HTS Bulk Magnet Research Articles

Development of Magnetic Field Control System Using HTS Bulk for ON/OFF Field Switching and Magnetic Field Amplification

High magnetic fields are used in many branches of modern medicine. So, the techniques for magnetic field concentration are very important, and the novel electromagnets and trapped HTS bulk magnets have been fabricated and used in the cell culture and the bulk magnetic drug delivery system. In general, although superconducting magnet can generate high magnetic fields, on/off magnetic switching is impossible because of its large inductance. Therefore, not only the generating of magnetic field but also controlling of magnetic field including on/off switching are very important issues. So, we have been studied the control methods of magnetic field using HTS bulks. In this study, the magnetic field control system consisted of the various shaped HTS bulks and magnetic sources were proposed to achieve the on/off field control and field amplification. The shape of HTS bulk to develop the magnetic control system was optimized by FEM based on analysis, and the abilities of its field switching and amplification were confirmed by experiments. We found that the HTS bulk with slit did control the applied magnetic field, and amplified magnetic fields were obtained at slit parts of HTS bulks.

Attempt to Generate a Strong and Uniform Magnetic Field by Face-to-face HTS Bulk Elements in a Magnet System

A unique experimental attempt aiming to obtain a uniform magnetic field space as required for NMR has been carried out with use of HTS bulk magnets. The magnetic poles were activated as 1.8 T (North) and 1.4 T (South) at 30K by applyinga pulsed magnetic field up to 7 T, and positioned face-to-face with gaps less than 70mm. The uniformity of the magnetic field required for detecting the NMR signals isless than 1,500ppm at more than 0.3 T in the cross sectional plane of 2 x 2 mm2. After thepreliminary trials whichrevealed auniformity of 5,421ppm at 0.44 T in a70mm gap, we attached a ferromagnetic iron plate to a magnetic pole surface to change the magnetic field distribution to be concave. The best uniformity of 358ppm at 1.11 T was obtained at 9mm distance from the iron plate surface in a gap of 30mm. It is stated that the concave magnetic field distribution was compensated by the counter conical-shape field, resulting in the uniform field plane.

Study on the Remagnetization Process to Improve the Field Homogeneity of the Stacked HTS Bulk Magnets

The compact NMR magnets consisting of stacked HTS bulk annuli trapped by a field cooling (FC) method have been developed. However, it is difficult to trap a uniform magnetic field above 4.7 T (200 MHz-class NMR magnet) and field homogeneity under 0.01 ppm/cm3 at liquid nitrogen temperature (77.4 K) because of the low \mmb Jc-\mmb B characteristics of present HTS bulk magnets. On the other hand, the strength and homogeneity of the magnetic field required for the NMR relaxometry device are 1.5 T and 150 ppm/cm3 respectively; these values are much lower than the conventional NMR device. It is relatively easy to generate a magnetic field over 1.5 T at 77.4 K using the stacked HTS bulk annuli, but it is still hard to obtain 150 ppm/cm3 field homogeneity with the conventional superconducting magnet (SCM) as the magnetizing magnets. In this paper, we proposed that the homogeneity had been improved by utilizing the remagnetization process.

Strong Magnetic Field Generator Containing HTS Bulk Magnets and Compact Refrigerators

The magnetic field distributions of an HTS bulk magnet system were precisely measured between the face-to-face 3.4-T magnetic poles. After the activation by 5-T field cooling magnetization, the magnetic flux density has reached the value of 2.26 T at the center of the 34-mm gap. The sum of the local magnetic fields generated from each magnetic pole coincides with the local field strength in the gap. We estimated the homogeneity of the magnetic flux densities of Bz and By, which were measured at various positions along z and y-axes in the center portion of the 60-mm gap. Since the magnetic flux density becomes smooth with increasing distance, we obtained the smallest distribution range of 123 ppm of Bz = 1.62 T at the center of the gap as for Bz. On the other, as for By, the smallest distribution range of 1125 ppm of Bz = 1.20 T was obtained at z = 1.7 mm distant from the center point. Since there must exist a certain plane which has no vector components along the radius direction at the center of the gap, the closer the z-positions come to the null point, the more homogeneous the field distribution becomes.

Numerical Study on Split Coil-shaped HTS Bulks to Improve the Field Homogeneity for Compact NMR Relaxometry Magnets

We have been developing a new compact NMR magnet using stacked HTS bulks. In this pa er, in order to improve the trapped magnetic field homogeneity and to obtain the enlarged sample space of HTS bulk magnet for compact NMR relaxometry, the HTS bulk magnet with 10mm gap length in the center region of HTS bulk magnet (we call it “split coil-shaped THS bulks”) were proposed and studied as the functions of size and shape of HTS bulk using 3D FEM based electromagnetic analysis. The improved field homogeneity was obtained using notch coil shaped HTS bulk configuration and the field compensation by attached the coil instated of the bulks.

The Study to Improve the Field Homogeneity of the HTS Bulk Magnets for NMR Relaxometry Device by Passive Compensation Methods

In this paper, the compensation method to obtain the high field homogeneity (150ppm/cm3) of compact NMR magnet was studied analytically. In order to improve the trapped magnetic field homogeneity of HTS bulk magnet, we used the packaged HTS bulk magnet consisted of HTS bulks annuli and 3 iron rings for field compensation. We could confirm that the target homogeneity of trapped magnetic field of HTS bulk magnet was achieved by the proposed passive compensation method.

Fundamental study of phosphor separation by controlling magnetic force

The phosphor wastes consist of phosphors with different emission colors, green (LAP), red (YOX), blue (BAM) and white (HP). It is required to recover and reuse the rare earth phosphors with high market value. In this study, we tried to separate the phosphor using the magnetic separation by HTS bulk magnet utilizing the differences of magnetic susceptibility by the type of phosphors. We succeeded in the successive separation of HP with low market value from YOX and BAM including the rare earth using the magnetic Archimedes method. In this method, vertical and radial components of the magnetic force were used.

Study on magnetic gene transfer using HTS bulk magnet

This study aimed to realize local and high-efficient gene expression by suppressing the diffusion of ferromagnetic DNA carriers in a strong magnetic field generated by HTS bulk magnet. DNA–magnetite complexes were prepared as ferromagnetic DNA carrier and the magnetic gene transfer using the DNA carriers was examined. From the results of the simulation and the model experiment, it was shown that the particle diffusion was suppressed within 10mm in diameter by the magnetic field at 20mm above the HTS bulk magnet. The results of in vivo experiments showed that the amount of gene expression was significantly increased by magnetic field.

Flux-invading behaviors and temperature changes in Dy123 bulk magnet in iterative pulse field magnetization process

The flux invasion behaviors into the Dy123 based on HTS bulk magnet were precisely measured during the iterative pulsed field magnetizations operated at 31K. The values of magnetic flux densities were measured at various positions on the bulk magnet sample during and after six successive applications of a peak applied field of 5T. The temperature changes were measured on the sample surface to compare them to the magnetic flux motions in the same manner. The invading flux were apparently repelled by the remaining trapped flux due to the former field application, and the domain where the magnetic flux reached was pushed back outward the sample with increasing the pulse number. The heat generation decreased with the iteration of field applications as well as the magnetic flux invasion expressing the same behavior, and saturated by the sixth field application. The time evolution of temperature measured at various positions on the sample surface showed that the heat generation occurs at the periphery of the sample and propagates toward the center of the sample.

Collection of Ni-bearing material from electroless plating waste by magnetic separation with HTS bulk magnet

The magnetic separation experiment to collect the Ni compounds from the waste liquid of electroless plating processes was conducted in the open-gradient magnetic separation process with the high temperature superconducting bulk magnet system. The magnetic pole containing Gd-based bulk superconductors was activated to 3.45T at 35K in the static magnetic field of 5T with use of a superconducting solenoid magnet. The coarse Ni-sulfate crystals were formed by adding the concentrated sulfuric acid to the Ni-phosphite precipitates which yielded from the plating waste liquid by controlling the temperature and the pH value. The open-gradient magnetic separation technique was employed to separate the Ni-sulfate crystals from the mixture of the Ni-sulfate and Ni-phosphite compounds by the difference between their magnetic properties. And we succeeded in collecting Ni-sulfate crystals preferentially to the Ni-phosphite by attracting them to the magnetic pole soon after the Ni-sulfate crystals began to grow.

Magnetic and Thermal Properties of HTS Bulk Magnet in the Pulsed-Field Magnetizing Process

In order to enhance the field-trapping ability of high Tc superconducting melt-textured bulk materials which act as quasi-permanent magnets when they capture the external magnetic fields, it is important to enhance the mechanical toughness of the materials to stand the stress induced by the magnetic repulsive force and thermal expansion. We adopted a dense Dy123-based bulk material with reduced void concentration in the experiment. Since the heat generations due to the flux motions in the samples results in the degradation of Jc, the time evolutions of the trapped magnetic fields and the temperature rises during and after the pulsed-field magnetizing processes were precisely measured at the same time to evaluate the penetrating flux motions and the heat generations in the sample. A single and couple of the magnetic pulsed fields with various intensities were successively applied to the sample at 30 K. The single magnetic field application exhibited a peak effect in the trapped-field behavior and tended to decline due to the heat generation. In the iterative pulsed-field application, the behaviors of the trapped fields and the temperature changes were found to be inverse between the first and the second pulsed-field applications. This implies that the flux penetration behavior into the sample magnet at the second field application is strongly restricted by the presence of former trapped fields which were formed by the first field applications.

Field trapping property of HTS bulk magnet with reduced voids in pulsed field magnetizing process

The field trapping ability of melt-textured bulk superconductors is usually restricted by the mechanical properties because of the magnetic stress induced in the samples during the activation processes which give them intense magnetic fields of several T Therefore it is of crucial importance to enhance the toughness of the materials by means of reinforcing techniques. In this experiment, we adopted a dense Dy-based HTS bulk sample fabricated by means of controlling the concentration of voids inside during the heat treatment. A single magnetic pulse fields up to 7.66 T have been applied in the temperature range down to 30.6 K with use of GM refrigerator and the profiles of pulsed fields and the resultant trapped fields are discussed with respect to their performances. It was found that the trapped field grows as elongating rise time of the pulsed field and lowering initial temperature. The densely fabricated Dy123 sample was activated up to 1.98 T at 31 K in the same manner with no substantial difference from the porous Gd123 samples when the magnetic pulse field of 7.66 T was applied. The temperature rises up to 20 K are not substancial in comparison to those of the Gd123 compounds which exhibit the temperature rises more than 30 K at 40 K by applying 4.64 T This is attributed to the fact that the Jc value of the dense Dy123 are inferior to that of Gd123, which reflectes the field trapping ability.

Magnetic Field Distribution of Permanent Magnet Magnetized by Static Magnetic Field Generated by HTS Bulk Magnet

Demagnetized rare earth magnets (Nd-Fe-B) can be fully magnetized by scanning them in the intense static fields over 3 T of a HTS bulk magnet which was cooled to the temperature range lower than 77K with use of cryo-coolers and activated by the field of 5 T. We precisely examined the magnetic field distributions of magnetized permanent magnets. The magnetic poles were ` in the narrow space on the surface of the permanent magnet with varying gap distances between the tracks of the HTS magnetic pole. Steep magnetic transitions between N and S were observed in the magnetic field distribution maps after the HTS magnetic poles were alternatively scanned for several times. The magnetizing method has been proposed for designing novel electromagnetic devices including magnetically excellent rare earth magnets which require intense magnetic fields over 3 T.

A Superconducting Magnetization System With Hybrid Superconducting Wire for the Study and Application of Superconductivity

For the study of high-temperature superconductors and for the application of superconductivity, a superconducting high-field magnetization system with a hybrid superconducting coil was designed. This coil is composed of superconducting wires of three kinds-HTS YBCO 2G-wire, high-field and low-field NbTi wires. Three principal purposes of building this system are to inspect the characteristics of disk-shape bulk YBCO, to develop a HTS-bulk undulator, and to magnetize a portable HTS-bulk high-field magnet for application to a resonant X-ray scattering experiment. With four steps of temperature decrease, a two-stage GM-type cryocooler and liquid nitrogen provide cooling for the magnetization system. The hybrid superconducting coil, two cryogenic systems for the magnetization system and the portable HTS-bulk magnet, and the control and monitor systems that were designed are discussed.

Magnetic precipitate separation for Ni plating waste liquid using HTS bulk magnets

The magnetic separation experiment for recycling the nickel-bearing precipitates in the waste liquid from the electroless plating processes has been practically conducted under the high gradient magnetic separation technique with use of the face-to-face HTS bulk magnet system. A couple of facing magnetic poles containing Sm123 bulk superconductors were activated through the pulsed field magnetization process to 1.86T at 38K and 2.00T at 37K, respectively. The weakly magnetized metallic precipitates of Ni crystals and Ni–P compounds deposited from the waste solution after heating it and pH controlling. The high gradient magnetic separation technique was employed with the separation channels filled with the stainless steel balls with dimension of 1 and 3mm in diameter, which periodically moved between and out of the facing magnetic poles. The Ni-bearing precipitates were effectively attracted to the magnetized ferromagnetic balls. We have succeeded in obtaining the separation ratios over 90% under the flow rates less than 1.35L/min.

Performance Analysis of an HTS Magnetic Suspension and Propulsion System With a Double-Sided HTS Linear Synchronous Motor

A novel HTS magnetic suspension and propulsion system driven by a double-sided HTS linear synchronous motor (HTSLSM) has been developed, which is suspended by an HTS magnetic suspension subsystem located on the bottom of the HTSLSM secondary mover. The structural design of the suspension and propulsion system is introduced, and then the magnetization characteristics of the HTS bulk magnets for the HTSLSM are studied and compared by different magnetization methods. The finite-element analysis (FEA) model of the HTSLSM is built up by using an equivalent model of the HTS bulk magnet, and the thrust characteristics of the HTSLSM are also simulated based on the FEA model, and verified by measurements on the prototype. Furthermore, the suspension performance of the HTS magnetic suspension subsystem has also been analyzed by a numerical method based on an equivalent current sheet model of the permanent-magnet guideway. The results show that the HTS magnetic suspension and propulsion system has applicable thrust and suspension performance, and can be applied to the practical applications such as a maglev.

Magnetizing technique for permanent magnets by intense static fields generated by HTS bulk magnets: Numerical Analysis

Abstract A demagnetized Nd-Fe-B permanent magnet was scanned in the strong magnetic field space just above the magnetic pole containing a HTS bulk magnet which generates the magnetic field 3.4 T. The magnet sample was subsequently found to be fully magnetized in the open space of the static magnetic fields. The finite element method was carried out for the static field magnetization of a permanent magnet using a HTS bulk magnet. Previously, our research group experimentally demonstrated the possibility of full magnetization of rare earth permanent magnets with high-performance magnetic properties with use of the static field of HTS bulk magnets. In the present study, however, we succeeded for the first time in visualizing the behavior of the magnetizing field of the bulk magnet during the magnetization process and the shape of the magnetic field inside the body being magnetized. By applying this kind of numerical analysis to the magnetization for planned motor rotors which incorporate rare-earth permanent magnets, we hope to study the fully magnetized regions for the new magnetizing method using bulk magnets and to give motor designing a high degree of freedom.

高温超伝導バルク磁石を用いた埋込構造永久磁石同期機の永久磁石の着磁実験及び数値解析

高温超伝導バルク磁石を用いた埋込構造永久磁石同期機の永久磁石の着磁実験及び数値解析

Bulk Superconductors in Mobile Application

Abstract We investigate and review concepts of multi – seeded REBCO bulk superconductors in mobile application. ATZ's compact HTS bulk magnets can trap routinely 1 T@77 K. Except of magnetization, flux creep and hysteresis, industrial – like properties as compactness, power density, and robustness are of major device interest if mobility and light-weight construction is in focus. For mobile application in levitated trains or demonstrator magnets we examine the performance of on-board cryogenics either by LN2 or cryo-cooler application. The mechanical, electric and thermodynamical requirements of compact vacuum cryostats for Maglev train operation were studied systematically. More than 30 units are manufactured and tested. The attractive load to weight ratio is more than 10 and favours group module device constructions up to 5 t load on permanent magnet (PM) track. A transportable and compact YBCO bulk magnet cooled with in-situ 4 Watt Stirling cryo-cooler for 50 – 80 K operation is investigated. Low cooling power and effective HTS cold mass drives the system construction to a minimum – thermal loss and light-weight design.

Magnetizing of permanent magnets using HTS bulk magnets

A demagnetized Nd–Fe–B permanent magnet was scanned just above the magnetic pole which contains the HTS bulk magnet generating a magnetic field of 3.27 T. The magnet sample was subsequently found to be fully magnetized in the open space of the static magnetic fields. We examined the magnetic field distributions when the magnetic poles were scanned twice to activate the magnet plate inversely with various overlap distances between the tracks of the bulk magnet. The magnetic field of the “rewritten” magnet reached the values of the magnetically saturated region of the material, showing steep gradients at the border of each magnetic pole. As a replacement for conventional pulse field magnetizing methods, this technique is proposed to expand the degree of freedom in the design of electromagnetic devices, and is proposed as a novel practical method for magnetizing rare-earth magnets, which have excellent magnetic performance and require intense fields of more than 3 T to be activated.