A fully superconducting magnetic suspension structure has been designed and constructed for the purpose of superconducting bearing applications in flywheel energy storage systems. A thrust type bearing and two journal type bearings, those that are composed of melt textured high-Tc superconductor YBCO bulks and Nd-Fe-B permanent magnets, are used in the bearing system. The rotor dynamical behaviors, including critical speeds and rotational loss, are studied. Driven by a variable-frequency three-phase induction motor, the rotor shaft attached with a 25 kg flywheel disc can be speeded up to 15 000 rpm without serious resonance occurring. Although the flywheel system runs stably in the supercritical speeds region, very obvious rotational loss is unavoidable. The loss mechanism has been discussed in terms of eddy current loss and hysteresis loss.

It is well known that a fine and homogeneous distribution of Y2BaCuO5 (Y211) phase particles in single-grain Y-Ba-Cu-O (YBCO) bulk superconductors is essential for improving field-trapping ability. However, the size and concentration of Y211 phase particles in the fully melt-processed superconducting bulk increase significantly with the distance from the seed, which results in the accumulation of Y211 phase particles and the degradation of superconducting properties. In this paper, we report a new method of fabricating single-grain YBCO using layered precursor pellets. Using the top-seeded melt-textured growth process, single-grain YBCO bulk superconductors of about 22 mm in diameter and 9 mm in thickness were fabricated from layered precursor pellets and standard precursor pellets, respectively. The layered precursor pellets consist of precursor powders with 40 mol% Y211 at the top, 30 mol% Y211 in the middle and 20 mol% Y211 at the bottom of the whole pellets, while standard precursor pellets are prepared from precursor powders with only 40 mol% Y211. The growth morphology, microstructure and magnetic flux properties of the layered samples and standard samples were comparatively studied. The results proved that the layered precursor pellets allow a sufficient growth in the c-growth sector and a more uniform distribution of the Y211 phase in the matrix. The distribution of Y211 phase particles is qualitatively explained by the prevalent trapping/pushing theory. The trapped field at 77 K reaches 0.8 T, nearly 29% higher than the standard sample. The present results are very valuable for further improving the properties of YBCO bulk superconductors.

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The modified top-seeded melt-textured growth technique for fabricating single grain Y–Ba–Cu–O (YBCO) bulk superconductors with high field-trapping ability by using modified precursor pellets was reported. The modified precursor pellets are composed of different precursor powders YBa2Cu3O (Y123) + x mol% Y2BaCuO5 (Y211) + 1 wt% CeO2 without any further chemical doping. The modified YBCO bulks up to 25 and 34 mm in diameter were successfully fabricated from the modified precursor pellets. Microstructural observation results showed that the modified YBCO bulk exhibited a homogeneous distribution of Y211 phase particles, which was qualitatively explained by the solute diffusion growth model in combination with the trapping/pushing theory. As a result, it is notable that the peak trapped field values of 0.91 T (maximum 0.96 T) and 1.2 T (maximum 1.28 T) at 77 K were achieved for 25 and 34 mm modified YBCO bulks, respectively. In a word, the results from present work are very helpful to understand the melt growth mechanism and to further improve the properties of YBCO bulk superconductors for practical applications.