High Temperature Superconducting Bulk Magnet Research Articles

Magnetic separation of nickel-plating waste liquid using a high temperature superconducting bulk magnet

Ni is one of the important metal resources. Because Ni-containing waste liquid is drained after several plating turns in the factories, an effective recycling technique should be developed. A unique magnetic separation technique using high temperature superconducting bulk magnet has succeeded in collecting Ni-sulfate crystals, which were fabricated from the Ni-plating waste liquid. Pulsed-field magnetizing method was employed to activate the bulk magnet up to 2.80 T, which produced a field space of 1.40 T on the surface of the waste channel. Green coarse crystals were attracted from the flowing stream of Ni-saturated liquid containing weakly-magnetic particles of Ni-compounds. The magnetically-collected particles were identified as paramagnetic NiSO4/6H2O crystals, and slight differences in Ni concentration and grain size were observed between the particles attracted and not-attracted to the 1.8 T magnetic pole. In both cases, the large grains were found to consist of a single phase. The compound can be used as a raw material in the Ni-recycle process. This preferential extraction suggests a novel recycling method of Ni resource.

Stability model of bulk HTS field pole of a synchronous rotating machine under load conditions

High-temperature superconducting (HTS) bulks act as magnets with trapped magnetic flux and potentially exhibit high magnetic field performance, superior to that of permanent magnets. In the fourth industrial revolution, HTS magnets could potentially facilitate the development of highly efficient and lightweight motors and generators for propulsion. To evaluate and verify the durability of HTS rotating machines, we developed a radial-gap-type rotating machine whose field-pole modules comprised HTS bulks. We examined the stability of the trapped magnetic flux of the field poles during the machine’s operation. The rotating machine was operated with different loads, and the magnetic field associated with the trapped flux of the HTS bulks was analyzed. The analysis was performed for different loads and revolution speeds, and the long-term operation for a constant load was investigated. The trapped flux of the bulk field poles and the output power were observed to be almost constant for over 360 h, and the HTS bulk magnet’s surface temperature hardly changed below 40 K during the machine’s operation. Furthermore, the magnetic flux decay determined from magnetic flux measurements before and after a load test was less than 1%. An analysis of the magnetic field distribution around the HTS bulk revealed that the transverse magnetic flux flowed through the magnetic guide of the rotor core. These results indicate the potential synchronous machine application of the high trapped magnetic flux of the field-pole modules accumulated by the appropriate positioning the HTS bulks three-dimensionally.

Nonlinear Vibration Behaviors of Side-Placed High-Temperature Superconducting Bulk and Permanent Magnet System

The vibration properties of a side-placed high-temperature superconducting (HTS) bulk and permanent magnet (PM) system have been investigated theoretically and experimentally. In this system, an HTS pendulum (HTSP) is introduced to laterally arrange the HTS bulks beside a PM with a high pinning force. The resonant frequency nearly linearly decreases when increasing both the mass of HTSP and the gap between superconductors and a magnet. The results indicate that the resonant frequency is dependent on HSTP mass and stiffness. This may be helpful for the future application on close-proximity spacecraft operations and maglev system.

Novel magnetizing technique using high temperature superconducting bulk magnets for permanent magnets in interior permanent magnet rotors

A novel magnetizing technique for permanent magnets (PMs) embedded in interior permanent magnet (IPM) motors has been proposed as a safer and more effective process than the conventional processes using copper pulse-coils. In the new process, the high temperature superconducting (HTS) bulk magnet, emitting an intense magnetic field of over 3 T, was employed to activate the rotor and PMs inside. A magnetic pole containing the HTS bulk magnet was scanned on the surface of the IPM rotor, resisting against the extremely strong attractive force between the magnet and rotor. Following experiments in the past, numerical simulation studies have been conducted to evaluate the magnetic field-trapping performances of the PMs. In this study, the numerical analysis of the magnetization behaviours was conducted for the PMs embedded in the rotor of the commercial air-conditioner motor in a hybrid car. The simulation results showed us that the demagnetized Nd-Fe-B plates in the rotor were fully magnetized in the intense static magnetic fields on the magnetic pole containing the HTS bulk magnet. The magnetizing behaviour in this peculiar magnetizing operation was made understandable by estimating the anisotropic easy-direction of the PM plates embedded in the rotor. The novel activation method for PM is characterized as a no-shock and no-heating method, which would promote the degree of freedom in the IPM motor design.

Magnetizing Technique for Permanent Magnets in IPM Motor Rotors Using HTS Bulk Magnet

A unique activation technique for permanent Nd-Fe-B magnets which were embedded in the rotors of interior permanent magnet (IPM) motors has been developed as a magnetizing tool with use of high temperature superconducting (HTS) bulk magnet. The experimental and numerical simulation studies were conducted to evaluate the magnetic field-trapping performances of the rotor of air-conditioner compressor in the hybrid-type automobiles. The sample rotor containing six demagnetized permanent magnet plates were exposed in the intense static magnetic fields above the magnetic pole which contained the bulk magnet generating over 4 T. As a result, the sample magnets were perfectly magnetized in the static magnetic field. The precise simulation on the flux distribution in the rotor clarified that it is important to make the flux direction in the rotor core and the easy magnetization axis of PM identical. We convinced this activation technique should enable us to promote the degrees of freedom of motor designing and its processing.

Formation of uniform magnetic flux distribution for NMR magnets using HTS bulk magnets activated by pulsed-field magnetization

Nuclear magnetic resonance (NMR) magnets generally need an extremely uniform magnetic field in the space where the specimens will be placed. Although high temperature superconducting bulk magnets can obtain an intense magnetic field of more than 3 T, the field distribution is intrinsically characterized to be inhomogeneous, showing steep gradient. Aiming at the practical application of compact and portable NMR magnets, the authors have developed magnet systems capable of generating uniform magnetic fields in a narrow space between face-to-face settled magnetic poles, targeting to obtain a uniform magnetic field between the poles. Here, the authors modified the shape of magnetic field distribution from convex to concave by attaching a ferromagnetic iron plate on one of the pole surfaces, and then settled them face to face with a gap of 70 mm. The uniformity of the magnetic field in the x-y plane was experimentally measured and estimated along various z-axis directions. The best uniformity of 463 ppm at 1.25 T was obtained in the experimental evaluation in the x-y plane of 4 × 4 mm2 at z = 0.5 mm from the iron plate surface. The value of uniformity along the z-direction range was extended from 0.8 mm to a depth of 1.1 mm. These results show that the possible space of NMR signal detection or the available sample size can be enlarged.

Feasible Applications of Bulk HTS Magnets and Magnetic Field-Capturing Characteristics in Their Activation Processes

Feasible applications in the industrial regions for the bulk high-temperature superconducting (HTS) magnets have been investigated in two categories of the strong magnetic field generators and the magnetic levitation devices by active and passive field trapping, respectively. When we adopt the system to the active field generators, magnetization procedures are necessary. The authors have studied the field-capturing abilities of the HTS bulk magnets on two ways of the activation procedure and the material designing. In the former, we clarified the magnetic flux behavior that invades into bulk magnets, and that the invading flux motion is affected by the previously existing flux distribution. Therefore, the magnetic flux can be accumulated with successive magnetic fields applications with descending heat generation in order. In the latter, the selective magnetic field invasion was observed between wide- and narrow-growth sector regions. Since the bulk magnets with steep magnetic field distributions deform their own field distribution shape to be uniform by the shielding effect when the ferromagnetic plate was attached on the magnetic pole, we have succeeded in obtaining the uniform magnetic field of several-hundred parts per million in the space between the magnetic poles.

Effect Laws of Different Factors on Levitation Characteristics of High-Tc Superconducting Maglev System with Numerical Solutions

The interaction between the high-temperature superconducting (HTS) bulk and permanent magnet guideway (PMG) has been a topic among the existing HTS magnetic levitation systems. Up to now, the theories about the electromagnetic and force characteristics have been relatively consummated. Here, using the finite element model by COMSOL Multiphysics 5.3a, we investigated the impact of the intrinsic and external factors on the levitation characteristics of HTS maglev systems, the application laws are concluded. Factors including the critical current density and geometric dimensions of the bulk superconductor, as well as the moving velocity, are discussed. The effects of the multiple back and forth movements are also analyzed. By comparing calculation results of the distributions of the induced current and the levitation force of the bulk superconductor, we can clearly confirm the effect laws of various factors on the electromagnetic characteristics and levitation force. These observations support the physical parameters that are difficult to be tested by experiments. And they also have a significant contribution to the experimental condition selections and optimization of the high-temperature superconducting magnetic levitation.

Development of HTS Bulk NMR Relaxometry With Ring-Shaped Iron

The compact NMR magnets consisted of the stacked high-temperature superconducting (HTS) GdBCO bulk annuli trapped by field cooling (FC) method have been developed. The target values of strength and homogeneity of magnetic field for proposed NMR relaxometry are 1.5 T and 150 ppm/cm3, respectively, at liquid nitrogen temperature. Since last year, we have been developing a hardware and software to detect the NMR signals by ourselves. Therefore, we needed to determine the final structure of HTS bulk magnet to be used in the NMR relaxometry. We can obtain the trapped magnetic field over 1.5 T at 77.4 K experimentally. However, it is still difficult to obtain the magnetic field homogeneity under 150 ppm/cm3 experimentally, due to their different superconducting properties. Therefore, in this study, four types of HTS bulk magnets to determine the final structure of compact NMR relaxometry were designed and their field properties including the degraded HTS bulk were investigated using three-dimensional finite-element method analysis. The field properties of 10-stacked HTS bulk magnets with the ring-shaped irons for field compensation and the degraded HTS bulk were investigated experimentally.

Magnetic Separation Using HTS Bulk Magnet for Cs-Bearing Fe precipitates

A peculiar magnetic separation technique has been examined in order to remove the Cs-bearing Fe precipitates formed of the waste ash from the withdrawn incinerator furnaces in Fukushima. The separation system was constructed in combination with high temperature superconducting bulk magnets which generates the intensive magnetic field over 2 T, which was activated by the pulsed field magnetization process. The separation experiment has been operated with use of the newly-built alternating channel type magnetic separating device, which followed the high-gradient magnetic separation technique. The magnetic stainless steel filters installed in the water channels are magnetized by the applied magnetic fields, and are capable of attracting the precipitates bearing the Fe compound and thin Cs contamination. The experimental results clearly exhibited the positive feasibility of HTS bulk magnets.

Superior homogeneity of trapped magnetic field in superconducting MgB2 bulk magnets

Homogeneity of trapped magnetic field in radial and circumferential directions of high temperature superconducting bulk magnets, MgB2 (Tc ∼38.3 K) and YBa2Cu3Oy (Tc ∼91.5 K), have been measured. In polycrystalline MgB2 bulks, the circularity of trapped magnetic field in a cylindrical disk is over 97% at 20–32.5 K, while that of YBa2Cu3Oy was ∼87% at 77 K. Magnetic field distribution of MgB2 bulk was satisfactorily homogeneous and these measurements suggest MgB2 bulks with highly efficient cryocoolers should be very useful for novel high field permanent magnet applications.

Study on the Magnetic Field Homogeneity of HTS Bulk Magnets Including the Degraded HTS Bulk for Developing the Compact NMR Relaxometry

We have been studying the compact magnet for NMR device that consists of a stacked high-temperature superconducting (HTS) GdBCO bulk annuli trapped by a field cooling method. It was difficult to trap the uniform magnetic field above 4.7 T (200-MHz-class NMR magnet) and field homogeneity under 0.01 ppm/cm 3 at liquid nitrogen temperature (77.4 K) because of the low $Jc$- $B$ characteristics of present HTS bulks. On the other hand, the strength and homogeneity of the magnetic field required for NMR relaxometry device are 1.5 T and 150 ppm/cm 3 , respectively. Therefore, we have been investigating the development of the compact magnet for NMR relaxometry device. In our previous work, we obtained the trapped magnetic field over 1.5 T at 77.4 K using the stacked HTS bulk magnet with 80-mm height, and 150-ppm/cm 3 field homogeneity was obtained using the fabricated field compensation methods. However, the asymmetric problem of the magnetic field uniformity occurs by the different superconducting characteristics of HTS bulks when we produce the compact NMR magnet by stacking a large number of HTS bulks. Therefore, in this study, the field homogeneity of HTS bulk magnet by the arrangement of the degraded HTS bulk was investigated using 3-D FEM analysis. We examined the effects of the stacking position of degraded HTS bulk using various $Jc$- $B$ characteristics.

Waveform control pulse magnetization for HTS bulk magnet

For the past 10 years, we have studied high-temperature superconducting (HTS) bulk magnets for use in electromagnetic rotating machines. If the magnetic field effectively magnetizes the HTS bulk, then the size of the motor and generator can be reduced without a reduction in output. We showed that the melt-textured Gd-Ba-Cu-O HTS bulk effectively traps a high magnetic field using waveform control pulse magnetization (WCPM). WCPM makes it possible to generate any pulsed magnetic field waveform by appropriately changing the duty ratio of the pulse width modulation. By chopping so that the pulsed magnetic field has a period of about 1ms, the WCPM technology enables active control of the rise time and suppresses magnetic flux motion that decreases magnetization efficiency. This method is also useful for any HTS bulk magnet, and the high magnetic flux density is trapped in the HTS bulk by a single pulse magnetic field. We developed a magnetizer that has a feedback system from the penetrated magnetic flux density to realize WCPM. In this research, using only a single pulse magnetic field of WCPM method at 77K, an HTS bulk with a 45mm diameter and 19mm thickness trapped a maximum magnetic field of 1.63T, which is more than 90% of the trapped magnetic flux density by FC magnetization. This result suggests that the pulse magnetizing method can replace the conventional field-cooled method and promote the practical use of HTS magnets for electromagnetic power applications.

Study on the Magnetic Field Homogeneity of Stacked HTS Bulk Magnets Including the Deteriorated HTS Bulk by Crack for Compact NMR Relaxometry

We have been studying the compact magnet for NMR device that consists of a stacked high temperature superconducting (HTS) GdBCO bulk annuli trapped by a field cooling (FC) method. It was difficult to trap the uniform magnetic field above 4.7 T (200 MHz-class NMR magnet) and field homogeneity under 0.01ppm/cm3 at liquid nitrogen temperature (77.4K) because of the low Jc-B characteristics of present HTS bulks. On the other hand, the strength and homogeneity of the magnetic field required for NMR relaxometry device are 1.5 T and 150ppm/cm3 respectively. Therefore, we have been investigating the development of the compact magnet for NMR relaxometry device. In our previous study, we obtained the trapped magnetic field over 1.5 T at 77.4K using the stacked HTS bulk magnet with 80mm height, and 150ppm/cm3 field homogeneity was obtained using the fabricated field compensation methods on inner diameter of 20mm HTS bulk magnet. However, it is expected that the asymmetric problem of the magnetic field uniformity will be occurred by the crack in the HTS bulks with long-term operation. Therefore, in this study, the field homogeneity of HTS bulk magnet by the arrangement of the HTS bulk with crack was investigated using 3-D FEM analysis. We examined the effects of the stacking position of HTS bulk with the crack and the allowable range of degradation of HTS bulk to achieve the target field homogeneity of 150ppm/ cm3.

Magnetization behavior of RE123 bulk magnets bearing twin seed-crystals in pulsed field magnetization processes

Melt-textured Y-Ba-Cu-O high temperature superconducting bulk magnets were fabricated by the cold seeding method with using single or twin-seed crystals composed of Nd-Ba-Cu-O thin films on MgO substrates. The behavior of the magnetic flux penetration into anisotropic-grown bulk magnets thus fabricated was precisely evaluated during and after the pulsed field magnetization operated at 35 K. These seed crystals were put on the top surfaces of the precursors to grow large grains during the melt-processes. Although we know the magnetic flux motion is restricted by the enhanced pinning effect in temperature ranges lower than 77 K, we observed that flux invasion occurred at applied fields of 3.3 T when the twin seeds were used. This is definitely lower than those of 3.7 T when the single-seeds were employed. This means that the magnetic fluxes are capable of invading into twin-seeded bulk magnets more easily than single-seeded ones. The twin seeds form the different grain growth regions, the narrow-GSR (growth sector region) and wide-GSR, according to the different grain growth directions which are parallel and normal to the rows of seed crystals, respectively. The invading flux measurements revealed that the magnetic flux invades the sample from the wide-GSR prior to the narrow-GSR. It suggests that such anisotropic grain growth leads to different distributions of pinning centers, variations of Jc values, and the formation of preferential paths for the invading magnetic fluxes. Using lower applied fields definitely contributed to lowering the heat generation during the PFM process, which, in turn, led to enhanced trapped magnetic fluxes.

A gradient coil design for a high-temperature superconducting bulk magnet using the finite-difference method

The screening current induced in a bulk superconductor presents a critical problem for gradient coil design because it gives rise to undesirable effects on the gradient field: namely, a decrease in the efficiency and a distortion of the field. In this paper, a new coil design method for the bulk magnet is proposed using the finite-difference method (FDM) and the target-field method. The calculation using the FDM was implemented with the boundary conditions of the bulk magnet. Transverse and longitudinal coils were designed and fabricated for a high-temperature superconducting bulk magnet. The calculated results of the efficiency and the nonlinearity distribution of the gradient field agreed well with the measured results.

The Study to Improve the Field Homogeneity of the NMR Relaxometry Magnets Using the Packaged HTS Bulks With Various Iron Rings

The compact magnet for NMR device that consists of a stacked high temperature superconducting (HTS) Gd-Ba-Cu-O bulk annuli was trapped by a held cooling method. However, it was difficult to trap the uniform magnetic held above 4.7 T (200 MHz-class NMR magnet) and held homogeneity under 0.01 ppm/cm3 at liquid nitrogen temperature (77.4 K) because of the low Jc-B characteristics of present HTS bulks. On the other hand, the strength and homogeneity of the magnetic held required for NMR relaxometry device are 1.5 T and 150 ppm/cm 3 respectively. It is easily to generate the trapped magnetic held over 1.5 T at 77.4 K using the stacked HTS bulks, but it is still hard to obtain 150 ppm/cm 3 held homogeneity with the conventional superconducting magnet (SCM) as the magnetizing magnets. Therefore, we have studied the compensation methods to improve the held homogeneity. In this paper, we proposed the packaged HTS bulk magnet consisted of HTS bulks annuli and various iron rings as the held compensation, and investigated it in analysis and experiment.

Preferential Magnetic Flux Invasion and Heat Generation Owing to Macrostructure in HTS Bulk Magnets in Pulse Field Magnetization Processes

In order to clarify the behavior of the magnetic flux that invade into the melt-processed Dy123-based high-temperature superconducting bulk magnet, the motions of magnetic fluxes and the phenomena of heat generation were precisely measured during the pulsed field magnetization processes. In the experiments, we estimated the time evolutional profiles that were measured at two portions in the growth sector region and the growth sector boundary. They are characterized as the areas of lower and higher critical current densities than each other, respectively. The serial pulsed magnetic fields of 5 T were applied to the sample at 30 K, and the data were obtained in turn by the Hall sensor and thermometer that were put at several positions along the radial rows on the growth sector boundary and the growth sector region. The profiles of magnetic flux during the pulsed field application actually proved that the magnetic flux invades the sample through the growth sector regions in shorter time and with stronger magnitude than through the growth sector boundaries. Since the low magnetic field application leads to low heat generation, it is expected to achieve the higher trapped field performances than ever.

Measurement and Calculation Method of the Radial Stiffness of Radial High-Temperature Superconducting Bearings

Stiffness of radial high-temperature superconducting (HTS) bearings is widely researched by experiments (measurement method). These researches include radial stiffness and axial stiffness at different temperatures and rotational speeds, cross stiffness, and so on. The measurement method can obtain the precise value of stiffness, while it takes so much time and cost. Simulation calculation method is suitable to model radial HTS bearings which have different structures, and it is easier to obtain stiffness than the measurement method. The problem is that the calculation precision is sensitive to the parameters in the simulation calculation. The measurement and calculation method of the radial stiffness of radial HTS bearings has the strong points of saving time and cost, and high precision. In this paper, this method is improved. Radial stiffness between HTS bulk and permanent magnet (PM) rotor is analyzed basing on a new mechanical model, and equation for the radial stiffness of radial HTS bearings is deduced. The error of calculation is reduced to 2.86 % according to the measured values. Application of this method for calculating the radial stiffness of radial HTS bearings with different number of HTS stator layers is introduced.

Numerical Study to Obtain the Improved Field Homogeneity and Enlarged Inner Diameter of HTS Bulk Magnet for Compact NMR

We have been studying the compact magnet for NMR device that consists of a stacked high temperature superconducting (HTS) GdBCO bulk annuli. We can generate the trapped magnetic field over 1.5 T at 77.4K and 150ppm/cm3 on inner diameter of 20mm HTS bulks using field compensation methods. However, it is necessary to enlarge the inner diameter of the HTS bulk magnet because the diameter of commercial NMR probe is larger than 20mm. In this paper, we studied an optimal shape of the stacked HTS bulk magnet to obtain the enlarged inner diameter using 3-D FEM based analysis. We was able to enlarge the inner diameter of the HTS bulk magnet from 20mm to 34mm remaining magnetic field strength of 1.5 T and magnetic field homogeneity of 666ppm/cm3 by proposed passive field compensation method.