The trapped field strength of HTSC stacks were measured in the temperature range T=4-80 K and dc magnetic fields up to 8 Т. A single 12 mm by 12 mm square samples were cut from commercial (RE)BCO tape 12 mm wide and then stacked together. The number of layers in the stacks was varied from n=5 to n=250. Trapped field strength was measured by means of Hall probe which was placed directly on the stacks surface. The dependences of remnant field strength B rem on number of layers in the stacks at different temperature B rem (n) as well as on temperature dependences B rem (T) at various n were obtained. It was found that B rem (n) dependences have a nonlinear character with a tendency to saturation for n > 60. The maximum remnant (trapped) field was found to be more than 2.5 Т at T=4 К. The relaxation of trapped field was studied also and it was determined that the rate of relaxation processes tends to decrease with the increase in a number of tapes in the stack. The correlation between dependency B rem (n) and dependency of magnetic levitation force measured at T=77 K at zero field cooling were found.
A new type of scalable high-temperature superconducting magnetic bearing is proposed. The bearing is based on the multilayer open windings made of coated conductor-tapes (CC-tapes). To demonstrate the possibility of manufacturing such a bearing construction we have built a working prototype and studied its characteristics. The manufactured model of bearing includes a stator, consisting of three multilayer rings (CC-tapes pancake coils) of 12 mm CC-tape and a composite rotor consisting of three rings of permanent magnets, each composed of 16 NdFeB 10 × 10 mm permanent magnets. We showed a contactless levitation of rotor relative to stator, as well as rotation of rotor and we measured load curves, namely the dependence of the rotor displacement on restoring force for axial and radial loads. Numerical simulation of bearing load characteristics has been carried out by the finite element method in the Comsol Multiphysics software. The calculation results are in a good agreement with the experimental data.
The majority of superconducting levitation systems are based on bulk superconductors. However, recently, stacks of coated conductor superconducting tapes (CC-tapes) have shown a proven potential to act as an alternative to superconducting bulks as components of a magnetic levitation system. This work primarily focuses on the influence of the critical current density on the levitation force of stacks of CC-tapes. The levitation force was measured for stacks of tapes made by different manufacturers, with different values of the critical current and substrate thickness. In our experiment, we used superconducting tapes manufactured by SuperOx, Theva and Sunam. The tapes were cut into 12 mm square pieces. The number of layers in the stack ranged from 10 to 100. Levitation forces were studied for all types of tapes and for various numbers of layers in the stack. As expected, it was found that a higher critical current corresponds to a higher levitation force. The levitation force of the stacks assembled from tapes with a higher critical current tends to saturate for lower numbers of elements in the stack.
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