Article

A Trapped Field of 17.6T in Melt-Processed, Bulk Gd-Ba-Cu-O Reinforced with Shrink-Fit Steel

Article

A Trapped Field of 17.6T in Melt-Processed, Bulk Gd-Ba-Cu-O Reinforced with Shrink-Fit Steel

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Abstract

The ability of large grain, REBa$_{2}$Cu$_{3}$O$_{7-\delta}$ [(RE)BCO; RE = rare earth] bulk superconductors to trap magnetic field is determined by their critical current. With high trapped fields, however, bulk samples are subject to a relatively large Lorentz force, and their performance is limited primarily by their tensile strength. Consequently, sample reinforcement is the key to performance improvement in these technologically important materials. In this work, we report a trapped field of 17.6 T, the largest reported to date, in a stack of two, silver-doped GdBCO superconducting bulk samples, each of diameter 25 mm, fabricated by top-seeded melt growth (TSMG) and reinforced with shrink-fit stainless steel. This sample preparation technique has the advantage of being relatively straightforward and inexpensive to implement and offers the prospect of easy access to portable, high magnetic fields without any requirement for a sustaining current source.

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... with carbon fibre fabric, which achieved 17.24 T between two samples in a stack configuration [7]. (b) Photograph of 24 mm diameter GdBCO/Ag discs enclosed in shrink-fit stainless-steel rings, which achieved 17.6 T between the two samples [8]. (c) A portable, single pole bulk magnet system that can generate over 2 T on the surface [64]. ...
... The curves have been extended to 10 T using the equation presented by Jirsa et al. [126]. The data were input into the model using [135] (b) 16 mm diameter TSMG YBCO manufactured by Chaud et al. [136] (c) YBCO grown using a modified infiltration growth technique by Li et al. [138] [8], which is an order of magnitude higher than the maximum field attainable by conventional permanent magnets (permanent magnets are limited fundamentally to around 2 T due to the number of Bohr magnetons per atomic site, and thus the magnetic moment achievable per atom). Furthermore, bulk superconductors also benefit from not requiring direct connection to a power supply, unlike electromagnets, and can be switched off safely by simply being warmed up. ...
... Firstly, the statistical nature of the failure mechanism means trapped fields of over 17 T could not be attained reliably, even for a batch of samples nominally fabricated identically. This was discussed by Durrell et al., where three sample stacks of similar composition and structure to the 17.6 T record stack were also magnetised under similar conditions at the same experimental facility [8]. The first stack suffered cracking and only trapped 10 T, the second successfully trapped 15.4 T, while the third also failed during magnetisation. ...
Thesis
Single-grain RE-Ba-Cu-O bulk high temperature superconductors [or (RE)BCO, where RE = rare earth element or yttrium] have demonstrated significant potential for practical applications due to their ability to trap magnetic fields in excess of 17 T, which is an order of magnitude greater than what can be achieved with conventional iron-based permanent magnets. One of the major obstacles to the use of (RE)BCO trapped field magnets is their poor mechanical properties, as bulk samples typically contain a large number of defects, such as pores and micro-cracks. Furthermore, significant electromagnetic stresses develop in bulk superconductors during magnetisation as a result of the Lorentz force, leading frequently to sample failure above around 10 T. Therefore, it is clear that the mechanical properties of bulk (RE)BCO need to be studied comprehensively and improved upon to realise the full potential of this technologically important material. This study first investigated the mechanical strength of YBCO single grains at room temperature by utilising three-point bend and Brazilian tests. This was followed by measurement of the mechanical deformation of GdBCO/Ag single grains in situ, i.e. during high-field magnetisation, to determine the strains and stresses experienced by the samples as a trapped field was established inside them at 64 K. Two techniques for improving the mechanical reliability of (RE)BCO bulk superconductors were subsequently developed. Firstly, samples of YBCO were melt-processed with artificial holes to reduce the defect population and to improve the intrinsic strength of the resultant single grains. As a result, the YBCO sample with artificial holes was able to survive significantly higher magnetisation fields and achieved a surface trapped field of 8.8 T at 30 K without any external reinforcement, which was not possible with the standard YBCO sample. Secondly, a composite structure was proposed, which involved reinforcing GdBCO/Ag single grains with stainless-steel sheets and shrink-fit stainless-steel rings. This preparation technique is also expected to improve the thermal stability of the overall structure. The first composite stack achieved 16.8 T and 17.6 T at 26 K and 22.5 K, respectively, in sequential magnetisation cycles, demonstrating the effectiveness of this reinforcement approach.
... Considering its significant potential in such properties [1][2][3][4][5] and mature fabrication technology of top-seeded melt-growth (TSMG) [5][6][7][8][9], the growth and application of single-domain REBa2Cu3O7−δ (RE123 or REBCO, RE = rare earth elements, such as Y, Gd, Sm and Nd) superconductors have been broadly and deeply investigated for decades [5,[10][11][12][13][14]. In TSMG process, one seed is placed on the sample surface to induce two types of growth sectors, a growth sector (a-GS) and c growth sector (c-GS). ...
... Equation (1)(2)(3)(4) and derive all the seed area and area ratios as listed in Table 3. It is evident that all types of seeding alignment have η values larger than 1, signifying the effect of ...
Article
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YBa2Cu3O7−δ (YBCO) bulk superconductors are regarded as the most promising alternatives for conventional permanent magnets as they provide high field trapping capacity at low temperatures. However, for further improving their superconducting properties, it remains a significant challenge to enlarge the c growth sector by large-sized seeds or multi-seeds while maintaining the microstructure with a low porosity or clean grain boundaries that enables their performance. Here, we report a novel seeding assembly approach by vertically-connecting strip-seeds for inducing potential [110]-oriented overgrowth. Initially, from naturally right-angled corners, YBCO rapidly crystallized to form kite-liked convex areas, which, together with the original seed, effectively functioned as a large-sized seed to generate a sizable c growth sector. The novel-seeded sample exhibited a promising structure not only free of grain boundaries, but also with a favorable porosity of 20.29%. Such a low value is similar to 19.77% of the small-seeded one and much lower than 34.20% of the large-seeded one. Finally, due to structure tailoring towards an enlarged c growth sector with maintained pore characteristics, high and mono-peak trapped fields of 16 mm diameter YBCO bulks were reliably attained, up to a record value of 0.7025 T. This work offers insights into design principles for boosting magnetic properties of other members in the YBCO family.
... For applications operating at liquid nitrogen temperature (77 K), YBCO is the material of choice due to its superior properties at elevated temperatures [15]. A record trapped field of 17.6 T at 26 K was reached in the literature, measured in between a stack of two melttextured YBCO bulk samples (25 mm diameter) [16], [17], closely followed by others employing differently processed bulks using infiltration growth (IG) [18] and stacks of YBCO tapes [19]. At 77 K, the trapped fields are typically around 0.4-0.5 T for a single pellet (20 mm diameter), and can reach up to 1 T when replacing Y by Gd or nonmagnetic Eu [20]. ...
... On the other hand, the PFM energizing places a size limit on the TF magnets as the coils must be able to produce a magnetic field being large enough to successfully replace the permanent magnets. YBCO bulk samples are prepared by melt-texturing [16], [17], [30] or the infiltration growth process, which provides a better control of the shape of the pellets [32]. However, obtaining large sample sizes is a difficult task as a good texture is essential to enable the flow of strong supercurrents [14]. ...
Article
Full-text available
Flux-Pinning Docking Interfaces (FPDI) in satellite systems were developed using bulk superconductors and permanent magnets in previous works. However, such FPDIs have limited magnetic field strength, consist of heavy-weight material, and can only be used with a single purpose, i.e., as chasing or docking satellite. Replacing the magnetic material in the FPDI by a trapped field (TF)-magnet would enable the interface to operate for both purposes, i.e., generating a (stronger) magnetic field and trapping it. We show the requirements for such a system and discuss the possible gains when using a TF-FPDI in satellites. To reduce the system weight, the use of superconducting foams as superconducting material is discussed in detail. Furthermore, the use of superconducting foams, the size of which can be easily upscaled, may also comprise the function of the damping material, so even more weight could be saved for the payload.
... REBa 2 Cu 3 O y (REBCO, RE: rare earth element) textured materials have been energetically developed owing to their high critical current density (J c ) under magnetic fields up to high temperatures, such as the temperature of liquid nitrogen, 77 K. Among them, REBCO melt-textured bulks have been widely studied especially for strong magnets using their high field-trapping (B T ) properties as high as ∼17 T, due to the large persistent current circulating in bulks [1][2][3]. Both the uniformity and reproducibility of B T distributions as well as high B T of REBCO bulks are essential for extensive applications. ...
... These values were comparable with ∼0.9 T at 77 K for the reported 24.15 mmϕ GdBCO bulk exhibiting the highest B T properties ever, i.e. B T >17 T at ∼30 K [3]. The quantitative evaluation of the degree of roundness will be discussed later in this paper. ...
Article
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.
... REBa2Cu3Oy (REBCO, RE: rare earth element) textured materials have been energetically developed owing to their high critical current density (Jc) under magnetic fields up to high temperatures, such as the temperature of liquid nitrogen, 77 K. Among them, REBCO melt-textured bulks have been widely studied especially for strong magnets using their high field-trapping (BT) properties as high as ~17 T, due to the large persistent current circulating in bulks [1][2][3]. Both the uniformity and reproducibility of BT distributions as well as high BT of REBCO bulks are essential for extensive applications. ...
... These values were comparable with the reported 24.15 mm GdBCO bulkexhibiting the highest BT properties ever, i.e. BT >17 T at ~30 K, showed BT,max of ~0.9 T at 77 K [3]. The quantitative evaluation of the degree of roundness will be discussed later in this paper. ...
Preprint
Full-text available
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 bulky crystal. 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.
... Single-grain, bulk high-temperature superconducting (HTS) materials have established potential to trap magnetic fields that are an order of magnitude greater than those achievable using conventional permanent magnets. HTS samples have trapped a record 17.6 T at 26 K [1] at the centre of two Agdoped GdBCO single grain superconductors 24 mm in diameter, and over 3 T at 77 K [2] on the surface of a 65mm GdBCO single grain bulk disc. As such, (RE)-Ba-Cu-O materials [(RE)BCO, where (RE) is a rare-earth metal or yttrium] are promising candidates for the generation of strong magnetic fields for use in several applications, including rotating electrical machines [3,4] magnetic separation [5] and drug delivery [6], when used as trapped field magnets (TFMs). ...
Article
When used as trapped field magnets (TFMs), single grain, bulk high-temperature superconducting (HTS) rings are promising candidates for the generation of strong, uniform magnetic fields for nuclear magnetic resonance (NMR). The pulsed field magnetisation (PFM) technique provides a low cost, compact and portable method to magnetise these samples as TFMs; however it has proven difficult to achieve high trapped fields in HTS rings using PFM. To date, a record field of only 0.60 T has been achieved for rings magnetised by single-pulse PFM – compared with over 4 T for disc-shaped HTS – and the reasons for this discrepancy are poorly understood. In this work, we use the finite element method (FEM) to model the propagation of magnetic flux into HTS rings under quasi-static zero field cooled (ZFC) magnetisation and PFM, and validate the results analytically and experimentally. Magnetic flux is found to penetrate finite HTS rings from both the inner and outer surfaces, inducing a negative field at the inner face of the ring. This field is reversed as the applied field increases past the point of full penetration, locally dissipating magnetic energy and heating the sample. HTS rings are therefore more susceptible to local instabilities that severely limit their ability to trap a useful magnetic field. Consequently, thermomagnetic stability of HTS rings during single-pulse PFM can only be ensured by taking careful consideration about reducing flux movement through the bulk around the point at which the field is reversed. This may require more advanced PFM techniques like waveform control or multi-pulse stepwise-cooling to reduce local heating and increase the trapped field.
... Therefore, the engineering critical current density, J e , is one of the important benchmark parameters for the superconducting wires consisting of superconductor, sheath material, metallic thermal stabilizer, and so on [1]. On the other hand, since the superconductor bulk independently acts as a trapped field magnet [2]- [4], the filling factor of bulk directly connects to the J e value which is basically the same as a critical current density, J c . An MgB 2 superconductor has some advantages such as a high critical temperature, T c , of 39 K [5] and no weak-link problem [6], [7], therefore the MgB 2 wires and bulks have been energetically studied by many researchers to equip for various practical applications [8]- [12]. ...
... Single crystal structure of Y-B-C-O or (RE)-B-C-O bulk high-temperature superconductors, where RE is a rare Earth element, These materials can generate large magnetic fields that are usually larger than those produced by traditional permanent magnets. As a result, there is a wide range of potential applications for this material [7], which includes flyers devices, such as trains, energy storage containers, and rotating machines. , Such as motors, generators and centrifuges [8][9][10]. ...
Article
Full-text available
The major problems that facing sustainability is the heat production with electricity transmission. The research and engineering communities hope that superconductive materials will be employed in the power transmission, without any losses along the way. Solid-state reaction is a one of the methods for preparing compound samples. This method was used to prepare the nominal chemical formula Y 2 Ba 4 Cu 7 O 15 . The calcining of the mixed powder at constant temperature of 800C0, followed by compressing the mixed, under (7, 8, 9) tons/cm2 pressures, as pallets shape with diameter 1.5 cm and thickness (0.2-0.3) cm inducing. The prepared samples were encounter many sintering processes through constant temperature. The sintering processes were done in the furnace by rising and cooling temperature with Oxygen rate 0.5 L/min. The samples were measured electrically to determine the resistivity changes in different temperatures (77–300) K, using four-probe technique. The results for the samples A, B and C shows the onset superconducting transition temperatures (Tc (onset)) at 88 K, 93 K, and 99 K respectively. The XRD data illustrated a polycrystalline structure for all samples. The transition temperature, oxygen content (δ) and the lattice parameter increase with increasing the pressure.
... Suzuki et al. reported that when the upper half of the DyBCO bulk superconductor is intercepted and stacked, the trapped field of the double-layer sample is twice that of the single layers [24]. The highest magnetic field of 17.6 T (26 K) was trapped by a stack of two Agdoped GdBCO bulk superconductors, according to Durrell et al. [25]. Huang to those of double-layer stacked bulks, discovering that the stacked bulks can provide a larger magnetic field in a wider area and over a longer distance than the single-layer sample at 50 K [27]. ...
Article
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The effect of the stacking height on the levitation force and trapped field properties of bulks was investigated using three groups of GdBa2Cu3O7−x (GdBCO) bulk superconductors with heights of 7, 5, and 3 mm. Each group contained four samples, and they were obtained by removing the bottom of the previous group of samples fabricated by the RE + 011 top-seeded infiltration growth method with similar properties. The four samples in each group were stacked in one, two, three, and four layers to form stacked samples with good uniformity and varying stacking heights. The levitation force and trapped field of the samples were measured, and results show that the levitation force and trapped field both increase initially and then tend to saturate as the stacking height increases. The variation of the levitation force is related to the decrease of induced current in the bottom layer with the increase in stacking height. While the saturation of the trapped field is caused by the increasing distance between the superconducting current in the bottom layer and the sample surface, which decreases its contribution to the trapped field. Additionally, the proposed method can produce the same magnetic field distribution at the top and bottom of the sample. It can optimize the properties and heights of REBCO (RE = Y, Gd, Sm, Nd, etc.) bulk superconductors, which is helpful to meet the practical application requirements.
... The superconductors are classified into two types with respect to temperature as high and low temperature superconductors. The high superconductor RE-Ba-Cu-O [(RE) BCO], where RE = Sm, Y, and Gd, have the ability to trap more magnetic fields than those produced by the permanent magnet field [1,2]. These materials will be important in high speed trains, medical, industrial, trapped flow devices, rotating electrical machines and energy storage systems [3][4][5]. ...
Article
Full-text available
The effect of partial substitution for lanthanum (La) on the structural properties of the compound Y 1-x La x Ba 4 Cu 7 O 15+δ was studied. The variation of (x) is x=0.1, 0.2, and 0.3, which was synthesized by the solid-state reaction method. The mixed powder was pressed with pressure (7 ton / cm2) as a disc (1.5 cm) diameter and a thickness of (0.25 to 0.3 cm). The samples were sintering at 120 °C / hour with a changing rate from room temperature to 850 ° C over 72 hours. XRD analysis using to calculate crystal size, strain, and degree of crystallinity. It was found all samples have orthorhombic structure and change of structure with increasing lanthanum concentration. It was shown that the change in lanthanum concentrations of all our samples produce a change in the crystal size, strain, degree of crystallinity, and lattice parameters.
... The bulk YBa2Cu3O7−δ (Y123 or YBCO) high-temperature superconductor has been preferentially considered for high-field permanent magnetic applications, such as superconducting maglev, magnetic bearings and cryomagnets [1][2][3][4], due to its excellent properties in critical current density, levitation force (LF, Fmax) and trapped magnetic field (TF, Bz max), as well as its mature preparation technology of top-seeded melt-growth (TSMG) [5][6][7][8]. As reported, a 26.5 mm diameter YBCO stack reached a TF of 17.24 T at 29 K [3] (recently, a 24.15 mm GdBa2Cu3O7−δ (GdBCO) stack trapped 17.6 T at 26 K [9]), representing the largest TF of YBCO superconductors so far at any temperature. This value is more than 10 times higher than the remnant field of the NdFeB permanent magnet. ...
Article
Full-text available
YBa2Cu3O7−δ (YBCO) single grain, as a pivotal and popular oxide ceramic, is of great importance in practical applications for its considerable potential in magnetic properties. Normally, sizable YBCO bulk superconductors are fabricated by multi-seeded melt-growth for time saving. However, the performance of such bulks has long suffered from certain methodological barriers related to artificially induced imperfect seeding, involving unreliable precision in seeding alignment and detrimental impact on grain boundaries. Here, a facile but effective in situ self-assembly (ISSA) strategy is reported for seeding structural design, in which exactly (110)/(110) aligned twin-seeds naturally arise through the self-replication of crystallographic orientation from one small seed during thermal procedure. Distinctively, after two induced grains impinging, a [110] oriented growth zone emerges and expands to the edge of the sample, leading to a contamination-free homo-combination. As a result, 25 mm diameter fully-grown bulks with single-grain quality were reliably attained, which exhibit superior levitation forces up to 65.1 N and field trapping capability up to 0.8943 T with a prominent feature of mono-peak. The ISSA seeding strategy in this work, with its nature in achieving exact seeding alignment, is widely applicable for the preparation of other high-performance bulks in the YBCO family.
... Single-grain REBa 2 Cu 3 O 7−δ superconducting bulks (REBCO or RE123, where RE denotes the rare-earth elements, such as Y, Gd, Nd, Sm and Eu, etc.) possess a high critical current density (J C ) and a great ability to trap magnetic flux (17.24 T at 29 K for YBCO [1] and 17.6 T at 26 K for GdBCO [2]), making them attractive for practical applications [3][4][5][6], such as magnetic levitation, axial-gap-type rotating machines, magnetic bearings and flywheels, etc. Compared with the conventional top-seeded melt texture growth (TSMG) method of fabricating singledomain REBCO bulks, the top seeded infiltration and growth (TSIG) process could overcome problems such as shape distortion, shrinkage of the final sample and leakage of the Ba 3 Cu 5 O 8 liquid phase, etc. [7][8][9][10][11]. ...
Article
Full-text available
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 superconductors are classified into two types with respect to temperature as high and low temperature superconductors. The high superconductor RE-Ba-Cu-O [(RE) BCO], where RE = Sm, Y, and Gd, have the ability to trap more magnetic fields than those produced by the permanent magnet field [1,2]. These materials will be important in high speed trains, medical, industrial, trapped flow devices, rotating electrical machines and energy storage systems [3][4][5]. ...
Article
The eff ect of partial substitution for lanthanum (La) on the structural properties of the compound Y1-xLaxBa4Cu7O15+δ were studied. The variation of (x) are x=0.1, 0.2 and 0.3, which was synthesized by solid state reaction method. The mixed powder was pressed with pressure (7 ton / cm2) as a disc (1.5 cm) diameter and a thickness of (0.25 to 0.3 cm). The samples were sintering by 120 °C / hour with a changing rate from room temperature to 850 ° C through 72 hours. XRD analysis using to calculate crystal size, strain and degree of crystallinity. It was found all samples have orthorhombic structure and change of structure with increasing lanthanum concentration. It was shown that the change lanthanum concentrations of all our samples produce a change in the crystal size, strain, degree of crystallinity and lattice parameters.
... The non-dissipative transport of currents at temperatures of 77 K makes the hightemperature superconductors (HTS) fascinating materials for the development of novel devices and their applications at high magnetic fields and in storage energy [1][2][3][4][5][6][7][8][9][10][11][12][13]. A large number of those applications consists in the production of HTS films which has been reported to be prepared by sputtering [14,15], PLD [16], and MOCVD [17] techniques. ...
Article
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The production cost is one of the issues for some complex ceramics applications, like the superconducting oxides. The main properties of such materials, i.e., zero electrical resistivity and perfect diamagnetism, make them attractive for several applications, including energy storage. Thus, in this work, we focus on the production and structural characterization of BSCCO superconducting films using a domestic inkjet printer. The precursor solution was prepared following Pechini's method, and it was used, such as the ink. Then, an E-shape film was printed over a SiO2 substrate. The results show that the sample produced with 12 depositions presented a superconducting transition at 81 K and a critical current density of 9.68 A/cm2 at 78 K.
... S UPERCONDUCTING bulk materials single-grain RE-BaCuO, where RE denotes rare-earth elements or yttrium, are promising for the high performance magnets that can trap large magnetic field in compact space [1], [2]. REBaCuO bulk materials are subjected to electromagnetic force and thermal stress during the magnetization process [3]- [7]. ...
... These applications lie on the excellent flux trapping performance and unique self-stable levitation ability of bulk HTS superconductors. It has been reported that a bulk superconductor can trap a magnetic field of greater than 17 T at 30 K [1,6,7] and 3 T at 77 K [8]. ...
Article
Zn doping which may induce a second peak effect in YBa2Cu3O7−δ (YBCO) has been opted as a regular routine to improve the trapped field and flux pinning stability of YBCO bulk superconductors for practical applications such as quasi-permanent or maglev magnets. Here, the effects of Zn doping on the flux trapping performance of single domain YBCO bulk superconductors have been systematically investigated.The doping amount xvaries from 0 to 1.0 mol%. We analyzed the critical transition temperature (Tc), critical current density (Jc), trapped field (Bt) and the flux relaxation at various temperatures, and measured in addition the levitation force (FL) for comparison.The doping amount of 0.6 mol% has been proved to be the optimal value which enhances self-field Jc by a factor of 11 at 30 K with an obvious secondary peak effect, resulting in great improvements in trapped field and flux stability. The holistic and local superconducting performances exhibit good agreements demonstrating Zn-doping an effective method to improve flux pinning properties for practical applications.
... As shown in [137], state-of-the-art IBS tape processed with hot-pressing obtained a J e of 300 A mm −2 at 4.2 K and 10 T, but there is still large room for being advanced [138]. In 2014, Durrell et al trapped a record field 17.6 T at 26 K in silver doped, melt-processed GdBCO bulks [139]. The GdBCO bulk is silver doped for enhancing its mechanical performance and pre-stressed by a shrink-fitted stainless steel for avoiding a premature quench. ...
Article
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Superconducting undulators (SCUs) with period >15 mm can offer much higher on-axis undulator field B0 than state-of-the-art cryogenic permanent magnet undulators (CPMUs) with the same period and vacuum gap. The commissioned NbTi planar SCUs for user operation in the Karlsruhe Institute of Technology (KIT) synchrotron and the Advanced Photon Source (APS) storage ring are operated stably without quenches, producing outperformed photon flux in the high energy part of the hard X-ray spectrum. Another potential advantage of deploying SCU is its radiation hardness, a crucial characteristic for being used in free electron lasers (FELs) driven by high repetition rate superconducting linear accelerators (LINACs) and diffraction limited storage rings (DLSRs) with small vacuum gap and large averaged beam current. Development of shorter period but high field SCU is an important mission in an EU founded CompactLight project as this technology would reduce both the length of undulators and the length of LINACs. This review paper first overviews the research and development of SCUs worldwide from late 1970s to 2021, then presents the SCU design requirements and compares the theory limits of different types of planar and helical SCUs, and finally reviews the technical challenges including the SCU cryostat, the magnetic field measurement, the integral/local field correction and the high-temperature superconductor (HTS) challenges and prospects the research needs for SCUs.
... In the Meissner phase, the magnetic field of the region is zero [11]. In the normal phase, the magnetic field is proportional to the external magnetic field, the constant of proportionality being determined from the magnetic permeability of the sample in its normal state [12]. Finally, in the vortex phase, the magnetization of the sample decays from a constant value to zero as the vortices shrink in size. ...
Preprint
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Vanadium is an elemental type-II superconductor which has a pure superconducting phase, a vortex phase, and a non-superconducting phase. We designed and carried out a low-budget experiment in our undergraduate physics lab to measure the magnetic field a close distance from the surface of a pure Vanadium disk sample isothermally with a Hall sensor across a range of different temperatures and external magnetic fields. We then used these measurements to compute the superconducting phase diagram of Vanadium. After completing measurements at eight temperatures ranging from 2.6K to 5K and magnetic fields ranging from -0.2T to 0.2T, we were able to detect the Meissner phase (clearly), and a vortex phase (less clearly). Using the graphs of the hall bar magnetic field versus external magnetic field, we were able to derive a rough estimate for the upper critical field and the lower critical field of Vanadium at the eight temperatures wherein we conducted measurements. The results are in general accord with the phase diagram of Vanadium found in the literature, except that the critical temperature appears to be less than 5.43K and 5.13K (about 4.8K). Further, we observed critical fields lower than those found in the literature. We hypothesize this is due mostly to impurities in our Vanadium sample (purchased through Amazon.com), which would reduce the measured critical temperature below that of pure Vanadium, consistent with our results.
... The world record of trapped magnetic field in stacks of REBCO superconducting layers is 17.7 T [81], which slightly outperform bulk superconductors. A field of up to 17.6 T magnetic field at 26K in a stack of two silver-doped GdBCO SC-bulks has also been trapped [82]. These are much higher trapped fields than those for conventional permanent magnets, being up to 3 T only. ...
Thesis
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High Temperature Superconducting stacks and bulks can be used in the rotors of the motors of hybrid-electric aircraft propulsion, which can reduce the greenhouse emissions in aviation industry. Though, on application of cross magnetic fields present inside such motors, these superconducting magnets can demagnetize rapidly. Also, the superconductors are vulnerable to Electro-thermal quench due to large screening currents and high voltages, for applications such as high field magnets and motors. There is a need for a fast and accurate numerical software to analyze these problems. In this thesis work, we have developed a numerical model using variational principles that can calculate demagnetization for millions of cycles for very thick stacks (up to 100 tapes) in relatively short time (orders of magnitude faster than the commercial software). For high number of ripple field cycles, we have observed that the trapped field reaches a permanent non-zero asymptotic value for HTS stacks, if the ripple field amplitude is lower than the tape’s parallel penetration field. We have also developed a coupled Electro-magneto-thermal software, which uses variational principles, to accurately simulate the quench behavior of superconductors. As coded in C++ in-house, this software is very fast and highly customizable. The models developed during this thesis work can be used for a quick and complete Electro-Magnetic and Electro-Thermal analysis of practical large scale superconducting applications such as high field magnets, fault current limiters, motors, and generators, by engineers and scientists.
Article
We have successfully trapped a field of 17.89 T at 6.5 K at the center of a compact coated-conductor (CC) stacks (13×12×11.7 mm ³ ) within 75 min by suppressing flux jumps. The CC stack consists of 200 sheets of EuBa 2 Cu 3 O 7 CCs with BaHfO 3 nanorods to increase the critical current density at high fields and low temperatures. To enhance thermomagnetic stability, the central 50 CCs are coated with 1 µm thick Pb with large specific heat at low temperatures. Numerical calculations based on the actual J c - H characteristics reproduces the trapped field quantitatively. New directions for achieving even higher trapped field at higher temperatures and making use of the trapped field are discussed.
Article
A quantum nature of vacuum is expected to affect electromagnetic fields in vacuum as a nonlinear correction, yielding nonlinear Maxwell's equations. We extend the finite-difference time-domain (FDTD) method in the case that the nonlinear electromagnetic Lagrangian is quartic with respect to the electric field and magnetic flux density. With this extension, the nonlinear Maxwell's equations can be numerically solved without making any assumptions on the electromagnetic field. We demonstrate examples of self-modulations of nonlinear electromagnetic waves in a one-dimensional cavity, in particular, in a timescale beyond an applicable range of linear approximation. A momentarily small nonlinear correction can accumulate and a comparably large self-modulation can be achieved in a long timescale even though the electromagnetic field is not extremely strong. Further, we analytically approximate the nonlinear electromagnetic waves in the cavity and clarify the characteristics, for example, how an external magnetic flux density changes the self-modulations of phase and polarization.
Article
The so-called ring-shape superconducting trapped field magnet has great potential for commercial application due to its flexible size and joint-less structure. However, due to the spatial asymmetry of the structure, the trapped magnetic field has a non-negligible magnetic declination, which becomes the major obstacle to its application. To compensate the magnetic declination, a new concept of superconducting hybrid magnet consisting of the ring-shape magnet and the HTS bulk is proposed. By adjusting the placement of the HTS bulk in the central air gap, magnetic declination can be effectively compensated. Both experiments and 3D numerical model are used to evaluate the magnetic uniformity after compensation. The results show that the proposed hybrid magnet will have an obvious compensation effect on the magnetic declination. And the hybrid magnets have promising applications with requirements on the uniformity of magnetic field such as potable MRI.
Article
A high-temperature superconducting (HTS) motor has been developed using bulk superconductors as quasi-cryo-permanent magnets to allow a stronger remanent field. In this work, we focus on the in-situ magnetization of the bulk superconductors which is considered one of the main challenges. YBa<sub>2</sub>Cu<sub>3</sub>O<sub>7-</sub> bulks that had been used in the motor were magnetized via pulsed field magnetization (PFM) as single samples and assembly. The peak trapped field achieved via PFM is similar to that achieved via field cooling magnetization at 77 K. For the bulk assembly, the existence of a neighboring bulk superconductor was found to affect the penetration of the magnetic flux during the PFM process especially under low applied fields. This leads to a 3% to 4% reduction in peak trapped field, and 10% to 13% reduction in integrated magnetic flux.
Thesis
Full-text available
Superconductor technology has attracted increasing attention during the last few years because of their advancements made in the material manufacturing technology and the reduction of cost. As a result, superconducting materials have been widely applied to power industries, of which one of the most promising and popular applications is the electric machine, which is the core component of power generation and consumption on the earth. The second-generation (2G) high temperature superconducting (HTS) coated conductor (CC) has become increasingly appealing among all the superconductors on account of its commercial availability and advantageous current carrying capacity. Therefore, HTS electric machines are believed to usher in a period of development opportunities. However, there still exist many challenges related to the efficiency, cost-effectiveness, reliability, and safety of HTS machines, and the alternating current (AC) loss of HTS CCs remains one of the most significant issues. Over the years, the effort of studying the AC loss of HTS CCs has yielded many outstanding research outcomes; however, most of them have been focused on the loss estimation at power frequencies under purely sinusoidal currents and magnetic fields. In fact, the electromagnetic environment in electric machines is abundant in high-frequency ripple fields and harmonics, especially for high-speed rotating machines. Therefore, the AC loss characteristics of HTS CCs at high frequencies remain unclear, to some extent. Aiming to analyse systematically the AC loss properties of HTS CCs applied to electrical machines within a wide frequency band, from the power frequency to kHz level, this thesis adopts analytical equations, numerical modelling methods, as well as experimental measurements. In doing so, this project hopes to contribute to the loss quantification and controlling of HTS CCs in electrical machines, providing a useful reference for the design of large-scale superconducting devices. This thesis starts by providing a comprehensive literature review of the state of the art of AC loss related studies. The analytical formulae, modelling methods, measurement approaches, as well as reduction techniques for the AC loss of HTS materials in both low- and high-frequency fields are systematically summed up. The review work clarifies the research status of the AC loss of superconducting materials applied to electric machines, elucidating that the electromagnetic loss characteristics of HTS CCs deserve further investigation, especially at high frequencies in high-speed rotating machines. Numerical models are an indispensable tool for studying the anisotropic electromagnetic properties of high temperature superconductors (HTSCs), thus numerical modelling is chosen as a primary method in this thesis to study the AC loss of HTS CCs employed in electric machines. The methodologies adopted to build the simulation models are introduced, which are based on Maxwell’s equations and the finite element method (FEM). The numerical models here are developed mainly through two formulations, namely T-formulation (T represents current vector potential) and H-formulation (H denotes magnetic field), which can be achieved by FORTRAN 90 or incorporated into COMSOL Multiphysics. Dynamic loss is a crucial component of the AC loss of HTS field windings in superconducting machines, which occurs when the HTS CC carrying a direct current (DC) is exposed to an AC magnetic field. Therefore, the dynamic loss of HTS CCs is explored in detail. The dependence of dynamic loss on the material properties (critical current density and n-value) is investigated. Then, a novel formulation is derived to describe the full-range variation of dynamic loss. At last, three new parameters are defined to characterise the non-linearity of dynamic resistance. The proposed analytical formulae and parameters are validated by the T-formulation based numerical model and experimental measurements. In superconducting machines, the HTS CCs are usually utilized in the form of stacks and coils. Therefore, besides a single HTS CC, the transport current loss, magnetization loss, dynamic loss, and the total AC loss of HTS stacks, coils (circular and racetrack coils), and trapped field stacks (TFSs) over a wide frequency band, from the power frequency to kHz level, are studied respectively. The H-formulation based 2D and 3D numerical models are mainly adopted here, which are validated by published experimental data. It is found that the widely used thin film approximation in modelling which only considers the superconducting layer of HTS CCs is inapplicable at high frequencies (higher than 100 Hz for magnetization loss) due to the skin effect, and the non-superconducting parts (the copper stabilizer, silver overlayer, and substrate) have to be taken into account. AC loss varies non-linearly with the frequency of the AC transport current or magnetic field because of the electromagnetic interactions between different layers. The shielding effect between different turns of an HTS coil is also explored, which can enhance the dynamic loss in the middle turns of the coil while the magnetization loss occupies the majority in the outer turns at high frequencies. The electromagnetic properties of a curved HTS TFS under high-frequency cross fields are investigated, too, which possesses geometrical applicability for cylindrical rotating shafts. It is demonstrated that the widely adopted 2D-axisymmetric models are inapplicable to study the anisotropic electromagnetic distributions of TFSs because of the emergence of the electromagnetic criss-cross. High-frequency ripple fields can drive induced current towards the periphery of the HTS TFS due to the skin effect, leading to a fast rise of AC loss and even an irreversible demagnetization of the TFS. In order to combine AC loss analysis and machine applications, a special magnet made of HTS coils in the form of a Halbach array is exploited in the designs of an air-cored wind turbine generator and an electrodynamic wheel (EDW) used for maglev, through numerical modelling in COMSOL Multiphysics. The HTS Halbach Array magnet (HAM) can focus the magnetic flux inside the coil loop, greatly increasing the magnetic flux density in the airgap and the power density of the machine. The HTS HAM represents a generic topology/approach for the design of fully air-cored superconducting machines. The proposed HTS HAM EDW can generate higher thrust and lift forces, and greatly reduce the weight of the magnets compared with the conventional design with permanent magnets (PMs), opening the way to future on-road maglev vehicles. It is also illustrated that, for modelling the electro-mechanical performance of large-scale HTS devices, e.g., synchronous electric machines, the HTS field coils can be reasonably equivalized as conventional ones carrying the same DC so that the computation complexity can be largely decreased. This thesis starts with the application of superconductors to electric machines, analyses thoroughly the loss characteristics of HTS CCs, stacks, coils, and TFSs over a wide frequency band from the power frequency to kHz level. It is believed that this research work can help researchers in the communities of applied superconductivity and electrical machines better understand the electromagnetic properties of different HTS topologies, provide a useful reference for the quantification and controlling of AC loss, and thus give a significant guideline for the design of high power density superconducting machines.
Article
Bulk high temperature superconductors based on the rare-earth copper oxides can be used effectively as trapped field magnets capable of generating large magnetic fields. The top-seeded infiltration growth (TSIG) processing technique can provide a more homogeneous microstructure and therefore more uniform superconducting properties than samples grown using conventional melt growth processes. In the present investigation, the properties of bulk, single grain superconductors processed by TSIG and magnetised by the pulsed-field magnetisation technique using a copper-wound solenoid have been studied. A trapped field of ∼3 T has been achieved in a 2-step buffer-assisted TSIG-processed Y-Ba-Cu-O (YBCO) sample at 40 K by magnetising the bulk superconductor completely via a single-pulse magnetisation process. Samples were also subjected to pulsed-field magnetisation at 65 K and by conventional field-cooled magnetisation at 77 K for comparison. Good correlation was observed between the microstructures, critical current densities and trapped field performance of bulk samples fabricated by TSIG and magnetised by pulsed-field and field-cooled magnetisation. The homogeneous distribution of Y 2 BaCuO 5 inclusions within the microstructure of bulk YBCO samples fabricated by the 2-step buffer-assisted TSIG process reduces inhomogeneous flux penetration into the interior of the sample. This, in turn, results in a lower temperature rise of the bulk superconductor during the pulsed-field magnetisation process and a more effective and reliable magnetisation process.
Chapter
GdBa2Ca3Cu4O10.5+δ superconducting perovskite nanomaterial is prepared by subsequent steps viz. weighing, mechanical mixing, ball milling, attrition milling and calcination, and applying solid state reaction technique. By XRD studies of GdBa2Ca3Cu4O10.5+δ/GBCCO nanosystems (prepared at various calcination temperatures—30, 500, 850, and 900°C) crystallinity of the samples are confirmed. Using XRD results and applying XPERT PRO software, the lattice parameters and orthorhombic crystal system of the ceramic sample are analyzed. Structural parameters such as d spacing, dislocation density and number of particles per unit surface area are determined as functions of calcination temperature for preferred high intensity peaks (110), (111), (321), and (521). Particle size of preferred orientations at various calcination temperatures are obtained by XRD diffraction peak profile analysis methods such as Debye Scherrer's formula, Cauchy equation, and Williamson Hall (WH) plot method and nanostructure property is confirmed. WH plot also yields the values of lattice strain. It is observed that calcination temperature affects structural parameters.
Article
We have studied the trapped field properties of the MgB2 bulk superconductors fabricated by various methods. The MgB2 bulks were magnetized by a filed-cooled magnetization (FCM) method using a superconductor coil and a pulsed field magnetization (PFM) method using a copper coil. We firstly obtained a trapped field of 1.5 T at 14 K by FCM for an MgB2 disc bulk (30 mm diameter and 7 mm thickness) with a filling factor of about 50 %, which was fabricated by an in-situ capsule method using a home-made capsule. The trapped field of MgB2 bulk by FCM was enhanced up to 2.9 T by the densification and the enlargement. Such dense MgB2 bulks were fabricated by an in-situ hot isostatic pressing under the pressure of up to 980 MPa or an ex-situ spark plasma sintering by applying uniaxial stress of 50 MPa. An in-situ infiltration method without the physical pressure also produced the dense MgB2 bulks, which trapped a 3 T-class magnetic field. The Ti-doping improved considerably the trapped field by FCM up to 5.6 T at 11.3 K for the triple-stacked Ti-doped MgB2 bulks. The PFM method also produced a Tesla-class MgB2 bulk magnet. The trapped field of 1.1 T at 13 K was obtained for the HIP-processed MgB2 disc bulk (22 mm diameter and 20 mm thickness). A magnetic field of 1.6 T was trapped at 20 K in the MgB2 bulk composite, consisting of two ring-shaped MgB2 bulks sandwiched by four thin copper plates and an inserted soft-iron yoke cylinder, using double PFM using a split-type coil with softiron yokes. We have shown the potential of the MgB2 bulk magnets for the practical superconducting applications.
Article
During quasi-static magnetization of bulk superconductors using field-cooled magnetization (FCM) from high fields at low temperatures, such bulks are sometimes broken, which is believed to be mainly due to an electromagnetic force – and subsequent stress – larger than the fracture strength. However, a ring bulk can break, even during pulsed field magnetization (PFM), from relatively lower pulsed fields and at relatively higher temperatures. Previous simulation results suggest that the ring bulk should not break due to the electromagnetic force during PFM. In this paper, taking experimental and numerical results into consideration, we propose the possibility of mechanical fracture of a ring bulk during PFM due to thermal stress induced by local heat generation, which has not been considered and investigated to date. Two numerical models with different sizes of heat-generating region were constructed for the ring bulk with a relatively large inner diameter (60 mm outer diameter, 36 mm inner diameter, 17 mm height). For Model-1, with a large heat region, the bulk fracture due to the thermal stress results from the tensile stress along the radial direction in the neighboring heat region. The risk of bulk fracture is enhanced at the inner or outer edges of the bulk surface, compared with that inside the bulk. For Model-2, with a small heat region inside the bulk, the bulk fracture due to the thermal stress results from the compressive stress along the radial direction in the neighboring heat region. These results strongly suggest the possibility of mechanical fracture of an actual ring bulk due to thermal stress induced by local heat generation. This idea is also applicable more generally to the fracture mechanism during FCM of superconducting bulks.
Article
Pulsed magnetization of superconducting bulks is attractive for promoting the use of superconducting technology in various commercial applications. Several researchers have been developing new magnetizing techniques to improve the trapped magnetic field obtained with pulsed magnetization. Waveform control pulsed magnetization (WCPM) is one of these new magnetizing techniques. The WCPM has been developed for a few years in our laboratory and has shown promising results so far. In this presentation, a numerical simulation of the magnetization technique has been performed with the aim of better understanding and improving the WCPM. The experimental set-up, consisting of one (RE)Ba2C3O7- (REBCO, RE = rare earth) bulk sandwiched in between two vortex type coils similar to the internal configuration of an axial-gap type superconducting rotating machine has been modelled in COMSOL Multiphysics. A coupled H-A field formulation has been implemented so that the regions containing the superconductor are solved using the magnetic field H and the surrounding regions, containing the vortex-type coils are solved using the magnetic vector potential A. A thermal model has been added to consider the rise of temperature in the bulk during the magnetization. The coils are connected through a circuit interface, in which the circuit of our pulsed magnetization system has been implemented. The trapped magnetic flux density obtained using a simple pulsed field magnetization is compared by the trapped magnetic flux density obtained with WCPM using negative feedback. The important parameters are discussed as well as the impact of this technique on the heat generation in the bulk during the magnetization.
Article
In this paper, we use the magnetic field and displacement distributions to detect crack in bulk superconductors. The (Re)BCO bulk superconductors are ceramic oxides which have low mechanical strength. During the field cooling magnetization, the large Lorentz force will be generated in bulk superconductor, which will cause stress concentration near the cracks. When the local stress exceeds the fracture toughness, cracks will propagate and even cause damage of the bulk. In order to ensure reliability of bulk superconductor, it is necessary to determine location and size of crack. For bulk superconductor with a crack, the crack can also affect the magnetic field distribution. Firstly, we combine the Genetic Algorithm (GA) and magnetic field to detect crack in bulk superconductor. The values of position and shape information of crack in bulk superconductor can be obtained with objective function. After that, we obtain the electromagnetic force based on the magnetic field distribution. The Extend Finite Element Method (XFEM) with electromagnetic force is used to calculate the displacement of the bulk superconductor with a crack. The displacement and GA are also used to detect crack in bulk superconductor. Finally, we present a comparison between the magnetic field detection and the displacement detection. For horizontal crack, the displacement detection is more effective than the magnetic field detection.
Article
We report a new methodology in bulk MgB 2 ring production for use in small-scale magnetic shielding or bench-top NMR systems. This process is a modified field-assisted sintering technique (mFAST) which enables direct formation of the rings without the need for machining or additives into the precursor powder. The shielding and trapped field capabilities of three mFAST MgB 2 rings were determined using zero-field- (ZFC) and field-cooled (FC) magnetic experiments. Individual bulks trap magnetic fields up to 1.24T at 20K comparable to the highest published data for a ring sample. It is anticipated that for many applications, multiple rings will be stacked to form the required experimental structure. We find for the three ring stack a trapped field of 2.04T and a maximum shielded field of 1.74T at 20K. The major factor limiting performance at low temperatures are flux jumps which cause rapid loss of the trapped field or shielding capability. Preliminary studies of magnetic field ramp rate dependence on flux jumps were conducted illustrating that even at very slow ramp rates (0.007 T/min) they remain a significant issue. Despite this concern, we conclude that mFAST represents an exciting new fabrication methodology for bulk MgB 2 rings.
Article
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 REBa2Cu3O7–δ (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.
Article
Full-text available
The enhancement of a critical current density ( J c ) of REBa 2 Cu 3 O 7- δ (REBCO/YBCO, where RE=rare earth elements and Y) bulk superconductors can be achieved via dispersing normal-conductive RE 2 BaCuO 5 (Y211) particles and other defects which are of nano-metric size in the superconducting matrix. Recently, we demonstrated the integration of high-energy ultrasonic irradiation for fabricating high quality YBCO superconductors which effectively improved J c and trapped fields. In the present work, we investigated the effect of 30 mol.% of Y211 particle produced via high-energy ultrasonication irradiation on the growth and superconducting properties of top-seeded melt grown bulk YBCO single grains. Ultrasonic power of 450 W was employed for 30 minutes to create the sharp-edged, individual and nano-meter sized Y211 phase particles. Systematic isothermal experiments were conducted at various temperatures from 1005 °C − 980 °C. The growth of YBCO grain from a single crystalline NdBCO seed was initiated at 1000 °C and as the isothermal temperature decreased the growth area increased due to the improved peritectic reaction. The field dependence of J c was improved when the under-cooling isothermal temperature decreased. The present method is reliable, cost-effective, and free from any chemical contamination.
Article
Full-text available
We report on top-seeded melt growth of GdBa 2 Cu 3 O 7- δ (GdBCO) bulks added by sharp edged Gd 2 BaCuO 5 nanoparticles (Gd211 U ) refined by ultrasonication. GdBCO bulks mixed with 30 mol.% of Gd211U were examined to be grown isothermally at different temperatures in a range of 1015 °C−1035 °C using a top-seeded melt growth technique. Magnetic susceptibility measurements show that all samples become superconducting and especially samples grown at 1020°C and 1025°C have a maximum superconducting transition temperature ( T c ) of 94.5 K. The critical current density ( J c ) obtained from magnetic hysteresis loops for magnetic fields parallel to the c -axis is up to 65100 A/cm ² (the self-field at 77 K) for a sample grown at 1025 °C, while J c of a GdBCO bulk with conventional Gd211 particles grown at 1025 °C for comparison is 29000 A/cm ² (the self-field at 77 K).
Article
Bulk, single grain RE-Ba-Cu-O [(RE)BCO] high temperature superconductors (HTS) could potentially be used to generate stable magnetic fields for MRI and NMR. In these applications, however, the homogeneity of the magnetic field is of critical importance. As a result, the spatial distribution of critical current density, Jc, within the bulk single grain and the effects of the magnetisation process, which are primary drivers of the uniformity of the achievable trapped magnetic field, are fundamental to assessing the performance of these technologically important materials. This paper reports the systematic measurement of the distribution of Jc-B at 77 K over a vertical cross-section of a single grain along a facet line and through the seed crystal [(110)-F] at 20 positions within a 20 mm-diameter Gd-Ba-Cu-O sample in an attempt to understand and assess the distribution of Jc along this microstructural feature. A comparison of the data within the whole vertical plane across the seed measured along the a or b direction within the [(100)-a] plane shows that Jc-B at 77 K at the facet line is more than 10% higher for applied fields between 0.2 T to 2.5 T. The effect of the Jc-B relationship of the facet line on the overall trapped field measured in an individual bulk sample was investigated by measuring the magnitudes of trapped fields and their contour maps for sections cut from four single grain samples of GdBCO-Ag at different sizes and shapes parallel to the ab-plane from the top to the bottom of the bulk sample. Based on the results reported here, we demonstrate a method to achieve more uniform trapped fields through an optimal arrangement of an assembly of sections of individual GdBCO single grains.
Article
This review paper summarizes and analyses the current literature on the synthesis of dense MgB2 bulk with high density and by both the modified solid reaction method and the Mg infiltration method. MgB2 bulk shows Telsa-level magnetic field-trapping ability in small volumes (1-5 cm³) at 15-20 K, which is beneficial for multiple applications, particularly where light weighting is beneficial. The review also compares the properties of MgB2 to rare earth barium cuprate bulk magnets and NbTi solenoid magnets and discuess potential applications such as magnetic lenses, compact NMR, and magnetic shielding.
Article
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 systems.
Article
Full-text available
The development of superconducting technology has seen continuously increasing interest, especially in the area of clean power systems and electrification of transport with low CO2 emission. Electric machines, as the major producer and consumer of the global electrical energy, have played a critical role in achieving zero carbon emission. The superior current carrying capacity of superconductors with zero DC loss opens the way to the next-generation electric machines characterized by much higher efficiency and power density compared to conventional machines. The persistent current mode is the optimal working condition for a superconducting magnet, and thus the energization of superconducting field windings has become a crucial challenge to be tackled, to which high temperature superconducting (HTS) flux pumps have been proposed as a promising solution. An HTS flux pump enables current injection into a closed superconducting coil wirelessly and provides continuous compensation to offset current decay, avoiding excessive cryogenic losses and sophisticated power electronics facilities. Despite many publications regarding the design and analyses of various types of HTS flux pumps, the practical application of HTS flux pumps in a high-performance superconducting machine has been rarely reported. Therefore, it is of significance to specify the main challenges for building and implementing a reliable HTS flux pump. In addition, the physical mechanisms of distinct HTS flux pumps have caused some confusion, which should be clarified. Above all, a systematic review of the recent development and progress of HTS flux pumps remains lacking. Given the above-mentioned issues, this paper summarized the most up-to-date advances of this emerging technology, clarified the working mechanisms and commonly adopted modeling approaches, presented objective analyses of the applicability of various HTS flux pumps, specified the primary challenges for implementing HTS flux pumps, and proposed useful suggestions to improve this wireless excitation technology. The overall aim of this work is to bring a deep insight into the understanding of HTS flux pumps and provide comprehensive guidance for their future research and applications.
Article
Recently, the improvement of flux pinning performance of REBa2Cu3O7-δ (REBCO) bulk was achieved employing high energy ultrasonic irradiation (up to 300 W and 60 min) prior to the infiltration-growth process. Here, we demonstrate that higher ultrasonic power and shorter duration treatment (450 W for 30 min) of the RE2BaCuO5 (RE211, RE = Y, Gd) powder produces individual, nanometer-sized and surface damaged ultrasonically pre-treated RE211 particles (RE211Ultra). We study the growth of YBCO and GdBCO systems via top-seeded melt-growth (TSMG) method and with the addition of 30 mol% of RE211Ultra, which were pre-treated by high-energy ultrasonication and compared with the conventional method. Isothermal growth experiments clarified that the addition of RE211Ultra particles enables faster and more effective crystal growth via an improved peritectic reaction due to their size in the nanometer range and due to the presences of sharp edges, which is crucial for growing large, single grain bulks of REBCO. Microstructural investigations by scanning electron microscopy indicated the presence of 2 differently sized RE211 inclusions within the bulk GdBCO and YBCO superconductors. All samples showed an onset of superconductivity at ~92 K or above. Utilizing the effective growth temperature window and the addition of RE211Ultra, single grain bulks of GdBCO and YBCO were fabricated by the slow-cooling method. The field dependence critical current density (Jc) of the bulk samples using RE211Ultra were found to exhibit superior performance over the standard GdBCO/ YBCO samples due to significant changes of sample growth and of their microstructures. Here, we discuss various factors affecting the addition of RE211Ultra on the development of the microstructure, the growth of bulk, single grain materials and further, the superconducting properties of different REBCO superconductors.
Chapter
This chapter focuses on two important aspects of advancing and engineering rare-earth, cuprate-based bulk high-temperature superconductors [(RE)BCO] for both established and more innovative applications of these technologically important materials. This chapter presents a brief review of recent advances in processing, including the reliability of single grain growth, enhancement in the superconducting properties of melt-grown and infiltration-grown (RE)BCO bulk materials, achieved via engineering of the sample microstructure. Subsequently, the design of single grain (RE)BCO bulk superconductors for a range of novel applications, including hybrid trapped field magnetic lensing, high-performance magnetic shields, large-gradient magnetic separation and bench-top NMR/MRI ring-shaped stacks will be discussed. The second part of the chapter focuses on the applications where large electromagnetic stresses are characteristically a limiting factor. In this context, the in-situ and ex-situ reinforcement strategies explored in the (RE)BCO bulk framework to transform these ceramic-like materials into more robust, high performance bulk superconductors is reviewed and summarized. In-situ reinforcement strategies such as the addition of Ag, introducing thin-wall artificial holes in bulk samples during processing and the integration of fibres into the bulk (RE)BCO microstructure and ex-situ reinforcement strategies such as composite stacking comprising of laminated (RE)BCO bulk discs sandwiched between layers of stainless-steel plates and pre-stressing the bulk single grains with stainless-steel rings via a shrink-fit approach will be discussed and reviewed. Overall, therefore, this chapter will address the advances made in bringing single grain (RE)BCO bulk superconductors closer to deployment in both established and more innovative and challenging applications.
Article
In applications requiring a large magnetic force, permanent magnets with non-parallel magnetization directions can be assembled in a Halbach array to generate a large gradient of magnetic flux density. The saturation magnetization of permanent magnets, however, brings a fundamental limit on the performance of this configuration. In the present work, we investigate experimentally the assembly of cuboid bulk, large grain melt-textured YBa 2 Cu 3 O 7−x superconductors (∼14×14×14 mm ³ ) with orthogonal c-axes so as to form a basic unit of Halbach array. The experiments are carried out at 77 K. The experimental distribution of the magnetic flux density above the array of trapped-field superconductors is compared to a similar array made of permanent magnets. A simple analytical model is developed and is shown to accurately reproduce the main experimental observations. The results suggest that a redistribution occurs in the current flowing in the central sample when the distance between the superconductors is reduced, whereas the neighbouring superconductors are unaffected. It is shown that this current redistribution yields a reduced contribution of the central sample to the magnetic flux density above the centre of the array and a new negative contribution associated with stray fields to the magnetic flux density at this location. This interpretation is confirmed by modelling of the distribution of transport currents in the superconductor using a 3D finite element model.
Article
In order to optimize the design of undulators using high-temperature superconductor (HTS) bulks we have developed a method to estimate the critical current density (J_{c}) of each bulk from the overall measured magnetic field of an undulator. The vertical magnetic field was measured along the electron-beam axis in a HTS bulk-based undulator consisting of twenty Gd-Ba-Cu-O (GdBCO) bulks inserted in a 12-T solenoid. The J_{c} values of the bulks were estimated by an inverse analysis approach in which the magnetic field was calculated by the forward simulation of the shielding currents in each HTS bulk with a given J_{c}. Subsequently the J_{c} values were iteratively updated using the precalculated response matrix of the undulator magnetic field to J_{c}. We demonstrate that it is possible to determine the J_{c} of each HTS bulk with sufficient accuracy for practical application within around 10 iterations. The precalculated response matrix, created in advance, enables the inverse analysis to be performed within a practically short time, on the order of several hours. The measurement error, which destroys the uniqueness of the solution, was investigated and the points to be noted for future magnetic field measurements were clarified. The results show that this inverse-analysis method allows the estimation of the J_{c} of each bulk comprising an HTS bulk undulator.
Article
The concept of a high-gradient trapped field magnet (HG-TFM), which incorporates a hybrid system of two (RE)BaCuO superconducting bulk components with different functions, was proposed in 2021 by the authors based on the results of numerical simulations. The HG-TFM as a desktop-type magnet can be a more effective way to generate a higher magnetic field gradient product of B z ·dB z /dz (> -1400 T ² /m, as calculated for a pure water), which can realize a quasi-microgravity space applicable for Space Environment Utilization on a laboratory scale. In this study, to validate the quasi-microgravity space in the HG-TFM, a prototype HG-TFM apparatus has been built using a slit-bulk TFM and stacked full-TFMs (without slits) with inner diameters of 36 mm. After field-cooled magnetization (FCM) from 8.60 T at 21 K, a trapped field of B T = 8.57 T was achieved at the center (i.e., at the bottom of a room temperature bore of 25 mm diameter outside the vacuum chamber), and consequently, a maximum B z ·dB z /dz = -1930 T ² /m was obtained at the intermediate position between the slit-bulk TFM and the stacked full-TFM. Magnetic levitation was demonstrated successfully for bismuth particles and a pure water drop, which validates the quasi-microgravity environment in the HG-TFM. Based on numerical simulation results of the trapped field profile, it is concluded that the reason for the instability of the levitated targets is because of the repulsive magnetic force applied along the horizontal plane. The levitating state can be controllable, for example, by changing the operating temperature, which would allow objects to levitate statically along the central axis.
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A production run of 60 melt-textured YBCO trapped field magnets (TFMs), 2 cm in diameter, is reported. The TFMs have pinning centers of Y211 and (Pt0.4U0.6)YBa3O6 deposits and also damage tracks of ions from uranium fission. The resulting average trapped field at the center of the seed-side surface is 〈BT(r = 0)〉 = 2.04 T at 77 K. The rms spread in BT is 5.9%. TFM samples rejected due to problems with the SmBCO seeds totaled ~10%, and an additional 2% were lost due to cracking under magnetic pressure. Methods to significantly reduce these losses are discussed. The ratio of BT on the TFM bottom to that on the seed side is ~67%. Evidence of a method to raise this ratio to 1.0 is presented. The magnitude and time dependence of the radioactivity resulting from the uranium fission are reported.
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The development of bulk high-temperature superconductors (HTSs) and their applications has today come to a point where the mechanical response to high magnetic fields may be more important than their critical-current density and large-grain property. Reviewed in this article are the recent studies of the magneto-elastic effects which are caused by flux pinning in the superconductors. This includes the work on the giant irreversible magnetostriction and internal stress, which often cause fatal cracking of the HTS bulks as they become magnetized. The cracking is a problem that today accompanies the quest for the highest trapped field values, and the latest development in this area is also presented. While the first part is an overview of experimental efforts, the second summarizes the work done to model the pinning-induced stress and strain under various magnetic and geometrical conditions.
Article
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Improved trapped fields are reported for bulk melt-textured YBa <sub> 2 </sub> Cu <sub> 3 </sub> O <sub>7-δ</sub> (YBCO) material in the temperature range between 20 and 50 K. Trapped fields up to 12.2 T were obtained at 22 K on the surface of single YBCO disks (with Ag and Zn additions). In YBCO minimagnets, maximum trapped fields of 16 T (at 24 K) and of 11,2 T (at 47 K) were achieved using ( Zn+Ag ) and Zn additions, respectively. In all cases, the YBCO disks were encapsulated in steel tubes in order to reinforce the material against the large tensile stress acting during the magnetizing process and to avoid cracking. We observed cracking not only during the magnetizing process, but also as a consequence of flux jumps due to thermomagnetic instabilities in the temperature range betweeen 20 and 30 K. © 2001 American Institute of Physics.
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Large-grain high-temperature superconductors of the form RE-Ba-Cu-O (where RE is a rare-earth element) can trap magnetic fields of several tesla at low temperatures, and so can be used for permanent magnet applications. The magnitude of the trapped field is proportional to the critical current density and the volume of the superconductor. Various potential engineering applications for such magnets have emerged, and some have already been commercialized. However, the range of applications is limited by poor mechanical stability and low thermal conductivity of the bulk superconductors; RE-Ba-Cu-O magnets have been found to fracture during high-field activation, owing to magnetic pressure. Here we present a post-fabrication treatment that improves the mechanical properties as well as thermal conductivity of a bulk Y-Ba-Cu-O magnet, thereby increasing its field-trapping capacity. First, resin impregnation and wrapping the materials in carbon fibre improves the mechanical properties. Second, a small hole drilled into the centre of the magnet allows impregnation of Bi-Pb-Sn-Cd alloy into the superconductor and inclusion of an aluminium wire support, which results in a significant enhancement of thermal stability and internal mechanical strength. As a result, 17.24 T could be trapped, without fracturing, in a bulk Y-Ba-Cu-O sample of 2.65 cm diameter at 29 K.
Article
With its comprehensive review of the current knowledge and the future requirements in the field, this book presents all the features of bulk high temperature superconducting materials. Starting from physical and chemical fundamentals, the authors move on to portray methods and problems of materials processing, thoroughly working out the characteristic properties of bulk superconductors in contrast to long conductors and films. They provide a wide range of specific materials characteristics with respect to the latest developments and future applications guiding from fundamentals to practical engineering examples. The authors are all leading international specialists involved in the field of high TC superconductor bulk materials since the beginning. Of utmost interest to engineers, scientists, and PhD students working in this field.
Article
It is well known that the efficiency of a wireless power transfer (WPT) system depends on the resistance of the transmitting and receiving coils, especially for the case of low frequency. Since the ac loss of high temperature superconductors (HTS) is much lower than that of conventional conductors, using high temperature superconductors for WPT system is a good way to increase power transfer efficiency. Here, several kinds of WPT experiments were designed and conducted by use of HTS and conventional conductor (copper) coils, respectively. The results are presented and analyzed. It is shown that the behavior of HTS WPT system is similar to that of a conventional WPT system, but the efficiency of WPT system is much higher by use of HTS coils and HTS coil is more suitable for being as a transmitting coil than as a receiving one.
Article
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.
Article
The ability to generate a permanent, stable magnetic field unsupported by an electromotive force is fundamental to a variety of engineering applications. Bulk high temperature superconducting (HTS) materials can trap magnetic fields of magnitude over ten times higher than the maximum field produced by conventional magnets, which is limited practically to rather less than 2 T. In this paper, two large c-axis oriented, single-grain YBCO and GdBCO bulk superconductors are magnetized by the pulsed field magnetization (PFM) technique at temperatures of 40 and 65 K and the characteristics of the resulting trapped field profile are investigated with a view of magnetizing such samples as trapped field magnets (TFMs) in situ inside a trapped flux-type superconducting electric machine. A comparison is made between the temperatures at which the pulsed magnetic field is applied and the results have strong implications for the optimum operating temperature for TFMs in trapped flux-type superconducting electric machines. The effects of inhomogeneities, which occur during the growth process of single-grain bulk superconductors, on the trapped field and maximum temperature rise in the sample are modelled numerically using a 3D finite-element model based on the H-formulation and implemented in Comsol Multiphysics 4.3a. The results agree qualitatively with the observed experimental results, in that inhomogeneities act to distort the trapped field profile and reduce the magnitude of the trapped field due to localized heating within the sample and preferential movement and pinning of flux lines around the growth section regions (GSRs) and growth sector boundaries (GSBs), respectively. The modelling framework will allow further investigation of various inhomogeneities that arise during the processing of (RE)BCO bulk superconductors, including inhomogeneous Jc distributions and the presence of current-limiting grain boundaries and cracks, and it can be used to assist optimization of processing and PFM techniques for practical bulk superconductor applications.
Article
Large, single grains of Y-Ba-Cu-O (YBCO) have been batch-processed to date by the top seeded melt growth (TSMG) process using NdBCO or SmBCO seed crystals. It has proved difficult, however, to economically batch-process light rare earth (LRE) LRE-Ba-Cu-O bulk high temperature superconductors, which have higher critical current densities and irreversibility fields than YBCO, and therefore greater potential for high field engineering applications. In this paper, we report a novel batch-process based on a cheap, readily available generic seed crystal, developed recently at Cambridge, and a TSMG melt processing technique based on cold seeding in air for the batch fabrication of Gd-Ba-Cu-O-Ag single grains. The superconducting properties of the (LRE)BCO single grains fabricated by this process are, in all respects, equivalent to those processed more conventionally in a reduced oxygen atmosphere.
Article
Ceramic–metal joining techniques have traditionally been concerned with topics such as interfacial reactions between glass/ceramic, wetting, graded seals, active metal braze reactions, residual tensile stresses, atom migration, temperature and atmospheric effects, etc. These reactions are complex and require substantial trial and error and analytical techniques to develop the proper interfaces for reliable bonding. In contrast, we have developed a simple shrink-fit ceramic/metal join for use as a new ceramic wafer retaining ring in chemical mechanical planarization. The join relies on thermal coefficient of expansion mismatch between the metal and the ceramic. The join requires no other materials such as braze or metallization and can be performed with one heating cycle in a low temperature oven. In addition, the join is reversible with reheating. This article details design considerations for developing this bond. In addition, stress analysis results using finite element analysis are presented and discussed. © 2000 American Vacuum Society.
Article
We have made measurements of the evanescent decay of the irreversible magnetization induced by magnetic cycling of solid superconducting cylinders in order to elucidate the mechanisms of Anderson's thermally activated flux-creep process. A superconducting quantum interferometer device coupled to the creep specimen by a superconducting flux transformer made possible observations of flux changes with a resolution of one part in 109. The general applicability of Anderson's theory of flux creep was confirmed and the results were analyzed to show that: (1) The total flux in the specimen changed logarithmically in time, i.e., Deltaphi~lntt0. (2) The logarithmic creep rate dphidlnt is proportional to the critical current density Jc and to the cube of the specimen radius. (3) The logarithmic creep rate appears to be only weakly temperature-dependent because a proportionality to T is nearly compensated by the proportionality to Jc, which decreases as T increases. (4) The creep process is a bulk process that is not surface-limited (in this case). (5) Flux enters and leaves the surface in discrete events containing from about one flux quantum up to at least 103 flux quanta. (6) On departing from the critical state to a subcritical condition, the creep process tends to remain logarithmic in time, but the rate is decreased exponentially by decreasing T and is decreased extremely rapidly by backing off of the applied field from the critical state. (7) At magnetic fields H
Article
Remanent induction was measured for a superconducting sample of Zr-26% wt. V. The results agree qualitatively with Bean's model for weak fields.
Conference Paper
The development of high-temperature superconductors (HTSs) can be broadly generalized into thin-film electronics, wire applications, and bulk applications. We consider bulk HTSs to include sintered or crystallized forms that do not take the geometry of filaments or tapes, and we discuss major applications for these materials. For the most part applications may be realized with the HTSs cooled to 77 K, and the properties of the bulk HTSs are often already sufficient for commercial use. A non-exhaustive list of applications for bulk HTSs includes trapped field magnets, hysteresis motors, magnetic shielding, current leads, and magnetic bearings. These applications are briefly discussed in this paper.
Article
High trapped fields were found in zinc-doped, bulk melt-textured YBa2Cu3O7−x (YBCO) material showing a pronounced peak effect in the field dependence of the critical current density. Trapped fields up to 1.1 T were found at 77 K at the surface of a YBCO disk (diameter 26 mm, height 12 mm). Very high trapped fields up to 14.35 T were achieved at 22.5 K for a YBCO disk pair (diameter 26 mm, height 24 mm) by the addition of silver and using a bandage made of stainless steel. The pinning forces and trapped fields obtained in bulk YBCO material are compared with results reported for melt-processed NdBa2Cu3O7−x and SmBa2Cu3O7−x.© 2000 American Institute of Physics.
Article
We fabricated a single-domain Gd–Ba–Cu–O bulk superconductor 65 mm in diameter and studied the microstructure, superconducting and field-trapping properties. Melt-processing was performed under a controlled oxygen partial pressure of 1.0% using a precursor containing Gd123 and Gd211 powders in a molar ratio of 2:1, with 0.5 wt% of Pt and 20 wt% of Ag2O added. The distribution of Ag and Gd211 particles was almost homogeneous. The addition of Ag was very effective in reducing the amount of cracking in the sample. The maximum trapped magnetic field recorded was 3.05 T at 77 K. We also measured the trapped field between two Gd–Ba–Cu–O bulk samples in order to minimize the demagnetizing effect and found that the trapped field reached 4.3 T at 77 K.
Article
A series of experiments has been carried out on the flux trapping and shielding capabilities of a flat strip of Nb‐Ti/Cu composite material. A circular piece of material from the strip was tested in a uniform field directed perpendicularly to the surface of the sample. Profiles of the normal component of the field along the sample diameter were measured. The critical‐state model was adapted for this geometry and proved capable of reproducing the measured field profiles. Model curves agreed well with experimental field profiles generated when the full sample was in the critical state, when only a portion of the sample was in the critical state, and when profiles were obtained after the direction of the rate change of the magnetic field was reversed. The adaption of the critical‐state model to disk geometry provides a possible method either to derive values of the critical current from measurements of field profiles above thin flat samples, or to predict the trapping and shielding behavior of such samples if the critical current is already known. This method of determining critical currents does not require that samples be formed into narrow strips or wires, as is required for direct measurements of J c , or into tubes or cylinders, as is usually required for magnetization‐type measurements. Only a relatively small approximately circular piece of material is needed. The method relies on induced currents, so there is no need to pass large currents into the sample. The field‐profile measurements are easily performed with expensive Hall probes and do not require detection of the resistive transition of the superconductor.
Article
Quasi-permanent magnets made of melt-textured YBa2Cu3O7−δ (MT-YBCO) superconductor can now trap multi-tesla fields, Bt. The interaction of the trapped field and the critical current causes an outward pressure, proportional to Bt2, which can crack the magnet. We have done an experiment to observe such cracking in a mini-magnet fabricated from four MT-YBCO discs activated at 49 K using an applied of 14 T. We have compared the results to existing theories which describe magnetic pressure in a trapped-field magnet (TFM) previously activated. We find that a modification is needed to describe magnetic pressure during the process of activation. We present the experimental results and the expanded theory, based on the simple Bean model. Theory and experiment show good agreement. We find that cracking is more likely during activation, and conclude that 10 T is achievable in TFM's composed of present materials. Cracking is most probable at the center of a TFM, with the cracks running radially outward.
Article
All nine independent elastic constants cij of a YBa2Cu3O7-delta monocrystal were determined at room temperature using resonant ultrasound spectroscopy. Shear and Young moduli obtained from the cij by the Voigt-Reuss-Hill averaging method agree well with the pulse-echo results on a polycrystal. The Debye temperature calculated from the elastic constants agrees with the specific-heat measurement.
Article
Bulk high-temperature superconductors (HTSs) enable the opportunity to develop several unique applications in electrical power that are not feasible with superconducting or normal wires. The large current carrying capacity and low thermal conductivity of the HTSs allows relatively short lengths to carry large currents to low-temperature devices without introducing heat to the device. Such current leads can dramatically reduce the refrigeration requirements for devices such as SMES. The HTSs make a relatively sharp transition to a highly resistive state when the critical current density is exceeded, and this effect has suggested their use for resistive fault current limiters. The bulk HTSs may also take the form of large single-grained superconductors within which circulating currents may flow at large current density without loss. They are capable of developing magnetizations, similar to that of permanent magnets, but with much larger magnetic fields. In this case, they may be used as field-trapping components. Applications in this case include brushless synchronous motors, laboratory magnets, magnetic separation, and magnetron sputtering. The bulk HTSs may also be used as diamagnetic objects in magnetic circuits to provide new types of power devices. One application that uses this effect is an inductive fault current limiters, in which the HTS shields an iron core in an inductive circuit until some current level is exceeded. This transition increases the component from low impedance to high impedance. The diamagnetic property may also be used to create low-loss magnetic bearings for use in efficient energy-storage flywheel devices or sensitive instrumentation. The combination of diamagnetic shielding and field trapping has suggested their use in motor designs analogous to hysteresis motors. Laboratory prototypes for all of these devices have been constructed and tested, and in some cases the devices have been field tested in actual power systems. Improvements in HTS properties, such as flux pinning, mechanical strength, and the ability to grow large grains, have greatly improved the economics of applications that use bulk HTS.
  • J E Shigley
  • C Mischke
Shigley J E and Mischke C R 2001 Mechanical Engineering Design 6th edn (New York: McGraw-Hill Education) pp 62–3
  • G Krabbes
Krabbes G et al 2006 High Temperature Superconductor Bulk Materials (Weinheim: Wiley) p 181