W.M. Yang

The characterization of levitation force and attractive force of single-domain YBCO bulk under different field cooling process

Abstract The interaction forces were measured at 77 K by changing the field cooling distance Z fc between a YBCO bulk and a permanent magnet. It is found that the maximum levitation force ( F mlf ), maximum attractive force ( F maf ) and the gap distance ( Z maf ) corresponding to F maf can be well described by exponential laws as a function of Z fc , which allow us to predict these values according to Z fc . It is also found that the distance between the Z 0fa (gap distance corresponding to the zero force) and Z maf in the ascending process is a constant value, which can be well interpreted by the constant reduction rate of the axial component magnetic flux density along the axis line of the magnet within the constant distance. These results are very interesting to physical research and helpful for the practical designing and applications.

The effect of excess Y2O3 addition on the levitation force of melt processed YBCO bulk superconductors

Abstract The YBCO superconductors with Y2O3 addition were prepared by a modified melt textured process and the effects of excess Y2O3 addition on the levitation force of melt textured YBCO have been investigated. The results indicate that the melt temperature of YBCO samples decreases drastically with the increasing excess Y2O3, whereas the solid state reaction temperature increases slightly as the Y2O3 addition rises. The maximum levitation forces (MLF) are much different for samples with different Y2O3 addition. It is found that the optimum Y2O3 excess in YBCO for the (strong MLF) is about 10 wt.%. Combined with the microstructure and the starting composition, the results are discussed in detail.

A small Maglev car model using YBCO bulk superconductors

Models of two small Maglev cars have been made. The track was paved with NdFeB magnets. The arrangement of the magnets made it easy to get a uniform magnetic field distribution along the length of the track and a magnetic field gradient in the lateral direction. When the car with YBCO bulk superconductors was field cooled to LN2 temperature at a certain distance above the track, the car could be automatically levitated over the track and moved along the track without any obvious friction. The model can be used to demonstrate the Meissner effect and a fast transportation system to students and adults.

The effect of magnet size on the levitation force and attractive force of single-domain YBCO bulk superconductors

The levitation forces between a single-domain YBCO bulk and several magnets of different sizes have been measured at 77 K to investigate the effect of the magnet size on the levitation force. It is found that the levitation force reaches a largest (peak) value when the size of the magnet approaches that of the superconductor when the other conditions are fixed. The absolute maximum attractive force (in the field-cooled state) increases with the increasing of the magnet size, and is saturated when the magnet size approaches that of the superconductor. The maximum attractive force in the field-cooled (FC) state is much higher than that of the maximum attractive force in the zero field-cooled (ZFC) state. The results indicate that the effects of magnetic field distribution on the levitation force have to be considered during the designing and manufacturing of superconducting devices.

The effect of magnet configurations on the levitation force of melt processed YBCO bulk superconductors

Abstract The high levitation force of YBCO bulk superconductors makes it possible for many applications such as magnetic bearings, flywheels and magnetic levitation transport systems etc. But for a given superconductor, the levitation forces are much different with different magnetic field distributions. In this paper, many small magnets (10×10×10 cm 3 ) with the B=0.5 T on the top surface have been selected to investigate the effects of the magnet numbers and the configurations of the same number of magnets on the levitation force of a single-domain YBCO bulk superconductor (30 mm in diameter). It is found that the levitation force increases with the increasing of the magnet numbers (such as the levitation force increases from 18.8 to 49 N with the increasing of the magnet numbers from 1 to 12) and saturated when the size of the composed magnet becomes larger than that of the YBCO bulk. It is also found that the levitation forces are different with different magnet configurations for a given YBCO bulk and the same number of the magnets, the smaller the magnetic poles in the composed magnets, the higher the levitation force of the YBCO bulks. The results will be discussed in detail.

The relationship of levitation force between single and multiple YBCO bulk superconductors

The levitation forces have been measured for many individual and multiple single-domain YBCO bulk superconductors. It is found that the levitation force of multiple YBCO bulk is closely related with levitation force of each individual single-domain YBCO bulk (used for composing the multiple bulks). The resultant force of the multiple YBCO bulks is slightly less than the summation levitation force of each individual single-domain YBCO bulks, while each individual YBCO bulk is fixed in position the same as that in the multiple YBCO bulk. The difference is about 5%, so that we can predict the resultant levitation force of multiple YBCO bulks with various shape and complex configuration more easily. This is very important and useful for simplifying the experimental tests on superconducting devices during designing and constructions for practical applications.

New method to synthesize precursor powders for high-Tc superconductor

Abstract In this paper, a high-efficient method to synthesize high- T c superconducting precursor powders is presented. It overcomes the intrinsic weakness of traditional coprecipitation process, in which no suitable pH value can be adjusted to coprecipitate all kinds of cations completely. It is possible to synthesize superconducting precursor powders in medium scale production, and the powders synthesized by this method meet requirement of Bi-system or Y-system superconductor.

High-Quality Single-Domain SmBCO Bulks Prepared by a Sm+011 SIG Technique With New Solid Phase in Air

High-quality single-domain SmBCO bulks have been successfully produced in air by a new Sm+011 SIG method, with a new solid phase of (Sm₂O₃ + xBaCuO₂) and a liquid phase of (Y₂O₃ + 6CuO + 10BaCuO₂). The onset critical temperature (Tcon) of the SmBCO bulks increases with the increasing of x; the Tcon have reached 96 K when x = 1.4. The amount and the size of Sm211 particles in the samples decreases with the increasing of BaCuO₂ addition x. The levitation force of the samples (φ20 mm) increases from 38.47 to 44.34 N and decreases to 37.94 N with the increasing of x from 0.9 to 1.2 and 1.4. Single-domain SmBCO bulks (φ32 × 8.4 mm) with a levitation force of 98.7 N (77 K, 0.5 T) and a trapped field of 1.15 T (77 K) have been fabricated by the new Sm+011 SIG method. This result provides a very important way to fabricate high-quality single-domain SmBCO bulks in air.