Three-dimensional field measurements of levitated HTS and the modeling of the shielding current

We developed a shielding current distribution model in a bulk superconductor with the aim of estimating the levitation force. First, we directly measured the magnetic field in axial and radial directions above a bulk Y-Ba-Cu-O superconductor levitated by an electromagnet using a three-dimensional Hall sensor. We then calculated the field distribution by assuming two types of the shielding current distributions and compared the results with the measured values. The field distributions based on the model in that the shielding currents are flowing concentrically at the surface were not in good agreement with the measured data. We then assumed that the shielding currents are not uniform and the boundary has the form of nth hyperbola, which could reproduce the measured field distribution reasonably well.