HTS Bulk Magnet Research Articles

NMR Relaxometry Using Outer Field of Single-Sided HTS Bulk Magnet Activated by Pulsed Field

We have succeeded in getting <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1</sup> H NMR signals at 47.8 MHz (1.12 T) from a single-sided HTS bulk magnet activated by pulse-field magnetization. Diffusion NMR using an inhomogeneous outer field was also demonstrated on the surface. This kind of NMR relaxometry can not get the information of molecular structures, which conventional NMR using a homogeneous magnetic field can acquire. However, the relaxation of nuclear spin magnetization is still observable. A higher magnetic field gradient generated by the small HTS bulk magnet, 67 T/m at a 5 mm distance from the surface, can be effectively used to observe the self-diffusion coefficient of liquids in higher spatial resolution, 44 μm. The easy accessibility to the strong field gradient is one of the unique properties ofcompact HTS bulk magnets. We believe that single-sided (unilateral) diffusion NMR will become the new application of HTS bulk magnets.

Influence of the Shape of Soft-Iron Yoke on Trapped Field Performance of HTS Bulk

We investigate the influence of soft-iron yokes on the magnetizing characteristics of HTS bulk magnet excited by pulsed field magnetization (PFM). By using the yoke, the trapped field could be improved because the bulk was exposed to the magnetic field for a long time due to hysteresis characteristic. In our previous study, a magnetizing test was performed by using the yokes with different size, resulting that the trapped field of a large yoke was higher than that of a small one. In this study, an effect of the shape of yoke on trapped field performance was evaluated quantitatively. A GdBCO bulk 60 mm in diameter and 20 mm thick was magnetized by using the disk-, ring- and cross-shaped yokes. The trapped field of the cross-shaped yoke was the highest, and that of the ring-shaped yoke was the smallest. However, when the total magnetic flux per unit weight of the yoke was compared, its value of the ring-shaped yoke was a little higher than that of the disk-shaped one. These results provided the possibility of reducing the weight of the system while maintaining the high trapped field by decreasing the volume of soft-iron yoke.

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.

Development of RE-Ba-Cu-O Bulk Superconductors, QMG

This paper describes the development of RE-Ba-Cu-O (RE:Y or rare earth elements) bulk superconductors (“bulks”). HTS bulks have a great potential to pioneer a new application field of superconductors. The high-quality HTS bulks developed by Nippon Steel Corporation are called “QMG”, which is a single-grained material of REBa2Cu3Ox (RE123) with RE2BaCuO5 (RE211) inclusions finely dispersed in the superconducting matrix. The name QMG originally comes from the initial process, “Quench and Melt-Growth”. However, no quench step is required in the advanced QMG process, and thus “Q” now means “Quality” instead of “Quench”. The key point of QMG technologies is the simultaneous control of the crystal growth and the micro-structure. Although it is believed to be very difficult to produce large single-grained HTS bulks exceeding 80 mm in diameter, we have succeeded in enlarging QMG up to 150 mm using the RE compositional gradient method. These ultra-large HTS bulks have been used for the superconducting magnetic bearing (SMB) of the flywheel energy storage system in Yamanashi, Japan, contributing to non-contact support of a heavy 4,000 kg rotating flywheel. In addition to SMB, other promising application are HTS bulk magnets for ship propulsion motors, wind or tidal power generators, and desktop cryogen-free NMR/MRI. HTS bulks are also an ideal material for current leads. Different bulk properties are required for different applications. We have therefore customized QMG bulks depending on application requirements: Dy-QMG for current leads, Eu-QMG for NMR/MRI, and Gd-QMG for other HTS bulk applications.

Generation of Uniform Magnetic Field between Face-to-Face HTS Bulk Magnets

Aiming to develop the compact nuclear magnetic resonance devices, the authors have been developing the uniform magnetic fields in the space between the face-to-face magnetic poles which contain HTS bulk magnets. The authors deformed the original convex shape of the magnetic field distribution to concave by attaching a ferromagnetic iron plate of 20 mm and 100 mm in diameter on one of the pole surfaces. The magnetic field distribution precisely measured along x-axis changed from concave to convex with increasing distance from the magnetic pole surface, which suggested the presence of magnetically flat region. From the results of mapping on the field uniformity data, we have succeeded in obtaining the field uniformity under 500ppm in the space of 4 x 4 x 0.8 mm3 when the magnetic poles emitting concave and convex field distributions were settled face-to-face with various gaps 30-70 mm. This performance exceeded the target value of 1,500ppm which is necessary to detect the NMR signals.

Magnetizing Performance Evaluation of HTS Bulk Magnet Using a 12 K Refrigerator With High Cooling Capacity

We study a high magnetic field generation using HTS bulk magnets activated by pulsed-field magnetization with the goal of their industrial application. In our previous study, a single-stage GM-type refrigerator and a two-stage GM-type refrigerator with an air-cooled-type compressor and a Stirling refrigerator were used for cooling an HTS bulk aiming at simplifying the bulk magnet system. Now, we developed a new bulk magnet system using a two-stage GM-type refrigerator with a high cooling capacity of 12 W at 20 K aiming to enhance a trapped field by improving the cooling ability. When a GdBCO bulk 60 mm in diameter and 20 mm thick was cooled from the room temperature to the lowest, the lowest temperature was 13.3 K at the sample stage and 45.5 K at the bulk surface for 3.5 h. When a single pulsed field was applied with varying the amplitude and temperature, the maximum flux densities of 3.59 T on the bulk surface and 2.34 T at the pole surface, and the total magnetic flux of 2.48 mWb were achieved at 20 K.

Collecting Ni-Sulfate Compound from Electroless Plating Waste by Magnetic Separation Technique with Use of HTS Bulk Magnets

The authors have developed a useful technique for extracting the Ni-sulfate compound from the “processed waste/fluid” of the electroless Ni-plating processes. After forming the fine NiHPO3 precipitate from the waste, the coarse NiSO4 crystals were synthesized through the reaction with the concentrated sulfuric acid. In the experiment, the open-gradient magnetic separation was employed to collect the NiSO4 crystals from the muddy mixture composed of these compounds. The experiments were practically conducted with use of the Gd123-based HTS bulk magnets generating up to 3.99 T, which were activated by the field cooling magnetizing method operated at 35 K. Intense magnetic field emitted from the bulk magnet attracted the paramagnetic fluid and coarse NiSO4 crystals on the bottom of the water channel, forming a giant drop of NiSO4-saturated clear fluid and the slurry of nickel sulfate hexahydrate. This preferential collection suggests a feasible recycling process of Ni resource as a raw material in the plating processes.

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.

Numerical study to obtain the improved field homogeneity of HTS bulk magnet with enlarged inner diameter for compact NMR

The strength and homogeneity of the magnetic field required for NMR relaxometry device are 1.5 T and 150 ppm/cm3 respectively. It is relatively easy to generate the trapped magnetic field over 1.5 T at 77.4 K using the stacked HTS bulks, and 150 ppm/cm3 field homogeneity was obtained using the fabricated field compensation methods on HTS bulks magnet with 20 mm inner diameter. However, it is still hard to obtain 150 ppm/cm3 field homogeneity without field compensation methods. In this paper, in order to improve the trapped magnetic field homogeneity, the HTS bulk magnet with enlarged inner diameter was proposed and studied as the functions of size and shape of HTS bulk. The analytical study based on FEM was carried out to optimize the shape of HTS bulk magnet with enlarged inner diameter.

Magnetic flux invasion in REBCO bulk magnets with varying pre-magnetized flux distributions in multiple-PFM processes

The motion of magnetic flux invading into the HTS bulk magnets were experimentally studied in their pulsed field magnetization processes. The authors paid attention to the effects of the shapes of the pre-magnetized trapped flux distributions before the successive field applications by means of varying the M-shaped distribution. We estimated the differences of the magnetic flux motions between the Dy123 and Gd123 systems, which might have different Jc properties of each sample. As for the Dy123 system, the increase of remaining flux in the periphery region of the M-shaped distribution resulted in the decrease of flux-trapping according to the promotion of flux invasion. On the other hand, trapped flux density has been raised to 3.4 T owing to the effective suppression of flux invasion for the Gd123 bulk magnet. The experiments showed that the peak heights and the positions of the formerly trapped M-shaped fluxes precisely affect the heat generation and the trapped field performance.

対向配置した高温超伝導バルク磁石を用いた均一な磁場空間を生成する新たな試み

対向配置した高温超伝導バルク磁石を用いた均一な磁場空間を生成する新たな試み

液体窒素冷却の小型NMR 用高温超伝導バルクマグネットの開発

液体窒素冷却の小型NMR 用高温超伝導バルクマグネットの開発

Magnetic Separation for Recovering Ni Compounds From Plating Waste With Use of HTS Bulk Magnets

A characteristic magnetic separation technique has been developed to recycle the Ni resource from the waste fluid of electroless Ni-plating processes. Since the plating waste still contains high concentration of Ni ions after several cycles of plating processes, the magnetic separation experiments were conducted to collect the precipitates containing Ni compounds. After extracting the fine NiHPO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> precipitate from the waste liquid, we synthesized the NiSO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4</sub> crystals from the NiHPO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> precipitates through the reaction with the concentrated sulfuric acid. The open-gradient magnetic separation was employed to separate the NiSO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4</sub> crystals from the mixed slurry composed of the NiSO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4</sub> and the NiHPO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> due to the difference between their magnetic properties. The experiments were practically conducted with use of the Gd123-based HTS bulk magnets with very steep gradient of magnetic field of over 100 T/m, which were activated to the magnetic fields of 1.53 and 1.95 T by the pulsed field magnetization process operated at 35 K. The ratio of NiSO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4</sub> content in the collected slurry attracted to the magnetic poles reached up to 98%, which suggests that the paramagnetic NiSO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4</sub> crystals are preferentially collected by the magnetic force from the mixed slurry in the strong magnetic field generated by the HTS bulk magnet.

Selective Magnetic Field Invasion Into HTS Bulk Magnets in Pulse Field Magnetizing Processes

The magnetic flux invasion into the Dy123-based HTS bulk magnets were experimentally evaluated during the pulsed field magnetization processes. Since the invasion of the magnetic flux into the sample would be expected to be affected by the J c distribution, we estimated the differences of the magnetic flux motions between the growth sector boundary (GSB) and the growth sector region (GSR) by measuring the changes of magnetic flux density and temperature during the pulsed field application of 5 T at 30 K. The experimental results on the temperature measurement showed that the magnetic flux invades into the sample through the path in the GSR prior to that in the GRB region. Furthermore, the changing rate of magnetic flux gradually changed with the position on the GSR, while they irregularly changed and did not exhibited any tendency on the GSB. This means that the magnetic flux straightly invades the sample from GSR heading for the center portion, while it does not uniformly flow on the GRB. As a result, the heat generation occurs in the GSR area prior to the GSB region. The magnetic flux invasion behavior exhibits selective and nonuniform motion, reflecting the difference of the macrostructure on the GSR and the GSB.

Two-Dimensional Measurement Technique for Dynamic Magnetic Flux Density Distribution on the Surface of HTS Bulk

It is indispensable to the development of the superconductive electromagnetic machinery to measure the magnetic held precisely. In general, the scanning of a Hall probe over the HTS bulk is used for the measurement of the magnetic held. Because the Hall probe works mechanically, we need a long time before the measurement is completed. However, information about dynamic magnetic flux density distribution is not obtained. On the other hand, there is a method where several Hall elements placed on the HTS bulk surface measure the magnetic held. It is difficult to measure variation in the dynamic magnetic held by using a Hall element reacting with a delay, but a Hall element completes the measurement on the order of 1 ms. Instead, information about magnetic flux density distribution on the whole of the HTS bulk surface is not obtained. In this study, we have developed the measurement system of which dynamic magnetic flux density distribution is continuously measured using a Hall element to be placed on an HTS bulk surface in a short time. A new magnetic held sensor with 5 × 5 = 25 Hall elements forming a line at regular intervals can measure a magnetic held on the HTS bulk surface every about 1 ms. The 225 Hall elements require 900 electric wirings. On the other hand, our magnetic sensor needs only 76 wirings. We applied pulsed magnetic held to a two-dimensional magnetic held sensor with 5 × 5 = 25 Hall elements for operation verification. The sensor measured a dynamic variation of the magnetic flux density distribution every 0.5 ms. In future, we will clarify the details of the magnetic flux characteristic trapped to HTS bulk magnet by using the two-dimensional magnetic held sensor.

Study of the separation method of structural isomer using Magneto-Archimedes method

Abstract Organic compounds have a problem that the separation of structural isomer in the preparation process requires high energy consumption. This study proposes a new separation method of structural isomer using Magneto- Archimedes method. Firstly, the levitation height of 1, 6-DDA and 1, 10-DDA was respectively calculated by simulation of the forces acting on the particles under magnetic field, and it was indicated that they could be separated by the difference of levitation height. To confirm the phenomenon experimentally, white powders of 1, 6-DDA and 1, 10-DDA were formed into pellets, and were soaked in manganese chloride solution. Then the solution was put on the center of the cryostat of HTS bulk magnet (maximum magnetic flux density is 3T). As a result, it was confirmed that the separation of structural isomer by difference of levitation height could be possible. Keywords : Magnetic Separation, Magneto-Archimedes method, Recycle * Corresponding author: nishijima@see.eng.osaka-u.ac.jp

Uniform Magnetic Field Between Face-to-Face HTS Bulk Magnets Combining Concave and Convex Magnetic Field Distributions

The authors have been attempting to obtain the uniform magnetic field distribution in the space between the face-to-face HTS bulk magnets. The magnetic poles containing the HTS bulk magnets are usually characterized as non-uniform magnetic field distribution. Since the distributions show the conical or convex shapes, it is difficult to obtain the uniform magnetic field spaces even when the magnetic poles would be placed face-to-face. The authors have modified the shape of the distribution of one-side magnetic pole by attaching an iron plate on the surface, and formed the concave magnetic field distribution on the pole surface. The steep concave or convex distributions at each pole surface change to be flat with increasing distance from the pole surface. After the experimental result recording the best uniformity of 358ppm by combining the concave and convex field distributions face-to-face, we attempted to simulate the feasible performance in this configuration. In the numerical simulation, the concave field distribution modified by attaching an imaginary spiral coil on the pole surface was coupled with the original convex field. We succeeded in obtaining the best uniformity of 30ppm at 1.1 T in 4 x 4 mm2x-y plane at 7mm distant from the pole surface in the gap of 30mm. This result suggests that the concave and convex magnetic field distributions compensate the field uniformity with each other with keeping the magnetic field strength in the gap, and also suggests the novel compact NMR/MRI devices in the future.

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.

Study on the Shape Optimization of the HTS Bulk Magnets With Active Compensation for Compact NMR Relaxometry Magnets

Compact NMR magnets consisted of the stacked HTS bulk annuli trapped by a field cooling (FC) method have been suggested and developed. The strength and homogeneity of the magnetic field required for the NMR relaxometry device are 1.5 T and 150 ppm/cm 3 respectively, and 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/cm 3 field homogeneity with the conventional superconducting magnet (SCM) as the magnetizing magnets. In this paper, 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 10 mm gap length in the center region of HTS bulk magnet (we call it “split coil-shaped HTS bulks”) were proposed and studied as the functions of size and shape of HTS bulk. It was studied using 3D FEM based electromagnetic analysis. The improved field homogeneity was obtained by using hybrid models consisted with the HTS bulk and attached small size HTS coil.

A Numerical Proposal of an After Heating Method for Pulse Field Magnetization for HTS Bulk Magnets

A Numerical Proposal of an After Heating Method for Pulse Field Magnetization for HTS Bulk Magnets