X.D. Tang

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.

Effects of Heat Treatments on the Nb3Sn Composite Strands

Nb3Sn superconductors are widely used in high magnetic field application. Internal tin processed Nb3Sn wires used for ITER coils (at 4.2K, 12T) were heated by two steps, local heat treatment and reaction heat treatments. The superconducting properties of Nb3Sn were investigated as a function of reaction heat treatment (HT) for strands during 625°C~665°C.To study the heat treatment effects on Jcn and n-value of Nb3Sn strands, different HT-parameters, i.e., annealing temperature and times, were applied on the Nb3Sn multifilament strands.

Analysis of the morphology and chemical composition at the growth front of YBCO bulks

The morphology and chemical composition at the growth front of YBCO bulks have been investigated to make clear the stopped growth mechanism in the samples which have covered the whole melt growth process. It is found that the breakdown of quasi-single crystal growth occurs when the liquid phase ahead of the growth front becomes rich in copper and depleted in yttrium and barium. To meet the needs for maintaining the continuous growth of YBCO, the composition of Y, Ba and Cu has to be adjusted to be rich in yttrium and barium in the liquid phase ahead of the growth front during the melt growth process for growing large YBCO bulk superconductors.