Vortex dynamics in bulk HTS with levitation techniques

Abstract

We have developed a set of experimental techniques with levitation to investigate the macroscopic magnetic properties of bulk HTS: (i) resonance oscillation technique; (ii) high speed magnetic rotor technique; (iii) the method of viscous motion of a permanent magnet through a HTS aperture under a steady force. Early, we used these techniques to investigate the magnetic flux dynamics in granular HTS. Now, we have extended and modified these techniques to study the large grain melt-textured HTS. With resonance oscillations technique we obtain the energy losses vs ac magnetic field amplitude at HTS surface and can derive the values of critical current density with high accuracy. We extract information about distribution of critical current in a thin undersurface layer and, in this way, check the HTS degradation processes. The treatment of the HTS surface that has influence on the surface pinning was investigated with this technique.