A Reliable Method for Recycling (RE)-Ba-Cu-O (RE: Sm, Gd, Y) Bulk Superconductors

Single grain (RE)-Ba-Cu-O (RE: Sm, Gd, Y) high temperature superconductors are able to generate high magnetic fields. However, the relatively high cost of the raw materials and the low yield of the manufacturing process have impeded the development of practical applications of these materials to date. This article describes a simple, reliable and economical method of recycling failed bulk (RE)-Ba-Cu-O (RE: Sm, Gd, Y) samples. Sixty-four failed bulk samples, with diameters up to 31 mm, were recycled with a yield of 90%. The key innovation in this recycling process involves reintroducing the liquid phase into the melt process, which is normally lost during the primary peritectic processing of these materials. This enables the direct re-growth of failed samples from solid form without the need for re-grinding into powder. We also demonstrate that the superconducting performance and microstructure of the recycled samples is similar to that of the primary grown samples.We acknowledge the Engineering and Physical Sciences Research Council (EPSRC grant ref.EP/K02910X/1) for financial support.This is the final version. It first appeared at http://dx.doi.org/10.1111/jace.1368

The use of buffer pellets to pseudo hot seed (RE)-Ba-Cu-O-(Ag) single grain bulk superconductors

Reliable seeding of the superconducting (RE)Ba₂Cu₃O₇-δ (RE-123) phase is a critical step in the melt growth of large, single grain, (RE)BaCuO [(RE)BCO] bulk superconductors. Recent improvements to the top seeded melt growth (TSMG) processing technique, which is an established method of fabricating bulk (RE)BCO superconductors, based on the use of a buffer layer between the seed and green body preform, has improved significantly the reliability of the single grain growth process. This technique has been used successfully for the primary TSMG and infiltration melt growth (IG) of all compositions within the [(RE)BCO-Ag] family of materials (where RE = Sm, Gd and Y), and in recycling processes. However, the mechanism behind the improved reliability of the melt process is not understood fully and its effect on the superconducting properties of the fully processed single grains is not clear. In this paper, we investigate the effect of the use of a buffer pellet between the seed and green body on the microstructure, critical current, critical temperature and trapped field of the bulk superconductor. We conclude that the introduction of the buffer pellet evolves the melt growth process towards that observed in the technologically challenging hot seeding technique, but has the potential to yield high quality single grain samples but by a commercially viable melt process.This work was supported by the Engineering and Physical Sciences Research Council [EPSRC, grant number EP/K02910X/1] and King Abdulaziz City for Science and Technology [KACST].This is the final version of the article. It was first available from IOP Publishing via http://dx.doi.org/10.1088/0953-2048/29/1/015010 Additional data related to this publication is available at the University of Cambridge data repository [https://www.repository.cam.ac.uk/handle/1810/249091]. All other data accompanying this publication are directly available within the publication

Design Optimization of a Hybrid Trapped Field Magnet Lens (HTFML)

The concept of a hybrid trapped field magnet lens (HTFML) was recently proposed by the authors, which consists of a trapped field magnet (TFM) cylinder exploiting the “vortex pinning effect,” combined with a superconducting bulk magnetic lens exploiting the “diamagnetic shielding effect.” This HTFML can generate, within its bore, a magnetic field higher than the applied magnetic field, even after external field decreases to zero. In this paper, a design optimization of the inner GdBaCuO magnetic lens within the GdBaCuO TFM cylinder was carried out using numerical simulations based on the finite element method, in order to maximize the concentrated magnetic field. The HTFML with an optimized shape and size achieved a concentrated magnetic field of Bc = 5.6 and 12.8 T at the center of the lens for applied magnetic fields of Bapp = 3 and 10 T, respectively. A maximum tensile stress of +135 MPa exists in the outer GdBaCuO TFM cylinder during the magnetizing process for Bapp = 10 T, which exceeds the fracture strength of the bulk. This result suggests that mechanical reinforcement is necessary to avoid mechanical fracture under such high magnetic field conditions

Multiple seeding for the growth of bulk GdBCO-Ag superconductors with single grain behaviour

Rare earth–barium–copper oxide bulk superconductors fabricated in large or complicated geometries are required for a variety of engineering applications. Initiating crystal growth from multiple seeds reduces the time taken to melt-process individual samples and can reduce the problem of poor crystal texture away from the seed. Grain boundaries between regions of independent crystal growth can reduce significantly the flow of current due to crystallographic misalignment and the agglomeration of impurity phases. Enhanced supercurrent flow at such boundaries has been achieved by minimising the depth of the boundary between $\small \textit{A}$ growth sectors generated during the melt growth process by reducing second phase agglomerations and by a new technique for initiating crystal growth that minimises the misalignment between different growth regions. The trapped magnetic fields measured for the resulting samples exhibit a single trapped field peak indicating they are equivalent to conventional single grains.The authors acknowledge support from the Engineering and Physical Sciences Research Council EP/K02910X/1.This is the final version of the article. It first appeared from the Institute of Physics via 10.1088/0953-2048/30/1/01500

Improvement of radar ice-thickness measurements of Greenland outlet glaciers using SAR processing

This is the published version, also available here: http://dx.doi.org/10.3189/172756402781816852.Extensive aircraft-based radar ice-thickness measurements over the interior and outlet-glacier regions of the Greenland ice sheet have been obtained by the University of Kansas since 1993, with the latest airborne surveys conducted in May 2001. The radar has evolved during this period to a highly versatile system capable of characterizing ice thickness over a wide variety of ice-sheet conditions. Before 1997, the digital system was limited, only capable of storing incoherent data or coherent data with a very large number of presumed signals at a low pulse-repetition frequency. In 1998, the radar was upgraded with modern components allowing coherent data to be stored with a small number of presumed returns for 1024 range cells at a high pulse-repetition frequency.The new data on ice thickness of Greenland outlet glaciers are archived and made available to the scientific community in the form of radar echograms and derived ice thickness at http://tornado.rsl.ukans.edu/Greenlanddata.htm. The U.S. National Snow and Ice Data Center (NSIDC) also provides a link to these data, and NSIDC will eventually serve as the permanent archive of these data. Improvements in radar sensitivity in outlet-glacier regions have been achieved by collecting coherent radar data and applying various signal-processing techniques. Deep outlet-glacier channels that were previously unresolved with incoherent data can now be mapped using a coherent signal, signal conditioning and synthetic aperture radar (SAR) processing

Respiratory Inductance Plethysmography to Assess Fatigability during Repetitive Work

publishersversionPeer reviewe

Pulsed-field magnetisation of Y-Ba-Cu-O bulk superconductors fabricated by the infiltration growth technique

Funder: King Abdulaziz City for Science and Technology; doi: http://dx.doi.org/10.13039/501100004919Abstract: 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 Y2BaCuO5 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

A novel pre-sintering technique for the growth of Y–Ba–Cu–O superconducting single grains from raw metal oxides

Most established top seeded melt growth (TSMG) processes of bulk, single grain Y–Ba–Cu–O (YBCO) superconductors are performed using a mixture of pre-reacted precursor powders. Here we report the successful growth of large, single grain YBCO samples by TSMG with good superconducting properties from a simple precursor composition consisting of a sintered mixture of the raw oxides. The elimination of the requirement to synthesize precursor powders in a separate process prior to melt processing has the potential to reduce significantly the cost of bulk superconductors, which is essential for their commercial exploitation. The growth morphology, microstructure, trapped magnetic field and critical current density, $J_\text{c}$, at different positions within the sample and maximum levitation force of the YBCO single grains fabricated by this process are reported. Measurements of the superconducting properties show that the trapped filed can reach 0.45 T and that a zero field $J_\text{c}$ of 2.5 × 10$^4$ A cm$^{−2}$ can be achieved in these samples. These values are comparable to those observed in samples fabricated using pre-reacted, high purity commercial oxide precursor powders. The experimental results are discussed and the possibility of further improving the melt process using raw oxides is outlined.EP/P00962X/1, National Natural Science Foundation in China (No. 51572164), the China Scholarship Council (No. 201506875065

Composite stacks for reliable > 17 T trapped fields in bulk superconductor magnets

Trapped fields of over 20 T are, in principle, achievable in bulk, single-grain high temperature cuprate superconductors. The principle barriers to realizing such performance are, firstly, the large tensile stresses that develop during the magnetization of such trapped-field magnets as a result of the Lorentz force, which lead to brittle fracture of these ceramic-like materials at high fields and, secondly, catastrophic thermal instabilities as a result of flux movement during magnetization. Moreover, for a batch of samples nominally fabricated identically, the statistical nature of the failure mechanism means the best performance (i.e. trapped fields of over 17 T) cannot be attained reliably. The magnetization process, particularly to higher fields, also often damages the samples such that they cannot repeatedly trap high fields following subsequent magnetization. In this study, we report the sequential trapping of magnetic fields of ~ 17 T, achieving 16.8 T at 26 K initially and 17.6 T at 22.5 K subsequently, in a stack of two Ag-doped GdBa2Cu3O7-{\delta} bulk superconductor composites of diameter 24 mm reinforced with (1) stainless-steel laminations, and (2) shrink-fit stainless steel rings. A trapped field of 17.6 T is, in fact, comparable with the highest trapped fields reported to date for bulk superconducting magnets of any mechanical and chemical composition, and this was achieved using the first composite stack to be fabricated by this technique

Factors Affecting the Growth of Multiseeded Superconducting Single Grains

© 2016 American Chemical Society.Single grain, rare earth-barium-copper oxide [(RE)BCO] bulk superconductors, fabricated either individually or assembled in large or complicated geometries, have a significant potential for a variety of potential engineering applications. Unfortunately, (RE)BCO single grains have intrinsically very low growth rates, which limits the sample size that may be achieved in a practical, top seeded melt growth process. As a result, a melt process based on the use of two or more seeds (so-called multiseeding) to control the nucleation and subsequent growth of bulk (RE)BCO superconductors has been developed to fabricate larger samples and to reduce the time taken for the melt process. However, the formation of regions that contain non-superconducting phases at grain boundaries has emerged as an unavoidable consequence of this process. This leads to the multiseeded sample behaving as if it is composed of multiple, singly seeded regions. In this work we have examined the factors that lead to the accumulation of non-superconducting phases at grain boundaries in multiseeded (RE)BCO bulk samples. We have studied the microstructure and superconducting properties of a number of samples fabricated by the multiseeded process to explore how the severity of this problem can be reduced significantly, if not eliminated completely. We conclude that, by employing the techniques described, multiseeding is a practical approach to the processing of large high performance superconducting bulk samples for engineering applications.Engineering and Physical Sciences Research Council (Grant ID: EP/K02910X/1