfully completed.

Development of a magnetic linear motor based on a friction drive

A new type of magnetic linear actuator based on a friction drive is presented. It consists of a magnet mover with inclined legs and a solenoid coil wound around a pipe. An alternating magnetic field produced by the coil causes the magnet to vibrate angularly due to magnetic torque and then the vibration is converted to a linear movement through friction between the legs and the stator wall. The prototype exhibited the maximum velocity of 33 cm/s and the maximum thrust of approximately 0.05 N around the mechanical resonant frequency.

Limited-sample NMR using solenoidal microcoils, perfluorocarbon plugs, and capillary spinning.

This study demonstrates three improvements to mass-limited NMR using solenoidal microcoils as detectors: (1) sample confinement using liquid perfluorocarbon plugs to increase the observe factor, (2) design and incorporation of a capillary spinner to improve spectral line widths, and (3) facile sample changing via the use of a capillary insert. The probe is constructed to spin a fused silica capillary of 530 microns i.d., 700 microns o.d. inside a solenoidal coil wound around a 0.8 mm i.d., 1 mm o.d. glass capillary. The smaller capillary contains the sample, and capillaries with different samples can be exchanged easily. In high-resolution limited sample microcoil NMR studies published thus far, the length of the sample plug has been 7-10 times the length of the solenoid to avoid line broadening from volume magnetic susceptibility (chi v) mismatches at both ends of the sample. This arrangement is not efficient since it places most of the sample volume outside of the coil observe volume. It is shown here that the observe factor cannot exceed 23% if the sample plug is bracketed by air, without substantial line broadening occurring. However, if the sample is bracketed by two liquid perfluorocarbon plugs, the observe factor can be increased to 70% while maintaining high spectral resolution. This is equivalent to improving the limit of detection by a factor of 3, or reducing the total data acquisition time for a given signal-to-noise by a factor of 9. It is also shown that, for the 440-nL sample plug used in this study (bracketed by the perflurocarbon plugs), sample spinning can improve the spectral resolution from 1.5 (nonspinning) to 0.6 Hz (spinning). This corresponds to a further improvement in the limit of detection of 2.5, or just over a factor of 6 decrease in data acquisition time.

Conceptual design of the ATLAS thin superconducting solenoid magnet

A thin superconducting solenoid has been designed to be installed into one of the major colliding particle detecting facilities, ATLAS, for LHC (Large Hadron Collider) project at CERN. The thin solenoidal coil wound with stiffened aluminum stabilized superconductor is indirectly cooled by forced two-phase helium through one serpentine tube on the outer support cylinder. The coil is installed into a common vacuum vessel with another co-axial cryogenic component, LAr-Cal, to save the wall material to trajectories for particles. Triangle-shape supporting elements on both ends of the coil are newly introduced to reduce a radial thickness of the cryostat.