SIMPLIFIED JOSEPHSON-JUNCTION ARRAYS AS MODELS OF GRANULAR SUPERCONDUCTORS

We describe the simplest Josephson junction array models that can be a dopted in studying the diamagnetic properties of granular superconduct ors. We consider cylindrical superconducting granular samples in the p resence of an axial external magnetic field H. The electrodynamic resp onse of these systems can be analyzed by means of three-dimensional (3 D) equivalent networks of Josephson junctions coupled through inductan ces. However, in the low field reversible regime a 2D Josephson juncti on array can be used. In order to study irreversible flux penetration in 3D systems, we give the equivalent network and qualitatively discus s the dynamics of flux penetration. We notice that, in analogy to 2D n etworks, First Irreversible Flux Penetration (FIFP) occurs when the va lue of the shielding current approaches the maximum Josephson current in the weakest external junction of the network.