Bulk Magnet System Research Articles

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.

Magnetizing characteristic evaluation of REBCO bulk in PFM using different yokes

A REBCO bulk magnet is able to generate a several-tesla-class magnetic field by a compact system with low power consumption. Pulsed field magnetization (PFM), which is one of major magnetization method, has the advantage that the bulk is activated using a conventional equipment in a few seconds, and, therefore, it is suitable for practical use. However, a trapped field is lower than the maximum performance of material. To increase the field, improvement of magnetization method and modification of exciting equipment are considered. We aim to improve the trapped field by changing the exciting system simply and inexpensively. In the bulk magnet system, soft-iron yokes are generally used to extend the pulse width. This paper evaluated magnetizing characteristic quantitatively. A single pulsed field was applied to a new GdBCO bulk using ϕ64-mm and ϕ80-mm soft-iron yokes. The pulse width of ϕ80-mm yoke was about 35% longer than that of ϕ64-mm yoke. When comparing the trapped flux density and total magnetic flux, these values of ϕ80-mm yoke were higher than those of ϕ64-mm yoke. Also, the temperature rise of ϕ80-mm yoke was decreased by approximately 5% as compared with ϕ64-mm yoke, implying that the same effect as the long-pulse method was achieved.

Simulation study for magnetic levitation in pure water exploiting the ultra-high magnetic field gradient product of a hybrid trapped field magnet lens (HTFML)

A hybrid trapped field magnet lens (HTFML) is a promising device that is able to concentrate a magnetic field higher than the applied field continuously, even after removing an external field, which was conceptually proposed by the authors in 2018. In this study, we propose a new additional advantage of the HTFML, which could be applicable for magnetic levitation and separation. The HTFML device consisting of a GdBaCuO bulk cylinder and a GdBaCuO magnetic lens, after the magnetization process from an applied field, Bapp = 10 T, can generate a maximum trapped field, Bc = 11.4 T, as well as an ultra-high magnetic field gradient product, Bz⋅dBz/dz, over ±3000 T2/m at Ts = 20 K, which is higher than that of existing superconducting magnets and large-scale hybrid magnets. Through detailed numerical simulations, the HTFML device is considered for the magnetic separation of a mixture of precious metal particles (Pt, Au, Ag, and Cu) dispersed in pure water, by exploiting the magneto-Archimedes effect. The HTFML can be realized as a compact and mobile desktop-type superconducting bulk magnet system, and there are a wide range of potential industrial applications, such as in the food and medical industries.

Enhancement of trapped field of REBCO bulk in a desktop-type magnet system

We developed a desktop-type bulk magnet system using a Stirling refrigerator and used it to study how to improve the trapped field by pulsed field magnetization (PFM). Although PFM has the advantage that the bulk is activated in a few seconds using an ordinary inexpensive equipment, the amplitude of a trapped field is low as compared with the maximum performance of the material. This paper aims to improve the trapped field by changing the size of soft-iron yoke, which are generally used to extend the pulse width. When a ϕ60-mm GdBCO bulk was magnetized using ϕ64-mm and ϕ80-mm yokes, the maximum flux density and total magnetic flux of large yoke were 13% and 23% higher than those of small one, respectively. Moreover, improvement of trapped field by multi PFM was investigated. When a magnetic field of 5.8 T was applied twice, the maximum trapped field of 1.46 T and the total magnetic flux of 1.86 mWb were achieved.

Improvement of the trapped field of REBCO bulk activated by pulsed field magnetization with a large soft-iron yoke

We study to increase the trapped magnetic field of a REBCO bulk magnet excited by pulsed field magnetization (PFM). In PFM, a soft-iron yoke is used to expose the bulk to the magnetic field for a long time. Although a small yoke 40 mm in diameter was used in our previous study, it was changed to a large yoke 64 mm in diameter in this paper. Accordingly, the pulse width was extended by 13%. When a GdBCO bulk 60 mm in diameter and 20 mm thick was magnetized by varying an amplitude of the applied field and temperature in a bulk magnet system using a two-stage GM-type refrigerator with a cooling capacity of 12 W at 20 K, the maximum trapped flux density reached 4.07 T on the center of the bulk surface and 2.56 T on the pole surface at 20 K. Moreover, the total magnetic flux was 3.28 mWb, which was about 13% larger than that of a small yoke. This result suggests that this method is useful in practice because the trapped field can be enhanced only by changing the soft-iron yoke.

Improvement of Trapped Magnetic Field of a REBCO Bulk Magnet Activated by Pulsed Field Magnetization in a High-Cooling Power Two-Stage GM-Type Refrigerator

We developed a high-cooling power bulk magnet system using a 12 K two-stage Gifford-McMahon (GM)-type refrigerator with a cooling ability of 12 W at 20 K in our previous study. When a single pulsed field was applied using a GdBCO bulk, the maximum trapped field of 3.59 T at the center of sample surface and the total magnetic flux of 2.89 mWb were achieved. In this paper, we aim to improve the trapped magnetic field by increasing the size of soft-iron yoke. When the same experiment was carried out using the same bulk, the trapped field was increased to 3.85 T. Moreover, the total magnetic flux reached a value of 3.97 mWb by a multipulsed field magnetization.

Promising effects of a new hat structure and double metal ring for mechanical reinforcement of a REBaCuO ring-shaped bulk during field-cooled magnetisation at 10 T without fracture

We have investigated a new reinforcement hat structure for a RE-Ba-Cu-O (REBaCuO, RE: rare earth element or Y) ring-shaped bulk superconductor (ring bulk) shrink-fitted with a double Al alloy ring and set on the cold stage of a cryogenic refrigerator prior to field-cooled magnetisation (FCM). With the hat structure, a ring bulk having an outer diameter of 64 mm, inner diameter of 40 mm, and height of 20.5 mm achieved a trapped field as high as 6.8 T at 50 K during FCM with an applied magnetic field at Bapp = 10 T without fracture; a similar ring bulk without the hat structure broke during FCM at Bapp = 8.8 T. Using a numerical simulation for electromagnetic and mechanical properties, the potential benefit of the hat structure was confirmed. The magnetic field dependence of the average critical current density Jc(B) of the ring bulk used in the simulation was determined by experimental results of time step dependence of the trapped field Bz at the bulk centre. As a result, the total hoop stress σθtotal in the ring bulk including the resulting stress of cooling from 300 K to 50 K and subsequent FCM at Bapp = 10 T is lower than the fracture strength of a typical Ag-doped REBaCuO bulk material. The effect of double Al alloy ring reinforcement was also analysed using a numerical simulation and compared with that of the conventional single Al alloy ring reinforcement. These results suggest that the double ring provides only a limited benefit, whereas the hat structure is fairly effective in reducing the electromagnetic hoop stress during FCM at Bapp = 10 T. Using this reinforcement method, a 400 MHz (9.4 T) nuclear magnetic resonance bulk magnet system could be realised.

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.

Comparison of Trapped Field Characteristic of Bulk Magnet System Using Various Type Refrigerators

We developed several type superconducting bulk magnets with the goal of their industrial application, and study to improve a magnetic field activated by pulsed field magnetization (PFM). When considering a practical use of bulk magnet, it is important problem to choose a suitable refrigerator to cool a bulk superconductor. This paper investigated trapped field characteristics when using several type refrigerators; one is a Stirling refrigerator with an ultimate temperature of 40 K at no-load condition and cooling capacity of 11 W at 77 K. The other is a dual-stage GM type refrigerator with the cooling ability of 13 K and 5 W at 20 K. Now, we developed a new bulk magnet system using a dual-stage GM refrigerator with the cooling ability of 12 K and 12 W at 20 K aiming to improve a trapped field by removing heat generated after a pulse application quickly. Using a GdBCO bulk with dimensions of 60 mm in diameter and 20 mm thick, magnetizing tests were carried out and the relationship between trapped field performance and cooling ability was investigated. Even the bulk magnet using Stirling refrigerator with relatively low cooling capacity could trap a high magnetic field of 3.0 T on the bulk surface and maximum total flux of 2.0 mWb. The trapped magnetic field of new bulk magnet system was improved greatly at low temperature; the maximum trapped field of 3.6 T and the maximum total flux of 2.9 mWb were achieved.

Enhancement of Trapped Magnetic Field Using a Large-Size REBCO Bulk in a Desktop Type Superconducting Bulk Magnet

We have developed a desktop type superconducting bulk magnet using a Stirling cryocooler with the aim of miniaturizing the magnet system. In our previous study, the lowest achieved temperature of 51.3 K and the maximum trapped field of approximately 2.8 T were achieved by cooling and magnetizing tests using a GdBCO bulk material 45 mm in diameter. For this paper, we remodeled the bulk magnet system in order to attach a large bulk 60 mm in diameter for the purpose of enhancing the total magnetic flux. This was based on the idea that the total magnetic flux was increased if the volume of the bulk was expanded, while we were concerned about the reduction of the trapped field due to the low cooling capacity of the refrigerator and the high ultimate temperature. When cooling and magnetizing tests were carried out using φ60-mm GdBCO bulk, the sample was cooled from room temperature to an ultimate temperature of 55.6 K for approximately 6.5 h, and the total magnetic flux was 2.0 mWb, which was approximately twice that of φ45-mm bulk, indicating that the aim of this study was achieved. The maximum trapped field was 3.0 T, which was the maximum value in pulsed-field magnetization using a large bulk at temperatures beyond 50 K.

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.

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 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.

Evaluation of Pulsed-Field Magnetization on a Superconducting Bulk Magnet System Using a 13 K Refrigerator

We developed a small-size superconducting bulk magnet system using a 13 K refrigerator. The industrial applications of bulk magnets demand the miniaturization of the magnet apparatus as well as the enhancement of the magnetic field. Downsizing of the apparatus can be achieved by restricting the magnetizing method to pulsed-field magnetization (PFM). PFM of a high-performance bulk, on the other hand, presents a difficult problem, i.e., large heat generation after the application of pulsed fields suppresses a trapped field. Therefore, a Gifford-McMahon cycle helium refrigerator with low ultimate temperature and large cooling capacity was adopted with the expectation to increase the Jc and quickly remove the heat. In a previous magnetizing test using a GdBa2Cu3O7-x bulk material, a trapped field of 2.76 T was achieved. In this paper, we evaluate a trapped field when applying a magnetic field of constant amplitude with varying temperature, and we used a multi-pulse technique with a stepwise cooling (MPSC) method in which several pulsed fields were applied as a function of the amplitude and temperature to improve the trapped field. We successfully trapped a magnetic field of 3.02 T.

Improvement of a magnetization method on a small-size superconducting bulk magnet system

A pulsed-filed magnetization (PFM) is an important technique for industrial applications of superconducting bulk magnets, and several advanced PFM methods are proposed to enhance the trapped field. In the well-known IMRA method, the channel through the magnetic flux is formed by the flux flow caused by heat generation when applying the strong pulsed-field, and the magnetic flux is made to penetrate into the bulk through the channel in the following pulse application. On the other hand, large applied field leads to large heat generation, and, therefore, the trapped field is decreased greatly.This paper proposes an effective magnetizing method in which the channel composed of magnetic field is artificially formed by field-cooling (FC) using a permanent magnet and the magnetic flux by PFM is induced to the channel. To confirm the validity of this method, the bulk was magnetized by FC using Nd–Fe–B magnets of the rectangular and the ring shapes, and thereafter, a pulsed-field of 6.2T was applied. As a result, the trapped field of the bulk magnetized by FC using the ring magnet was increased by about 20–25% as compared with that of the conventional PFM, and, moreover, it was observed that the channel was formed partially by measurement of the magnetic field distribution.

Development of Portable Superconducting Bulk Magnet System

A magnetic drug delivery system (MDDS) has recently been developed enabling magnetic seeded drugs to be navigated around the diseased parts of the human body. To improve the magnetic drug delivery performance, a portable superconducting bulk magnet system with strong magnetic fields has also been developed. This magnet system primarily consists of small bulk high-temperature superconductors and a compact Stirling-cycle cryocooler. The materials used in the high-temperature superconductors are rare earth 123 single domain compounds (GdBaCuO). The main body of the magnet is 9.5 kg and 740 mm in length. In this study, a bulk magnet was successfully activated using field-cooling magnetization under a superconducting solenoid magnet. The magnetic flux densities at the surface of the vacuum chambers that contain the bulk magnets reached 5.07 T and 6.76 T under the static fields of 6 T and 10 T, respectively. We clarified that the magnetic gradient was approximately 10 T/m at a position 50 mm from the surface of the vacuum chambers. This operating bulk magnet system is portable and can be easily transported via car over long distances.

Magnetic Separation of Nickel from Electroless Plating Waste Fluid using a HTS Bulk Magnet

A magnetic separation experiment to recycle nickel from the waste fluid of electroless plating processes was conducted using the open-gradient magnetic separation technique and a HTS bulk magnet system. A magnetic pole containing Gd123-based bulk superconductors was activated to 3.44 T at 34.9 K using a 5 T superconducting solenoid and the field cooling method. The coarse precipitates of nickel sulfate are composed of phosphite ions, which are yielded during the plating reaction by controlling the temperature and pH. Next, the open-gradient magnetic separation technique was employed, with use of water channels to separate the nickel-sulfate crystals from the mixture of the nickel sulfate and phosphite compounds based on the difference in magnetic properties. From the concentrations of each precipitate attracted to the magnetic pole, we succeeded in collecting nickel-sulfate crystals preferentially to the phosphite ions soon after crystal growth began.

Highly efficient magnetic separation using five-aligned superconducting bulk magnet

We have constructed the highly efficient magnetic separation system using five-aligned superconducting bulk magnets, which has ten usable magnetic poles on both sides in open space. We applied the bulk magnet system to the magnetic separation of ferromagnetic particles (magnetite; Fe3O4) and paramagnetic ones (α-hematite; Fe2O3) dispersed in water for various average particle diameters d, flow speeds VF and initial concentrations C0 of the particles. The multi-bulk magnet system has been confirmed to be effective for the magnetic separation and the efficiency of the magnetic separation per one magnetic pole has been estimated using the theoretical relation.

Development of a Small-Size Superconducting Bulk Magnet System Using a 13 K Refrigerator

We developed a small-superconducting bulk magnet system using a 13 K refrigerator. The industrial applications of bulk magnets demand the miniaturization of the magnet apparatus as well as the enhancement of the magnetic field. A Gifford-McMahon cycle helium refrigerator with the ultimate temperature of 13 K at the 2nd stage was adopted, and a bulk material of 60 mm diameter and 20 mm thickness reinforced by a stainless steel ring was located on a cold stage. When a magnetic field of 7.74 T was applied, the trapped field reached 2.76 T, which is the highest ever reported for a pulsed-field magnetization of 60 mm class bulk material.

Evaluation of magnetic force distribution on a pair of superconducting bulk magnets

We study the construction of superconducting permanent magnets by RE123 bulk materials and the investigation of these industrial applications such as a magnetic separation. A bulk magnet can generate strong magnetic fields exceeding 2T, which is the limit of ordinary iron-cored electromagnets, in a compact device with a low running cost. A magnetic field distribution of the bulk magnet is a cone shape, and it contributes to an increase of magnetic force which is proportional to the product of a magnetic field and its gradient. It is important to evaluate magnetic force when the application of the bulk magnet is discussed. In this paper, two Gd123 bulk materials of 65mm in diameter were magnetized using a pair of superconducting bulk magnet system and three-axis components of magnetic flux density (Bx,⋅By, and Bz) in an open space between the magnetic poles were scanned with pitch of 2mm in each direction. From these measured data, the axial and radial components of magnetic force factor, Bz⋅dBz/dz and Br⋅dBr/dr, were calculated. At 10mm gap, the Bz⋅dBz/dz value reached 180.6T2/m for a field of 2.33T, which is comparable to Bz=6.76T for a common 10T–100mm∅ superconducting magnet.