Maximum Levitation Force Research Articles

Magnetic Levitation Force of Bulk YBaCuO Pieces as a Function of Texture

Very well textured YBaCuO forms can be produced by means of seed crystals implanted in an YBaCuO melt. Narrow distributions of the directions (FWHM < 6°) of the c-axes of the crystalline grains as well as the a- and b-axes, respectively, are required for this purpose. Small angles between the c-axes of adjacent grains, and small angles between the a- and b-axes, respectively, of the neighbors, constitute but small obstacles, in the path of the superconducting current induced. If the entire volume of the melt-textured forms, in this case YBaCuO cylinders, is well textured, and if no random volume fractions remain, a maximum inducible superconducting current in the superconductor can be achieved and, thus, a maximum magnetic repellent force against the inducing permanent magnet, can be attained. This ensures maximum magnetic levitation force for a superconducting self-stabilizing magnetic bearing.

Physical characteristics of electromagnetic levitation processing

Electromagnetic levitation has developed from a pure physical phenomenon into a practical containerless processing technique in the fields of both applied physics and materials science. In order to obtain a better understanding of this processing technique, two typical levitation coils were designed and the physical characteristics in levitation droplets suspended in these two coils, such as electromagnetic field, levitation force field, total levitation force, and power absorption, were analyzed numerically and calculated in this paper. It was found that the eddy current density, together with the magnetic flux density and levitation force density, increases rapidly with radius as it approaches sample surface. The maximum levitation force produced by coil A is larger than that of coil B, whereas the levitated sample can obtain less power absorption at the equilibrium position in the former coil than that in the latter one. Moreover, the calculated results also demonstrated that the levitation ability decreases as the atomic number increases. The larger the material's electrical resistivity, the easier the samples can obtain more power absorption.

Levitation characteristics of the HTSC-permanent magnet hybrid flywheel system

A basic experimental device for a flywheel system using high temperature superconducting material (HTSC) is introduced. In this system, a circular shaped permanent magnet is installed on the rotor, and a YBaCuO plate is used for the stator. To increase the levitation force of the flywheel, an additional circular permanent magnet is installed under the YBaCuO plate in the stator. The maximum levitation force and rotational loss were examined. From the experimental results, this hybrid system shows better levitation characteristics than that without an additional permanent magnet.

Texture and Magnetic Levitation Force of Melt-Textured YBaCuO Cylinders

To investigate the correlation between the levitation force of YBaCuO cylinders when approached by a permanent magnet and the texture of these YBaCuO cylinders some of these specimens were selected which are free of microcracks, have the same oxygen load, show no isotropic fraction or other undesired parasitic c-axis orientations. To gain a maximum levitation force the c-axis orientation of the crystalline domains has to have a small divergence between the c-axis and the cylinder axis. By measurements of the (002) pole figures by neutron diffraction with a mesh width no more than 6° undesired c-axis orientations have been analyzed. The distribution of the c-axis near the cylinder axis has been measured at the (005) reflection of 7 times higher intensity than the (002) reflection. The angular limit within which lie 94% of all c-axis orientations is a practical value for comparison of the c-axis orientations and the levitation forces of the different YBaCuO cylinders.

The effect of excess Y 2O 3 addition on the levitation force of melt processed YBCO bulk superconductors

The YBCO superconductors with Y 2O 3 addition were prepared by a modified melt textured process and the effects of excess Y 2O 3 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 Y 2O 3, whereas the solid state reaction temperature increases slightly as the Y 2O 3 addition rises. The maximum levitation forces (MLF) are much different for samples with different Y 2O 3 addition. It is found that the optimum Y 2O 3 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.

Preparation and characterization of melt-textured Nd 1+xBa 2−xCu 3O y made in air

High quality melt-textured Nd 1+xBa 2−xCu 3O y bulks have been prepared through a novel technology carried out in air. In present study, a modified melt processing technology is employed to prepare the melt-textured Nd 1+xBa 2−xCu 3O y samples, and a post-annealing in flowing Ar is used to obtain the high Tc phase. AC susceptibility measurement shows that the critical temperature has reached 94.5K. The maximum levitation force is 7.4N for a sample with a diameter of 18mm. The Jc values are 2.4 × 10 4 A/cm 2 (0T,77K), 1.7 × 10 4 A/cm 2 (1T, 77K) and 3.3 × 10 5 A/cm 2 (8T, 21K). The fishtail effect is relatively obvious in 40–60K.

Influence of superconductor properties on magnetic levitation force

We present calculated results of the maximum levitation force in a permanent magnet-superconductor system for a wide range of values of superconductor properties. We discus the optimum range of these values in order to achieve large levitation forces.

Optimized configurations of autostable superconducting magnetic bearings for practical applications

In order to establish an optimized bearing design for a flywheel for energy storage, we have studied model bearing configurations involving bulk YBCO pellets and double-dipole magnet configurations. We were interested to see what the correlation is between the maximum attainable levitation force, measured for a typical bearing gap of 3 mm, and the separation between the magnetic poles. Equal polarity (north-north) and alternative polarity (north-south) configurations were investigated. The maximum levitation force was obtained with the alternate polarity arrangement for a separation between the magnetic poles of 6 mm. It represents an increase of 19% compared to a nonoptimized configuration. Our experiments demonstrate that configurations of superconducting magnetic bearings can be optimized to obtain better levitation properties.