GdBaCuO Bulk Research Articles

Effects of Gd211 Ball-Milled by Stainless-Steel on Trapped Field of GdBaCuO Bulk

Effects of Gd211 Ball-Milled by Stainless-Steel on Trapped Field of GdBaCuO Bulk

Experimental study of a high-temperature superconducting induction/synchronous motor with REBCO bulk bars for transportation applications

Lightweight and highly efficient high-temperature superconducting (HTS) rotating electric machines show great potential for transportation applications. An advantage of RE-Ba-Cu-O (REBCO, where RE=rare earth) bulk superconductors over stacked HTS tapes is their ability to carry larger and more homogenous currents. This study is the first in which an HTS induction/synchronous motor (HTS-ISM) with Gd-Ba-Cu-O (GdBCO) bulk superconductors has been successfully designed, fabricated, and tested. Our fabricated prototype featured a squirrel-cage rotor wound with 44 GdBCO bulk bars that were embedded in the rotor iron and connected at both ends using Y-Ba-Cu-O (YBCO) tapes to form a short circuit. First, the critical current of the bulk sample was investigated under a magnetic field perpendicular to its top surface at 77 K. Subsequently, no-load and load tests were performed in liquid nitrogen at different frequencies to verify the performance of the prototype. Finally, we thoroughly analyzed the differences between the proposed HTS-ISM that utilizes GdBCO bulk bars and developed HTS-ISMs that utilize a few turns of YBCO or Bi-Sr-Ca-Cu-O (BSCCO) tapes per bar.

Dynamic guidance performance of GdBaCuO and YBaCuO bulk single grain superconductors under a varying external magnetic field

High temperature superconducting (HTS) maglev technology has attracted considerable attention from researchers around the world. It provides a new direction of development for urban rail and high-speed rail transit due to its considerable advantages of frictionless transportation, low noise, and environmental protection. HTS bulk materials are able to provide a significant performance advantage to maglev technology and are a key component to achieving both levitation and vehicle guidance. HTS bulk samples with enhanced flux pinning characteristics can enable improved curve negotiating ability and lateral stability for the maglev vehicle. This paper reports the results of experiments on the dynamic guidance force of single grain Y–Ba–Cu–O (YBCO) and Gd–Ba–Cu–O (GdBCO) bulk HTS single grains in order to explore their potential for enhanced maglev guidance performance. A customized HTS maglev dynamic measurement system (SCML-03) with a rotating, circular permanent magnet guideway (PMG) was employed to simulate the dynamic operation of the HTS vehicle above the PMG at different translational speeds. It was observed from the experimental results that the GdBCO bulk superconductor is more able to resist the attenuation of the dynamic guidance force compared to YBCO under the same operational conditions. In addition, the GdBCO bulk single grain is more able to return to the original equilibrium position following exposure to an external displacement. It is concluded that the GdBCO bulk single grain offers greater potential than YBCO for practical application in HTS maglev given its enhanced guidance performance. The results of these tests provide an important benchmark for the future design of HTS maglev transportation systems.

Waveform Control Pulse Magnetization of GdBaCuO Bulk Near Operating Temperature of Our Superconducting Rotating Machine

We have tested our waveform control pulse magnetization with negative feedback (WCPM-NFB) method on a GdBa <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> C <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">7-δ</sub> (GdBaCuO) high temperature superconducting (HTS) bulk sample, near operating temperatures of superconducting machines. This advanced single pulse field magnetization (PFM) method was demonstrated to significantly increase the trapped magnetic flux density in the center of the bulk compared to more conventional PFM techniques. The WCPM-NFB method has been further enhanced by modifying the control of the applied pulsed magnetic field. The aim was to adapt the control method to make use of the flux jump in a more efficient way while limiting the heat generation in the bulk. The target magnetic flux density of the PID controller was changed during the pulsed magnetization, allowing the applied magnetic field to be adapted consequently to the change of condition inside the bulk due to the flux jump. A magnetic flux density of about 3 T has been trapped at 50 K in a single pulse using our improved WCPM-NFB method.

Dynamic Guidance Performance of Gdbacuo and Ybacuo Bulk Single Grain Superconductors Under a Varying External Magnetic Field

Dynamic Guidance Performance of Gdbacuo and Ybacuo Bulk Single Grain Superconductors Under a Varying External Magnetic Field

Waveform Control Pulsed Magnetization of GdBaCuO Bulk Using Negative Feedback at 60 K

The practical use of high-temperature superconducting bulk electric rotating machines is limited, despite their increased power densities over permanent magnet machines, by the magnetization process of the bulks. A fast and effective magnetization process is needed to promote the practical application of superconducting machines. This is why we developed a method for magnetizing bulk superconductors and trapping high magnetic flux density using a single pulsed field magnetization (PFM). The method of magnetization of the superconducting bulk magnet by controlling the applied magnetic field has been tested previously at 77 K and 70 K. We tried during this study to trap high magnetic flux density in a GdBaCuO bulk at 60 K, to confirm that the method is effective at a lower temperature. Moreover, we tried to improve the method by using negative feedback of the magnetic flux density on the growth sector, to control the chopping of the current flowing through the magnetizing coils. We managed to reduce the temperature rise during the pulse by 10 K compared to a passive PFM and trapped a maximum of 2.17 T in the center of the bulk sample, the improvements compared to passive PFM at 60 K are remarkable.

Realisation of Hybrid Trapped Field Magnetic Lens (HTFML) consisting of REBCO bulk lens and REBCO bulk cylinder at 77 K

A hybrid trapped field magnet lens (HTFML) can reliably generate a concentrated magnetic field, B c, in the centre of the magnetic lens higher than the trapped field of the trapped field magnet (TFM) and the applied magnetic field, B app, even after the external magnetizing field decreased to zero. In this paper, the performance of HTFMLs consisting of EuBaCuO bulk TFM with various heights and a GdBaCuO bulk magnetic lens was investigated at 77 K using liquid nitrogen. A concentrated magnetic field of B c = 0.80 T was achieved at the centre of the HTFML for the tallest TFM after removing an applied magnetic field of B app = 0.50 T. The influence of the height of the outer TFM cylinder on the final concentrated field was studied experimentally and discussed using numerical simulation.

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.

Flux Dynamics and Thermal Behavior of a GdBaCuO Bulk Magnetized by Single- and Double-Pulse Techniques Using a Split-Type Coil

We have investigated the trapped field properties of a GdBaCuO disk bulk during single- and double-pulsed field magnetization (PFM) using a split-type coil for various pulse sequences for the first time. It is well known that the multi-PFM technique using a solenoid-type coil and the single-PFM technique using a split-type coil are effective to enhance the trapped field due to a lower temperature rise. However, it was found, in this work, that the trapped field by double-PFM using the split-type coil was not enhanced in spite of lower temperature rise. We analyzed the magnetizing process using two parameters, the “magnetic flux penetration ratio,” Rin, and the “magnetic flux residual ratio,” Rout, for various pulse sequences for the split-type and solenoid-type coils. The Rin value was decreased by the double-PFM for both coils, and the Rout value was improved only by the double-PFM using the solenoid-type coil. As a result, the trapped field for single-PFM using the split-type coil, which has a higher Rin, reduced after the double-PFM due to a decrease of Rin and no enhancement of Rout. These results are in clear contrast to those using the solenoid-type coil.

Trapped Field Properties of GdBaCuO Bulk Superconductors of Various Diameters Magnetized by Pulsed Fields Using an Identical Split Coil

In this paper, the trapped field properties of GdBaCuO disk bulk superconductors of various diameters during pulsed-field magnetization (PFM) using an identical split coil at 65 K have been investigated both experimentally and numerically. The maximum trapped field, B <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">T</sub> <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">max</sup> , of the φ43-mm bulk was larger than that of the φ30-mm bulk. However, B <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">T</sub> <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">max</sup> of the φ65-mm bulk was smaller than that of the φ43-mm bulk and the trapped field profile exhibited a distorted “C-shaped” profile. Using the numerical simulation, these results for the φ65-mm bulk can be explained by an inhomogeneous temperature profile and the larger generated heat, Q, due to the lower cooling power of the refrigerator compared to the generated heat. The important issues to achieve higher and homogeneous trapped fields are discussed when using split-coil PFM for larger bulks.

Magnetic levitation and guidance performance of Y–Ba–Cu–O and Gd–Ba–Cu–O bulk superconductors under low ambient pressure

The high-temperature superconducting Maglev-evacuated tube transport (HTS Maglev-ETT) system has significant potential for practical applications. In order to employ HTS bulks in an ETT system, it is necessary to study the magnetic levitation and guidance performance of bulk superconductors under low ambient pressure conditions that are representative of those inside the tube. As a result, we have investigated the Maglev performance of Y–Ba–Cu–O (YBCO) and Gd–Ba–Cu–O (GdBCO) single grain, bulk superconductors under different ambient pressures of 100 kPa, 60 kPa and 20 kPa using a bespoke pressure-controlling platform, in which the superconductors were positioned above a Halbach permanent magnet guideway. The levitation forces under conditions of field-cooling (FC) and zero-field-cooling (ZFC) have been measured and analyzed. The guidance force for the FC case and the levitation force relaxation for the ZFC case were also measured. It was found from the experimental results that the Maglev performance of both types of bulk superconductor improves significantly by reducing the ambient pressure in their immediate working environment. The levitation forces of YBCO and GdBCO bulk superconductors were observed to increase by 11.6% and 4.4% in the case of FC, and by 20.3% and 13.7% in the case of ZFC, respectively, as the ambient pressure changed from 100 kPa to 20 kPa. An improvement of the guidance force and an inhibition of the levitation force relaxation were also observed for these materials. The supercooled liquid nitrogen cryogen in the low-pressure environment further reduces the temperature, which, in turn, increases the critical current density Jc of the bulk superconductors and improves their levitation performance. These results provide further evidence of the significant advantages of combining HTS Maglev with evacuated tube technologies as a key enabling feature of the HTS Maglev-ETT system. The data further indicate that YBCO bulk superconductors tend to be more sensitive to ambient pressure and temperature variation than GdBCO bulk superconductors. This difference essentially reflects the dependence of Maglev performance of HTS bulk superconductors on Jc when operating in a low-pressure environment.

Levitation Force of Bulk YBaCuO and GdBaCuO Under a Low-Pressure Environment

The high-temperature superconducting (HTS) bulk is the core component of HTS maglev systems. For the potential application of evacuated tube transportation, it is necessary to verify the loading capacity of the bulk under a low-pressure environment. Based on a home-made pressure-reducing platform, we investigated the levitation force of two kinds of typical bulks, that is, the same sized YBaCuO and GdBaCuO, above a Halbach permanent magnet guideway under different pressure conditions. The levitation force in the cases of zero-field-cooling (ZFC) and field-cooling (FC) were measured and analyzed. Experimental results show that the reduced air pressure can significantly improve the levitation force of the two kinds of bulks. The levitation force of YBaCuO and GdBaCuO has increased by 11.6% and 4.4% in the FC case, 20.3% and 13.7% in the ZFC case under 20 kPa compared with the atmospheric pressure (100 kPa), respectively. This universal phenomenon was explained by the increasing critical current density Jc of HTS bulks due to cooler liquid nitrogen under the low-pressure condition. It is interesting to find that the YBaCuO bulk was more sensitive to the pressure variation compared with the GdBaCuO bulk. This difference reflects the improvement extent of levitation force of HTS bulks with different Jc performance working in a low-pressure environment.

Dynamic levitation performance of Gd–Ba–Cu–O and Y–Ba–Cu–O bulk superconductors under a varying external magnetic field

We report that the dynamic levitation force of bulk high temperature superconductors (HTS) in motion attenuates when exposed to an inhomogeneous magnetic field. This phenomenon has significant potential implications for the long-term stability and running performance of HTS in maglev applications. In order to suppress the attenuation of the levitation force associated with fluctuations in magnetic field, we compare the dynamic levitation performance of single grain Y–Ba–Cu–O (YBCO) and Gd–Ba–Cu–O (GdBCO) bulk superconductors with relatively high critical current densities. A bespoke HTS maglev dynamic measurement system (SCML-03) incorporating a rotating circular permanent magnet guideway was employed to simulate the movement of HTS in a varying magnetic field at different frequencies (i.e. speed of rotation). The attenuation of the levitation force during dynamic operation, which is key parameter for effective maglev operation, has been evaluated experimentally. It is found that GdBCO bulk superconductors that exhibit superior levitation force properties are more able to resist the attenuation of levitation force compared with YBCO bulk materials under the same operating conditions. This investigation indicates clearly that GdBCO bulk superconductors can play an important role in suppressing attenuation of the levitation force, therefore improving the long-term levitation performance under dynamic operating conditions. This result is potentially significant in the design and application of HTS in maglev systems.

A portable magnetic field of &amp;gt;3 T generated by the flux jump assisted, pulsed field magnetization of bulk superconductors

A trapped magnetic field of greater than 3 T has been achieved in a single grain GdBa2Cu3O7-δ (GdBaCuO) bulk superconductor of diameter 30 mm by employing pulsed field magnetization. The magnet system is portable and operates at temperatures between 50 K and 60 K. Flux jump behaviour was observed consistently during magnetization when the applied pulsed field, Ba, exceeded a critical value (e.g., 3.78 T at 60 K). A sharp dBa/dt is essential to this phenomenon. This flux jump behaviour enables the magnetic flux to penetrate fully to the centre of the bulk superconductor, resulting in full magnetization of the sample without requiring an applied field as large as that predicted by the Bean model. We show that this flux jump behaviour can occur over a wide range of fields and temperatures, and that it can be exploited in a practical quasi-permanent magnet system.

Trapped magnetic-field properties of prototype for Gd-Ba-Cu-O/MgB2 hybrid-type superconducting bulk magnet

We have studied experimentally and numerically the trapped magnetic-field properties of a hybrid-type superconducting bulk magnet, which comprised an inner Gd-Ba-Cu-O (GdBCO) disk-bulk and an outer MgB2 ring-bulk, under field-cooled magnetization (FCM) and pulsed-field magnetization (PFM). The trapped field by FCM at the center of the hybrid bulk was 4.5 T at 20 K, which was 0.2 T higher than that of the inner GdBCO disk-bulk without MgB2 ring-bulk. The experimental results by FCM were quantitatively reproduced by the numerical estimations for a model, which makes it possible to understand the trapped field properties of the hybrid bulk. The total magnetic flux by FCM, which was estimated numerically, was enhanced by about 1.7 times from 0.91 mWb of the single GdBCO bulk to 1.53 mWb of the hybrid bulk. We also succeeded in magnetizing the whole hybrid bulk by applying multi-pulsed-fields. The central trapped field of 1.88 T was not enhanced, but the total magnetic flux, which was obtained experimentally, was evidently increased by 2.5 times (0.25 0.62 mWb) for the hybrid bulk. The obtained results suggest that the hybridization is effective to enhance the total magnetic flux. To confirm the reinforcing effect of the MgB2 ring to the GdBCO disk during the cooling and magnetization processes, we have measured the thermal dilatation, , of the GdBCO, MgB2 and stainless steel. As a result, the thermal dilatation of MgB2 was smaller than that of GdBCO. MgB2 ring-bulk shows no compression effect to resist the hoop stress of the GdBCO disk-bulk during the FCM process. The reinforcing material such as the stainless steel ring must be set outside the GdBCO disk-bulk.

The fabrication process of a high performance and pure c-axis grown GdBCO bulk superconductor with the TSMT-IG technique

It is very important to choose a suitable seed crystal in the fabrication process of the (RE)BCO bulk superconductors by the top-seeded growth method, because a defective seed would result in the failure of the entire sample. Therefore, for optimizing the seed, a new approach is proposed in this paper for the fabrication process of Gd-Ba-Cu-O (GdBCO) bulk with promising superconducting properties. We developed the top-seeded melt texture and infiltration growth (TSMT-IG) process based on the modified top-seeded infiltration and growth (TSIG) process. In this modified infiltration growth, a mini pellet of thin melting texture (TMT) GdBCO was inserted between the NdBCO seed crystal and the solid-phase precursor pellet, resulting in the successful formation of well purified c-axis-oriented GdBCO crystals with a proper-sized TMT layer. The growth morphology, microstructure, side growth boundary, and superconducting properties of the GdBCO bulk superconductors with three different sizes of TMT pellets were studied in this paper. The results proved that the success rate for the fabrication of single-domain GdBCO bulk superconductors can be improved by the TSMT-IG process, which can also effectively inhibit the random nucleation phenomenon at some extent during the process of single-domain GdBCO bulk superconductor growth. In addition, the application of this new growth technology can help us not only to improve the growth performance of GdBCO samples with a proper size of the TMT mini pellet but also reduce the fabrication cost due to the use of only one precursor powder.

3-D Numerical Evaluation of Trapped Magnetic Field and Temperature of a Rectangular GdBaCuO Bulk Magnetized by MMPSC Method

In this paper, numerical simulations of trapped field and temperature rise in a bulk superconductor during magnetization process are studied. The pulsed field magnetization method and the modified multi-pulse technique with stepwise cooling are presented. We adopt the control volume method for solving the thermomagnetic system describing the physical phenomena. The electromagnetic fields and temperature are computed because of an explicit algorithm. The results are compared with published experimental results and show a good concordance.

Multi-seeded growth of melt processed Gd–Ba–Cu–O bulk superconductors using different arrangements of thin film seeds

Gd–Ba–Cu–O (GdBCO) bulk superconductors of diameter of 42mm have been fabricated via a multi-seeded melt growth (MSMG) method in air using well-oriented Nd–Ba–Cu–O thin film seeds. The effect of seed orientation on the growth process and the formation of grain boundaries were investigated systematically by using two thin film seeds arranged with crystallographic orientations of (100)/(100) and (110)/(110), respectively. The multi-seeded process was then firstly extended to four thin film seeds arranged asymmetrically [(110)/(110)], which involved placing the seeds in pairs, with two adjacent seeds positioned relatively close to each other and the other two at a greater separation. This modified technique is beneficial to obtain a large size GdBCO bulk in a shorter time as well as clean grain boundaries by rejecting the excess melt liquid thoroughly along the growth front. More interestingly, a domain of non-equilibrium shape is formed during the MSMG process, which leads potentially to the growth of much larger samples. The growth mode of the enhancement in growth rate is interpreted by the presence of a high index crystallographic (110) face to the initial growth front.

Magnetic field, temperature and mechanical crack performance of a GdBCO magnetic lens

Magnetic field concentration by using the diamagnetism of a superconductor is a novel technique that has been experimentally demonstrated in magnetic lenses. A magnetic lens consists of a hollow superconductor cylinder with a tapered inner diameter within which the magnetic flux is concentrated by diamagnetism. Magnetic lenses are very promising for use in compact high magnetic field systems. However, magnetic lenses with large inner diameters are required to facilitate sample access during use. In this study, an optimized GdBaCuO magnetic lens with large inner and outer diameters was designed and its performance was investigated in liquid nitrogen, liquid helium, and a cryocooler-cooled cryostat. A lens with an inner diameter of 12 mm was constructed by stacking three specially machined GdBaCuO bulk pieces. This magnetic lens cracked due to the large flux jump that occurred when the concentrated field of the magnetic lens exceeded 10 T at 4.2 K. The cracked lens was subsequently impregnated with epoxy resin. A concentrated field of 12.42 T was realized when the background field was 8 T at 20 K and no flux jumps occurred. This result demonstrates that this GdBCO magnetic lens is promising for use in compact superconducting magnet systems.

Magnetic Shielding Characteristics of Multiple Bulk Superconductors for Higher Field Applications

High performance (RE) BaCuO bulk superconductors are now available and can be used as a strong magnet or a good magnetic shield. There are a variety of potential magnetic shielding applications using bulks. Magnetic shielding characteristics and size of bulk superconductors are the key issues to realize these applications. In this paper, magnetic shielding experiments using GdBaCuO bulk superconductors at 77 K are reported. Multiple bulk super conductors are arrayed and stacked in layers to obtain a large magnetic shield. We successfully obtained a uniform magnetic shielding area with properly arranged three layers of tiled bulks at 0.1 T, 77 K. We also discuss the magnetic shielding characteristics for different external magnetic fields strengths.