Abstract
High Tc melt-processed YBaCuO bulk superconductors have been utilized for the development of high Tc superconducting magnetic flywheel and bearing. In such systems, the superconductors suffer an A.C. magnetic field with frequencies of from tens Hz through several kHz during the rotation of a rotor where permanent magnet rings are installed. The A.C. magnetic field is caused by the inhomogeneity of the magnetic field generated by the magnet in the azimuthal direction. Here, the decay of a rotational speed induced by the A.C. magnetic field, termed rotational loss, becomes one of the most serious technical problems. We analyzed the A.C. magnetic properties of high Tc superconductors in the above frequency range using a fundamental experiment and numerical simulation based on the flux flow·creep model and the vortex-liquid model. Finally, we elucidate that the motion of the fluxoids and the resultant energy dissipation is dominant in the rotational loss.
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