Research On Electromagnetic Properties Of YBCO High Temperature Superconductor In Symmetrical And Unsymmetrical Applied Fields

Both levitation and guidance performance of a single bulk and bulk array have been studied in this paper, from the points of both experimental measurements and theoretical calculations. The high temperature superconductor (HTS) was assumed to be isotropic and the critical current density is constant independent of the applied magnetic field in the Two Dimensional Progozhin model. Its calculated levitation force in symmetrical applied field qualitatively agreed with the experimental levitation force. However the former were roughly twice more than the latter. In unsymmetrical applied fields, there were both qualitative and quantitative differences between the calculated and experiemental results. Kim model and Exponential model were employed in terms of the magnitude dependence of the critical current density on the applied magnetic field. The Kim model has several parameters to be determined, which is not fit for the numerical caculations. However, the exponential relationship in the Expoential model was fitted from the measured JC(B) curve. So the Exponential model was preferred in the calculations, and its calculated current distributions upon the vertical cross section indicate that the magnetization currents flowing in the penetration part close to the superconductor bulk's surface. But the calculated levitation force had no significant improvement in the unsymmetrical applied fields.Subsequently, the anisotropy resulting from the layer structure of YBCO superconductor was taken into account in the computation from two sides. One is to respectively consider the angle dependence of the critical current density on the applied field using the proximate cosine angle dependence and the anisotropic GL fuction angle dependence. The other side is to approximately describe the anisotropy ratio of critical current density through adjusting the layer thickness upon the vertical cross section. Furthurmore, based on the prelimary analysis of the Tripple Dimensional distribution of the magnetization current, the quasi Tripple Dimensional model was proposed, considering the differerace between the calculated bulk in Two Demensioal model and the practical sample in the experiments. Two end sections are supposed in the quasi Tripple Dimensional model, and the qualitative agreement between calculated and experimental results can be obtained. Furthuremore the newphenomenon in terms of vortex was studied, such as vortex locking, geometrical locking resulting in new magnetic interactions. The calculated results were improved northerly. This work will do some contributions to the anisotropy theory of HTS bulk and the present HTS Maglev system design.