Abstract
Bulk, single grain (RE)Ba2Cu3O7−δ [(RE)BCO, where RE is a rare earth element or yttrium] high temperature superconductors exhibit significant potential for use in a variety of engineering applications due to their ability to trap large magnetic fields, which can be up to ten times greater than those generated by conventional, iron-based magnets. Limitations on the maximum size to which single grains can be grown, however, are a major obstacle to the further development of these materials. Indeed, multiple samples are often required to achieve the required superconducting properties in particular applications. The geometry of bulk (RE)BCO single grain samples plays an important role in determining the superconducting properties of a given technical arrangement. In order to gain a better understanding of the full application potential of bulk single grain superconductors, three relatively long, cylindrical YBCO single grains of different diameters were fabricated and their trapped field and total trapped flux measured at 77 K as a function of sample height. The effects of size and aspect ratio of YBCO single grains on these key applied properties have been investigated experimentally and the results compared qualitatively with the predictions of an established theoretical model. Conclusions based on the trapped field measurements on a variety of single grain samples are presented in this study and the possibilities of using assemblies of smaller samples for engineering devices, in particular, are discussed.
Highlights
Bulk, single grain (RE)Ba2Cu3O7−δ [(RE)BCO, where RE is a rare earth element or yttrium] high temperature superconductors exhibit significant potential for exploitation in a variety of engineering applications due to their ability to trap large magnetic fields of up to ∼18 T [1]
Measurements of trapped fields and total flux of three YBCO single grains of diameter 16, 20 and 25 mm and sub-specimens of these grains are consistent with the predictions of Eisterer’s model that the trapped field saturates for aspect ratios where 0.67 < H/R < 1, the microstructures and properties of the samples used in this study are significantly less uniform than that assumed in this model
Measurements of the total flux of three single grain YBCO samples have revealed some interesting trends in the relation between sample geometry and trapped field
Summary
Single grain (RE)Ba2Cu3O7−δ [(RE)BCO, where RE is a rare earth element or yttrium] high temperature superconductors exhibit significant potential for exploitation in a variety of engineering applications due to their ability to trap large magnetic fields of up to ∼18 T [1]. It is known from previous modelling that the trapped field in a cylindrical bulk superconductor saturates at a given height for a sample of a fixed diameter [4] This is consistent with the observation by Eisterer that the best aspect ratio, height/radius (H/R), of a YBCO single grain is between 0.67 and 1, which ‘seems to be a good compromise between a high trapped field and a reasonable amount of superconductor’ [4]. We report an investigation of the effect of size and aspect ratio on the superconducting properties of YBa2Cu3O7−δ (YBCO) single grains This is directly relevant to applications that require high field, high total flux and a known field distribution. The results of this study have been used successfully to assemble smaller sample arrangements of single grain bulk (RE)BCO superconductors that generate either higher maximum or more uniform trapped fields
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