Double critical-state model for the weak-link regime of granular high-Tc superconductors

The phenomenological double critical-state model, which uses critical values for the components of the current-density both perpendicular and parallel to the local magnetic induction B, is applied to tubes of granular high-T-c superconductors in the presence of axial and azimuthal magnetic fields. We develop a theory valid for the weak-link regime of these superconductors. In this theory not only intergranular but also intragranular currents are taken into account. The behavior of the magnetic induction inside the wall of a superconducting tube cooled below the critical temperature in the axial magnetic field and, later, subjected to an increasing azimuthal field, is analyzed. Our theoretical results are compared with the experiment. (C) 1998 Elsevier Science B.V.