Saddle-shaped Coil Research Articles

Development of a 5-Axis Winding Method for Saddle-Shaped Coils Using Coated ReBCO High Temperature Superconductors

Development of a 5-Axis Winding Method for Saddle-Shaped Coils Using Coated ReBCO High Temperature Superconductors

Design of cylindrical saddle-shaped transverse gradient coils with small aspect ratios and high linearity for micro comagnetometers

Design of cylindrical saddle-shaped transverse gradient coils with small aspect ratios and high linearity for micro comagnetometers

Design of a Conduction-Cooled Open Gradient Superconducting Magnetic Separation Magnet

Magnetic separation of wastewater is required to solve the problem of water pollution caused by a large amount of wastewater discharge in urbanization and industrialization. Superconducting magnets reduce energy consumption, increase the magnetic field strength, and improve the magnetic separation effect compared to traditional magnetic separation using permanent magnets and electromagnets. In this paper, an open gradient superconducting magnetic separation magnet conduction-cooled by a two-stage GM cryocooler was designed and developed. The open gradient superconducting magnetic separation magnet comprised four saddle-shaped coils and an optimized iron yoke. The radial magnetic flux density was 1 T at a distance of 20 mm from the surface of the coil at an operating current of 120 A, resulting in a magnetic force density of 3.5*10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">7</sup> N/m <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sup> , with a peak field in the coil of 4.82 T. Additionally, this paper proposed a superconducting coil structure and winding method with an end positioning groove. The design and manufacture of the end former, as well as the magnet structure, was completed. Finally, this paper designed a compact cryostat with a two-stage GM cryocooler.

Omnidirectional Wireless Power Transfer System Using Modified Saddle-Shaped Coil Pair for Implantable Capsule Robots

Omnidirectional Wireless Power Transfer System Using Modified Saddle-Shaped Coil Pair for Implantable Capsule Robots

ENCIRCLING EDDY CURRENT TESTING PROBES FOR NON-DESTRUCTIVE TESTING OF CLOSED LINEARLY EXTENDED OBJECTS

In this article, using the example of multi-strand rope inspection, encircling eddy current testing (ECT) probes for non-destructive testing of closed linearly extended objects, for example, stay cables, ropeways or pipelines, are considered. These ECT probes can be divided into parts in the azimuthal direction, which increases the technological effectiveness of the control. The possibility of dividing the ECT probes into parts is provided by using of saddle-shaped measuring coils, saddle-shaped excitation coils or excitation coils of different radii. In addition, the considered ECT probes allow to increase the signal-to-noise ratio.

Motors Employing REBCO CORC and MgB2 Superconductors for AC Stator Windings

Future all-electric aircraft will employ highly efficient compact and lightweight machines for power generation and propulsion applications. Previous studies have indicated that the most attractive options include synchronous machines employing superconducting excitation and stator windings for achieving high power density and efficiency. The dc excitation winding could be constructed using a variety of superconductors, but the choice for ac stator windings is limited. High conductivity aluminum conductor at cryogenic temperature is a possible option but it is expected to be heavier than a superconducting winding and will require more extensive cooling as the losses within the winding pack will be much larger. A conductor-on-round-core (CORC) cable using REBCO tapes looks like an attractive option as it enables compound bending for constructing saddle coils. Here, we investigate using this cable for the stator winding of a 3 MW, 4500 RPM, 4-pole propulsion motor and compare with an identical motor employing an MgB <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> stator winding. The motor configuration assumes saddle-shaped coils for the stator winding. Each saddle coil constitutes a double pancake. A round conductor capable of bending in three-dimensional is preferred for such coils, making the round CORC cable ideal for this application. The cable employs striated REBCO with striation width as small as 1/3 mm. The ac field in the stator winding region is about 0.7 T at 150 Hz and the cable is operated at 50% of its critical current for limiting ac losses and for providing a safety margin. Individual tapes in the CORC cable experience field perpendicular to its broad face resulting in high ac losses. Comparing the performance of motors employing CORC and MgB <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> cables for the stator, we find that the ac losses in the CORC stator are much larger than the MgB <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> stator. High losses in the CORC stator winding make this option less attractive unless coolant power is freely available, such as in LH <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> -fueled planes. However, this machine with CORC coils is the most compact and lightweight option. Such compact light mass motors could be attractive for LH <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> fueled applications, such as interstate trucks, heavy machinery, locomotive hauling goods trains, ships (especially for podded propellers), etc.

Saddle-Shaped Post-Assembly Magnetization Coil for a 300 kW 2-Pole High-Speed Permanent Magnet Rotor

This paper presents the design and test results of a saddle-shaped post-assembly magnetization coil for a 2-pole high-speed permanent magnet (PM) rotor. The magnetization coil can generate pulsed transverse magnetization fields of magnitude equal to 6 T/10 ms in a bore having a diameter of 85 mm and a length of 280 mm, thus meeting the needs of parallel magnetization of a 300 kW 2-pole high-speed PM rotor. The saddle-coil structure improves the coupling between the coil and the rotor, and its magnetic energy reduces to 61% compared to the existing triple-coil structure. The influence of eddy current on the magnitude and direction of the magnetization field is analyzed and the pulse-width and coil supporting structure are optimized. The energy storage of capacitor bank pulse power supply is reduced to 230 kJ, which is 50% of the triple-coil structure's storage. The coil is fabricated and tested, and it is shown that it can successfully magnetize a 300 kW 2-pole high-speed PM rotor.

Fully 3-D Numerical Investigation of Phenomena Occurring in Marine Magnetohydrodynamic Thrusters

A magnetohydrodynamic (MHD) thruster is a type of electric motor which does not have mechanical moving parts and directly converts electrical energy into mechanical energy. In this paper, a multiphysics numerical simulation has been performed to investigate the phenomena occurred in the channel of marine MHD thrusters. In this simulation, all electric, magnetic, and fluid flow fields have been considered 3-D. For this purpose, a marine MHD thruster model with saddle-shaped coils is selected, and its dimensions are determined. Then, this thruster is simulated numerically, and its electromagnetic and fluid flow parameters are studied. In this simulation, the effects of seawater electrolysis and end loss are taken into account. An experimental setup is established to validate the results obtained from the numerical simulation. The results reveal that the nonuniformities of the electric and magnetic fields along the channel have a great impact on the performance of the thruster. Unlike the results obtained in the previous studies, it is shown that the velocity near the electrodes is higher than that near the sidewalls arisen from the higher electromagnetic force close to the electrodes.

Design and Test Results of Superconducting Magnet for Heavy-Ion Rotating Gantry

Heavy-ion radiotherapy has a high curative effect in cancer treatment and also can reduce the burden on patients. These advantages have been generally recognized. Furthermore, a rotating gantry can irradiate a tumor with ions from any direction without changing the position of the patient. This can reduce the physical dose on normal cells, and is thus commonly used in proton radiotherapy. However, because of the high magnetic rigidity of carbon ions, the weight of the rotating gantry for heavy-ion therapy is about three-times heavier than those used for proton cancer therapy, according to our estimation. To overcome this issue, we developed a small and lightweight rotating gantry in collaboration with the National Institute of Radiological Sciences (NIRS). The compact rotating gantry was composed of ten low-temperature superconducting (LTS) magnets that were designed from the viewpoint of beam optics. These LTS magnets have a surface-winding coil-structure and provide both dipole and quadrupole fields. The maximum dipole and quadrupole magnetic field of the magnets were 2.88 T and 9.3 T/m, respectively. The rotating gantry was installed at NIRS, and beam commissioning is in progress to achieve the required beam quality. In the three years since 2013, in a project supported by the Ministry of Economy, Trade and Industry (METI) and the Japan Agency for Medical Research and Development (AMED), we have been developing high-temperature superconducting (HTS) magnets with the aim of a further size reduction of the rotating gantry. To develop fundamental technologies for designing and fabricating HTS magnets, a model magnet was manufactured. The model magnet was composed of 24 saddle-shaped HTS coils and generated a magnetic field of 1.2 T. In the presentation, recent progress in this research will be reported.

Coil End Parts Development Using BEND and Design for MQXF by LARP

End parts are critical components for saddle-shaped coils. They have a structural function where the cables are deformed in order to cross over the magnet aperture. Based on the previous design of the US LARP program for 90-mm aperture quadrupoles (TQ/LQ) and 120 mm aperture quadrupoles (HQ/LHQ) using BEND, the coil ends of the low-β quadruples (MQXF) for the HiLumi LHC upgrade were developed. This paper shows the design of the MQXF coil ends, the analysis of the coil ends during the coil fabrication, the autopsy analysis of the coil ends, and the feedback to BEND parameters.

Multilayered receive coil produced using a non-planar photofabrication process for an intraluminal magnetic resonance imaging

An intraluminal probe coil is a promising signal detecting technique in magnetic resonance imaging (MRI) for small pathological lesions: it may allow acquisition of relatively high resolution images while maintaining similar signal-to-noise ratio (SNR) compared with external coils. In the present work, multilayered, saddle-shaped intraluminal coils with outer diameters of approximately 2mm were fabricated using a newly developed non-planar photofabrication technique. Single-, double- and quadruple-layered coils suitable for side-view scanning were prototyped and evaluated in terms of spatial resolution and SNR at 1.5T. The coils generated intraluminal MR images with sufficient SNR and spatial resolution.

Ingenious Method for Measuring the Non-Orthogonal Angle of the Saddle-Shaped Coils of an SERF Atomic Magnetometer System

The spin exchange relaxation free (SERF) atomic magnetometer has been a research hotspot due to its ultra-high sensitivity. The SERF atomic magnetometer's sensitivity is subject to the accuracy of its compensating magnetic field and the calibration signal. These two processes need a tri-axial coil system to generate the required magnetic fields, which are directly affected by the non-orthogonality of the tri-axial coil system, especially the non-orthogonality between the x- and y-axes coils. In order to solve this problem, an ingenious and effective method for measuring the non-orthogonal angle between the x- and y-axes in a magnetic coil system has been demonstrated in this paper for the first time. This measurement method was only based on the dynamics of the SERF atomic magnetometer and did not need any additional calibration equipment. A large dc magnetic field B <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">y</sub> was applied to the y-axis, such that the magnetic field B <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">yx</sub> projected from B <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">y</sub> on to the x-axis could be measured. By then solving the relevant trigonometric function, we could obtain the non-orthogonal angle. Using this method, we experimentally obtained the non-orthogonal angle of about 84.08° between the x- and y-axes saddle-shaped coils, with a variance of about 0.14°. Finally, the correctness of this method for calculating the non-orthogonal angle was analyzed.

Prompt quality monitoring of InSe and GaSe semiconductor crystals by the nuclear quadrupole resonance technique

To determine the quality of layer-structured semiconductor single crystals, the nuclear quadrupole resonance technique with successive scanning of the entire sample volume and assessment of the structural quality on the basis of the observed spectra is used. The proposed method is appropriate in the case of InSe, GaSe and GaAs ingots grown in evacuated cells by the Bridgman technique and can be used repeatedly in subsequent technological procedures with no operator access to the material. To provide scanning within a limited region of the sample and to ensure efficient interaction of the high-frequency field with the crystal, excitation and detection of the nuclear-spin-induction signal is implemented by the saddle-shaped transceiver coil of the nuclear quadrupole resonance spectrometer.

Influence of Manufacturing Accuracy on Magnetic Field Distribution in Magnet for HTS Rotating Gantry

Because of its high curative effects and low burden on patients, carbon ion cancer therapy is becoming more widely used. The accelerated carbon ions are delivered to patients via electromagnets on a rotating gantry. One advantage of a rotating gantry is that a tumor can be irradiated with carbon ions from any direction without changing the posture of the patient. On the other hand, because of the high magnetic rigidity of carbon ions, rotating gantries for carbon cancer therapy are about three times heavier than those for proton cancer therapy, according to our estimation. Use of high-temperature superconducting (HTS) magnets has been considered for reducing the size of the rotating gantry for carbon cancer therapy. For accurate irradiation, these HTS magnets must generate high-uniformity magnetic fields, and the shape of the HTS coils was designed by 3-D analysis to generate uniform magnetic fields. In our design, saddle-shaped HTS coils were used since they can efficiently generate a magnetic field. The conductor positions and the coil end shape were optimized to generate a uniform magnetic field. On the other hand, it was difficult to maintain the HTS conductor in the designed saddle shape because it has a tapelike shape and anisotropic flexibility in bending. In this paper, the winding accuracy of the fabricated HTS saddle-shaped coil was measured, and the influence of the measurement result on the magnetic field distribution was evaluated.

Decay of Shielding Current in Stacked REBCO Superconducting Tapes

We are developing superconducting magnets for MRI with $\mbox{Re}_{1}\mbox{Ba}_{2}\mbox{Cu}_{3}\mbox{O}_{7-\delta}$ (Re: rare earth, Y, Gd, Eu, REBCO) tapes. Superconducting magnets for MRI need the uniformity of the produced magnetic field in time and space. The disturbance is mainly caused by the induced shielding current in the wound superconducting tapes, which corresponds to the magnetization of the REBCO superconducting tapes. We have made a test coil with REBCO tapes and evaluated the influence of the shielding current on the produced magnetic field. In this paper, applying external magnetic field perpendicular to the EuBCO superconducting tape face, we investigated the magnetization and its relaxation properties of the tapes at 20–40 K using a saddle-shaped pickup coil. Increasing an applied magnetic field and interrupting the field sweep temporarily at 0, 0.5, 1, 1.5, 2, and 2.5 T, we observed the variation of the magnetization for each step of magnetic field. The magnetization decayed at a speed of a few to tens of percent per minute. It was faster beyond expectation. The relaxation rate of the magnetization depended on magnetic field, temperature, and the number of stacked tapes. It became faster with increasing temperature and magnetic field and with decreasing number of stacked tapes.

Thermal Stability of Conduction-Cooled HTS Magnets for Rotating Gantry

Carbon ion cancer therapy is becoming more widespread due to its high curative effects and low burden on patients. In particle cancer therapy, it is desirable that the treatment beam irradiates the tumor from different directions in order to reduce the dose on normal cells. A rotating gantry is a suitable apparatus for meeting this requirement. Since the irradiation device orbits a patient inside the gantry, the beam can irradiate the tumor from any direction without changing the posture of the patient. Rotating gantries are already commonly used for proton cancer therapy. On the other hand, those designed for carbon ion cancer therapy have not yet been adopted because they are too large and heavy for installation in general hospitals. An R&D project to reduce the size of a rotating gantry for carbon ion cancer therapy by applying high-temperature superconducting (HTS) magnets is now in progress. It is difficult to use a coolant for the magnets mounted on the rotating gantry because they are rotating. Therefore, conduction cooling should be employed. On the other hand, the magnetic field generated by the magnets of the rotating gantry should be changed depending on the energy of the carbon ion beam in raster-scanning irradiation, and there is some possibility that the carbon ion beam will collide with the coils. This causes anomalous thermal inputs, such as those due to ac loss and beam loss, resulting in the problem of poor thermal stability of the conduction-cooled HTS coils heated by such thermal inputs. Therefore, it is important to estimate the thermal stability of the conduction-cooled HTS coils correctly. In this paper, a saddle-shaped HTS coil was designed, and the thermal runaway current of the HTS coil was numerically simulated.

Development of Saddle-Shaped Coils for Accelerator Magnets Wound With YBCO-Coated Conductors

With the advances made in accelerator technologies, particle accelerators are being employed in a wide range of fields such as physics, biology, and medical treatment. However, the diameters of the main rings in most accelerators are large; for example, even the smallest carbon cancer therapy accelerator has a main ring diameter of approximately 20 m. Since a rotating gantry for a carbon-ion beam is also very large compared with the gantry for a proton beam, widespread adoption of this therapy system has been restricted. In order to promote widespread adoption of carbon cancer therapy accelerators, it is necessary to reduce the bending radius of the carbon-ion beam. One way to achieve this is to use superconducting magnets with higher magnetic fields. High-T c superconducting (HTS) magnets have higher thermal stability and need lower power consumption for cooling than low-T c superconducting (LTS) magnets. Although saddle-shaped coils are suitable for accelerator magnets, an HTS conductor has anisotropic bending flexibility because of its tape shape. To evaluate winding technologies for HTS saddle-shaped coils, a number of coils were fabricated and tested. The test coils were about 400 mm long and 160 mm wide. Each test coil was wound using an approximately 45-m-long 4-mm-wide YBa 2 Cu 3 O x (YBCO)-coated conductor. Some of the coils were excited to measure their voltage-current characteristics in liquid nitrogen. An index value over 20 was obtained throughout an electric field range down to 10 -7 V/m, which indicated that the superconducting properties would not be degraded. To evaluate the quality of the magnetic field distribution and the thermal stability of a conduction-cooled HTS magnet, we fabricated and tested an HTS magnet consisting of eight saddle-shaped coils.

SIMULATION OF MAGNETIC FIELD TOPOLOGY IN A SADDLE-SHAPED COIL OF NUCLEAR QUADRUPOLE RESONANCE SPECTROMETER

A topology of high-frequency field intensity in the work area of a saddle-shaped coil for a nuclear qaudrupole resonance spectrometer was studied. With a view to determine magnetic field topology, a computational domain was created which is a model of a saddle-shaped coil physical structure. Finite element method was used to perform numerical simulation in COMSOL Multiphysics software. According to the results of calculations performed and the field maps obtained, the relative volume of coil work area was determined which makes 28.12% of its full volume. For such a volume the recommended size of samples under study is 12× 18× 10mm3.

Generation of long prolate volumes of uniform magnetic field in cylindrical saddle-shaped coils

We investigate the uniformity of the magnetic flux density (referred to as the field uniformity) within a series of coils designed to provide a prolate volume of field uniformity. Computational modelling of two cylindrical coil systems which have a sinusoidal current density distributed on the surface of the cylinder, shows the extent of prolate field uniformity along the cylindrical axis, with height and width of the magnetic volume limited by the radius of the cylinder. The first coil system consists of a cos θ coil–-a series of saddle-shaped filament loops spaced uniformly with respect to cos θ on the curved cylindrical surface, where θ is the angle between the radius of the cylinder and the horizontal radial axis (assuming a horizontal cylinder). The second coil system, named the ‘ELFcage’ coil, consists of saddle-shaped filament loops spaced uniformly with respect to a fixed Δθ, on the cylindrical surface. The volume of field uniformity is also compared with volumes generated by circular Helmholtz and Barker coil designs. For coil diameters of 2 m, the Helmholtz and Barker coils generate a volume of field uniformity within 1% to 3% of the field at the centre that extends ∼0.8 m and ∼1.4 m respectively along the axis of symmetry. This compares to an extent of 3 m and 6 m for both the cos θ and ELFcage coils wound on a 2 m diameter cylinder (8 m length), for 1% and 3% field uniformity respectively. Importantly, the ELFcage coil shows significantly greater field uniformity along the radial axis compared to the cos θ coil. An array of triaxial magnetometers was used to measure the volume of field uniformity within the cos θ coil system, consisting of two sets of orthogonal cos θ windings to generate radial fields and a solenoid winding to generate an axial field. These measurements confirmed the results obtained from computational modelling. The cos θ coil system is currently in use for calibration of magnetometers and for measuring the magnetic signatures of bulky prolate objects.

Development of Saddle-Shaped Coils Using Coated Conductors for Accelerator Magnets

A project to develop fundamental technologies for accelerator magnets using high-T <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">c</sub> superconductors is currently underway. The primary applications in this project are fixed field alternating gradient (FFAG) accelerators for carbon cancer therapy systems and accelerator-driven subcritical reactors. One of the challenging issues in this study is to accomplish the complicated coil shape required for the accelerator magnets using YBa <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> Cu <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">x</sub> (YBCO) coated conductors. An asymmetric, three-dimensional winding structure has been designed for the main ring of an FFAG accelerator, but the anisotropic bending flexibility of coated conductors is constrained because of their tape-like shape. To demonstrate a suitable winding technology for a three-dimensional coil using coated conductors, a prototype winding machine with a two-axis motion mechanism was constructed. Based on the present design of the FFAG magnet, a saddle-shaped coil wound on a curved surface with a radius of 700 mm was designed. A 100-turn coil was wound by the winding machine using an approximately 90 m length of 3 mm-wide YBCO coated conductor made by the IBAD-MOCVD method. The coil was impregnated with epoxy resin, and the voltage-current ( <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">V</i> - <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">I</i> ) characteristics were evaluated in a liquid nitrogen environment. From the <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">V</i> - <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">I</i> characteristics in an electric field region of 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-9</sup> V/cm, an index value of above 20 was obtained, which means that the superconducting properties were not degraded.