GdBCO Bulk Research Articles

The levitation force and stiffness enhancement of single domain GdBCO bulk superconductor by an axial background magnetic field

How to improve the levitation force (FL) and its stiffness between a permanent magnet and a REBCO bulk superconductor is one of the most key and attractive problems to be solved for practical applications. In this paper, we provided a novel hybrid magnet added superconductor system (HMS) to enhance the levitation force and the stiffness, the HMS sample is assembled by a single domain GdBCO bulk with an attached permanent magnet (PM) serving as an axial background magnetic field. The results indicate that (1) the FL increased first and decreased then with the increase of the PM diameter (dPM), the largest FL is achieved when the dPM approaches the diameter of the GdBCO bulk, FL has been improved up to 152% with a thinner PM; (2) the FL increased with the increase of the PM thickness and saturated at a certain value, FL have been improved up to 168% with a thicker PM; (3) the stiffness of FL has been improved up to 187% and 201% with the increase of the PM diameter and thickness; (4) the FL and its stiffness enhancement dependent on the positive trapped field of the field cooled HMS samples. The results are of great significance to improve the performance and stability of maglev systems, the mechanism for enhancing the levitation force and stiffness property has been investigated in details.

Study on the PFM Behavior of GdBCO Bulk Joined by ErBCO and Its FEM Simulation

Study on the PFM Behavior of GdBCO Bulk Joined by ErBCO and Its FEM Simulation

R-z plane spatial critical current inhomogeneity-induced mechanical response of GdBCO superconducting bulks during field cooling magnetization

Benefiting from the high critical current density (J c), single-grain (RE)BCO (where RE = rare earth or Gd) bulks are capable of trapping over 17.6 T magnetic field which is crucial for the application of bulk superconductors. Nevertheless, during field cooling magnetization (FCM), the large mechanical stress induced by Lorentz forces may lead to fracture behavior in the brittle ceramic nature of (RE)BCO materials. Most previous numerical models that adopted simplified homogeneous J c had difficulty reflecting the real stress/strain situation in high temperature superconductor (HTS) bulks. Based on the proposed modified Jirsa model considering r-z plane J c inhomogeneity, we investigate the mechanical response of GdBCO bulks manufactured by top-seeded melt growth (TSMG) process. A 2D axisymmetric electromagnetic-thermal-mechanical coupled model is implemented to take into account the dependence of J c upon mechanical deformation. The simulation results show the electromagnetic-thermal-mechanical response of the r-z plane inhomogeneous J c model is lower than that obtained by the homogeneous J c model. This confirms Takahashi’s speculation (K Takahashi 2019 Supercond. Sci. Technol. 32 015007) about the mismatch between experimental data and the simulation results of homogeneous J c model, and suggests the stress levels in the bottom plane of HTS bulk are overestimated by the previous homogeneous J c model. On top of that, the overall stress level of GdBCO bulk is strongly determined by the magnitude and position of the Lorentz force load, and the stress distribution of inhomogeneous J c model is mainly concentrated in high J c regions near top surface, instead of being symmetrically distributed along the z-axis as in homogeneous J c model. The mechanical response of stainless steel reinforced GdBCO bulk was aslo simulated and analyzed. Finally, the coupling effect between the fracture strength variability caused by defects and cracks and the trapped field in GdBCO bulks with r-z plane J c inhomogeneity is further studied. This study may provide a relatively realistic mechanical response of HTS bulk during FCM, and a novel design consideration for its mechanical reinforcement.

Enhanced performance of GdBCO bulk superconductors by doping a new kind of YGdBa4CuNbO y nanoparticles

In this work, a new kind of YGdBa4CuNbO y (YGdNb-11411) nano-particles was designed and sintered using a solid-state reaction method, whereas their impact on the performance of GdBCO bulks was investigated for the first time. From the acquired x-ray diffraction data and scanning electron microscopy imaging results, it was proved that the YGdNb-11411 particles were of excellent chemical stability and did not react with other phases during the crystal growth process. The YGdNb-11411 particles ranged from 80 to 130 nm and they were uniformly distributed in the well-textured GdBCO bulk superconductors. The maximum critical current density (J c-max) of the samples was enhanced from 3.48 × 104 A cm−2 to 8.63 × 104 A cm−2 (77 K) in the self-field as the doping amount increased from 0 wt% to 7 wt%. In addition, the GdBCO sample with YGdNb-11411 particles also showed an enhanced flux pinning force density and relatively high J c around the magnetic flux density range of 1 T–2 T (77 K). These results clearly indicated that the YGdNb-11411 particles could effectively enhance the properties of the GdBCO bulk superconductors.

GdBCO bulk superconducting helical undulator for x-ray free-electron lasers

GdBCO bulk superconducting helical undulator for x-ray free-electron lasers

The Performance of the Two-Seeded GdBCO Superconductor Bulk with the Buffer by the Modified TSMG Method.

The multiseeding technique is a method to grow large-sized REBa2Cu3O7-δ (REBCO, where RE is a rare earth element) high temperature superconducting bulks. However, due to the existence of grain boundaries between seed crystals, the superconducting properties of bulks are not always better than those of single grain bulks. In order to improve the superconducting properties caused by grain boundaries, we introduced buffer layers with a diameter of 6 mm in the growth of GdBCO bulks. Using the modified top-seeded melt texture growth method (TSMG), that is, YBa2Cu3O7-δ (Y123) as the liquid phase source, two GdBCO superconducting bulks with buffer layers with a diameter of 25 mm and a thickness of 12 mm were successfully prepared. The seed crystal arrangement of two GdBCO bulks with a distance of 12 mm were (100/100) and (110/110), respectively. The trapped field of the GdBCO superconductor bulks exhibited two peaks. The maximum peaks of superconductor bulk SA (100/100) were 0.30 T and 0.23 T, and the maximum peaks of superconductor bulk SB (110/110) were 0.35 T and 0.29 T. The critical transition temperature remained between 94 K and 96 K, with superior superconducting properties. The maximum JC, self-field of SA appeared in specimen b5, which was 4.5 × 104 A/cm2. Compared with SA, the JC value of SB had obvious advantages in a low magnetic field, medium magnetic field and high magnetic field. The maximum JC, self-field value appeared in specimen b2, which was 4.65 × 104 A/cm2. At the same time, it showed an obvious second peak effect, which was attributed to Gd/Ba substitution. Liquid phase source Y123 increased the concentration of the Gd solute dissolved from Gd211 particles, reduced the size of Gd211 particles and optimized JC. For SA and SB under the joint action of the buffer and the Y123 liquid source, except for the contribution of Gd211 particles to be the magnetic flux pinning center with the improvement of JC, the pores also played a positive role in improving the local JC. More residual melts and impurity phases were observed in SA than in SB, which had a negative impact on the superconducting properties. Thus, SB exhibited a better trapped field and JC.

A novel method for fabricating of high-performance multi-seeding GdBCO bulk superconductors

A novel multi-seeding (NMS) method is proposed for improving the performances of GdBCO samples by optimizing the shapes and the space configurations of the single-domain GdBCO grains. Three multi-seeding GdBCO bulk superconductors with dimensions of 60 × 20 × 14 mm3 were fabricated by a Gd + 011 infiltration growth method with different seeding techniques: samples S1 and S2 by the traditional multi-seeding method (TMS) with two and three seeds, respectively; and sample S3 by the NMS method with three seeds. The results show that among the three, sample S3 has both of the largest levitation force, 111 N, and the largest magnetic field coupling ratio, 68.57%, which are clearly higher than the levitation force of 100 N and 90 N, and the magnetic field coupling ratios of 34.25% and 11.33% for the samples S1 and S2, respectively. These results indicate that the NSM method is a useful way to improve the mechanical strength, homogeneity, and performances of multi-seeding GdBCO samples.

Effect of stacking height on the levitation force and trapped field properties of GdBCO bulk superconductor

Effect of stacking height on the levitation force and trapped field properties of GdBCO bulk superconductor

A low-cost approach for recycling large GdBCO bulk superconductors using an infiltration technique with different liquid sources

The high-temperature superconductor has become a research hotspot, because of its high critical temperature, strong trapped flux density, stable suspension characteristics and large magnet levitation force. Single-domain REBa2Cu3O7−δ (REBCO) superconductors, where RE is a rare-earth element such as Y, Gd, Sm or Nd, have wide and potential applications in high-tech fields, such as micro-magnet superconducting maglev trains, superconducting motors and superconducting magnetic separation systems. However, a large number of multi-domain samples are easily produced in the preparation process, resulting in a significantly lower success rate and a significant increase in cost, which restricts their practical applications. Thus, we successfully recycle a series of GdBCO samples by re-supplementing the liquid phase lost in the primary growth process and pre-treating the failed sample as solid-phase source billets, which was proposed by Shi. The growth morphology and superconducting properties of the recycled GdBCO bulk superconductors are investigated in detail in this study. The results show that the key superconductivity properties have been significantly improved, which provides the scientific basis and new ideas for the development of low-cost and highly efficient fabrication yields of REBCO bulk superconductors.

Development of homogeneous and high-performance REBCO bulks with various shapes by the single-direction melt growth (SDMG) method

We have developed a single-direction melt growth method in which REBCO melt-textured bulks grow only vertically from a seed plate utilizing the difference in peritectic temperatures of REBCO. Entirely c-grown YBCO, DyBCO and GdBCO bulks with various sizes and shapes were successfully fabricated with high reproducibility. Disk-shaped bulks showed high trapped fields with almost concentric field distributions, reflecting homogeneous and boundaryless bulk structures. In particular, a YBCO bulk with a 32 mm diameter trapped a high field more than 1 T at 77 K. Furthermore, rectangular and joined hexagonal REBCO bulks were successfully fabricated, showing designed field-trapping distributions reflecting their shapes through well-connected superconducting joints among bulks.

Flux Pinning Properties of Single-Grain Bulk GdBCO Superconductors Processed by Different Thicknesses of Y123 Liquid Source.

The performance of critical current density of GdBa2Cu3O7−δ (GdBCO or Gd123) superconductor bulk has an important influence on its practical applications. In this work, four single-domain GdBCO superconductor bulks were successfully processed by the modified top-seeded melt-texture growth method. The addition of a YBa2Cu3O7−δ (Y123) liquid source with different thicknesses, 0 mm (S0), 3 mm (S3), 5 mm (S5), 7 mm (S7), was introduced to study the influence on the superconducting properties. GdBCO bulk with the addition of the Y123 liquid source with a 3-mm thickness shows the best superconducting properties. The addition of the Y123 liquid source results in a decrease in the Gd3+ ion concentration required for Gd123 growth; thus, Gd2BaCuO5 (Gd211) particles in the liquid source need a larger self-decomposition to diffuse Gd3+ ions to Gd123 growth front, which refines the size and leads to a homogenous distribution of the Gd211 particles in the bulks. Thus, the more pinning centers of fined Gd211 particles improve the superconducting properties of GdBCO bulk. With increases in the thickness of Y123 liquid source to 5 mm and 7 mm, high RE3+ (Gd3+ and Y3+) concentration can coarsen Gd211 particles and fuse with Gd211 liquid source. The superconducting properties apparently drop. Therefore, the addition of a Y123 liquid source with a suitable thickness is a positive modification to obtain high-performance GdBCO bulk.

The magnetic and levitation characteristics of single-grain YBaCuO and GdBaCuO-Ag bulk superconductors in high magnetic fields

In principle, high-temperature superconducting (HTS) flux-pinning maglev has the advantage of self-stable levitation and is therefore a good development prospect as a new rail transit technology. The magnetic field intensity is one of the key factors affecting the levitation performance of single-grain bulk superconductors in the HTS maglev system. To date, however, most researchers have focused on the levitation performance of HTS bulk superconductors in magnetic fields within a permanent magnet guideway (PMG) configuration. The magnitude of the external working magnetic field provided by a PMG is limited to about 0.5 T at 77 K, given that the superconductor usually levitates at a typical working height of 10 mm above the PMG. Therefore, the weak magnetic fields generated by the PMG significantly limits the levitation performance of HTS maglev systems to that of the permanent magnet (PM). In this article, a superconducting magnet test bench was utilized to provide a 0–3 T external magnetic field (B) environment for the study of the levitation force in HTS single grains. The difference in levitation performance between YBaCuO (YBCO) and GdBaCuO-Ag (GdBCO-Ag) bulk superconductors under large, changing magnetic fields was studied systematically. The relationships between levitation force and magnetic field characteristics, including vertical magnetic field component (Bz), transverse magnetic field component (Br), and vertical magnetic field variation (ΔBz) were investigated. The result of variation curves about YBCO and GdBCO bulks' levitation forces under different ΔBz shows that the levitation force of the bulk, single-grain superconductors will reach saturation under a varying ΔBz environment (0.72 and 1.5 T). The values of ΔBz corresponding to the saturation positions are found to be independent of the sizes of the HTS samples. At the same time, GdBCO-Ag exhibits a levitation force that is 112.8% greater than YBCO in B = 3 T magnetic environment. As a result, it is demonstrated that the levitation potential of single-grain HTS bulks can be better exploited by optimizing the distribution of the magnetic field.

Trapped field evaluation of ring-shaped GdBCO bulk magnet excited by pulsed field magnetization

Recently, physical and mechanical properties of REBCO bulk are improved, and, accordingly, various practical applications are considered. As one of them, a portable bulk NMR system has been developed, and, then, the improvement of the system for practical use are progressing. In that system, 6 stacked bulks were magnetized by a superconducting magnet for NMR, resulting that the magnetic field of 4.74 T and inhomogeneity of 6.9 ppm were achieved. In this paper, we fabricated the bulk magnet with the room-temperature bore specialized in pulsed-field magnetization. The ring-shaped bulk was activated by pulsed-field magnetization, and, magnetic fields on the bulk surface and in the room-temperature bore of bulk magnet were evaluated. In the bore, the trapped field was approximately 0.79 T and homogeneity was over 150000 ppm.

Fabrication process and superconducting properties of recycling multi-domain GdBCO bulk superconductors using improved infiltration technique

High temperature superconductor has become one of the hotspots of research, because of its high critical temperature, strong trapped flux density, stable suspension characteristics and large magnet levitation force. The single domain REBa<sub>2</sub>Cu<sub>3</sub>O<sub>7–<i>δ</i></sub> (REBCO) superconductors have the wide and potential applications in the high-tech fields, such as micro-magnet superconducting maglev train, superconducting motor and superconducting magnetic separation system. However, a large number of multi-domain samples are easy to produce in the preparation process, which leads the success rate to decrease significantly and the cost to increase considerably, which restricts its practical application process. Inspired by the top seeded infiltration growth method, we develop a reliable method of recycling failed GdBCO sample by re-supplementing the liquid phase lost in the primary growth process and pretreating the failed sample as solid phase source billets. We recycle a series of GdBCO samples by using this new technique successfully. The growth morphology, superconducting properties, and microstructures of the recycled GdBCO bulk superconductors are investigated in detail in this study. The results show that the magnetic levitation forces of the recycled GdBCO samples are all greater than 30 N, their magnetic flux densities are all above 0.3 T, and their capture efficiencies are above 60%. These results provide the scientific basis and new ideas for developing the low cost and high efficient yield of fabrication of the REBCO bulk superconductors.

A New Method for Batch Production of Single Domain GdBCO Bulks of Different Growth Sectors Using One Seed by the RE+011 TSIG Process

A single domain REBCO bulk, fabricated with one seed whether by the top seeded melt growth method or top seeded infiltration growth (TSIG) process, consists of five growth sectors (GSs) generally. ...

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.

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.

Improvement of trapped magnetic field in GdBCO by waveform control pulse magnetization at 70 K

We attempted to trap a strong magnetic field with a single pulsed magnetic field by applying waveform control pulse magnetization (WCPM) method to a high-temperature superconductor (HTS) bulk sandwiched between two vortex-type copper coils at less than 77 K. The GM cryocooler conductively cooled the GdBCO bulk to 70 K in an arrangement similar to the internal structure of our axial gap type HTS motor. The HTS bulk showed no flux jump, while the duty ratio of WCPM was small. When we increased the duty ratio, we found a flux jump without looking at any prior signs and the trapped magnetic flux density increased twice. Hence we attempted a negative feedback WCPM with the control target at the highest trapped magnetic flux density while no flux jump was found. After trial and error of control conditions, the HTS bulk sample trapped a maximum magnetic flux density of 1.79 T by a single pulse magnetic field. If the WCPM technique is used, a single pulse magnetic field will cause the HTS bulk to obtain a higher trapped field at lower temperatures.

A Practical Processing Method for the Fabrication of NdBCO Seed Crystals and High-Performance Single-Domain GdBCO Bulk Superconductors

NdBCO seed crystals and high-performance GdBCO bulk superconductors were prepared successfully by a modified top-seeded melt-textured growth (TSMG) process and by Gd + 011 top-seeded infiltration growth (TSIG) process. The modified TSMG process used a new composition powder (NCP, 0.9 Nd2O3 + 2.4 BaCuO2 + CuO) instead of the conventional composition powder (CCP, NdBa2Cu3O7-x + 0.4 Nd2BaCuO5), the GdBCO bulk superconductor seeded by the self-made NdBCO seed crystal. In the whole procedure above, only one precursor powder (BaCuO2) needs to be sintered, three kinds of powder and three pellets are required, so time and energy consumption were greatly reduced. The results of thermal analysis and X-ray diffraction (XRD) patterns revealed the reaction mechanism of the modified TSMG process. Superconductivity properties of the GdBCO sample were measured employing a levitation force measurement system and a vibrating-sample magnetometer (VSM); the maximum value of the levitation force of the GdBCO sample was 44.78 N (77 k, 0.5 T); the onset superconductivity transition temperature (Tc) was approximately 93.7 K; the transition width was 6.2 K, and the maximum value of critical current density (Jc) was 1.5 × 105 A∙cm−2 (0 T, 77 K). These results indicate that, by combing the modified TSMG process and Gd + 011 TSIG process, a practical processing method for preparing the NdBCO seed crystals and the high-performance single-domain GdBCO bulk superconductors was developed.

The comparison of levitation and lateral force of bulk and cut-pasted bulk GdBCO samples at different temperatures

In this work, in the first time, we have investigated the levitation and lateral force properties of bulk and cut-pasted bulk GdBCO samples at different temperatures and different cooling heights (CH) to determine the effect of cut-pasted process on the magnetic levitation force behaviour. The measurements of superconducting characteristics indicated that the attractive and repulsive force values of cut-pasted GdBCO sample are slightly lesser than those of GdBCO bulk sample. The maximum repulsive and attractive force values obtained as 15.45 N and −4.56 N for GdBCO bulk and as 14.78 N and −3.92 N for cut-pasted GdBCO samples at 37 K. Although there are many fabrication methods as melt-textured growth (MTG), top seeded infiltration growth (TSIG) and TSMG to produce large HTS samples, the desired large sample size and the sample shape compatible with the superconducting magnetic bearing systems are not still sufficient for the technological applications. In this study, the performed cut-pasted process and obtained magnetic levitation force data can be using for the increment sample size and the desired sample shape in the needed different geometry and size for superconducting magnetic bearing systems.