Magnetic flux diffusion through HTS shields

Abstract

Slow field leakage in a polycrystalline superconducting cupshield placed in an external axial field (H-ext) much weaker than H-C1 shows a diffusive time dependence with a time scale of 10(2) s. As the field strength increases but is still less than H-C1, a logarithmic time dependence of 10(2) s time scale is observed. It is shown that this logarithmic time dependence is a result of flux line diffusion between superconducting grains rather than fluxoid avalanches or flux bundle creep.