Electromagnetic coupling in small grain YBa 2Cu 3O 7–δ superconducting ceramics: full and hollow cylinders

Abstract

This paper describes a method to assess the electromagnetic characteristics of a superconducting ceramic material. YBa 2Cu 3O 7– δ ceramic samples have been made in the form of hollow cylinders with the standard 4 terminal configuration for measurement of the critical current ( I c) attached to the outer surface. An additional wire carries a second internal current ( I int) along the central axis. I c can thus be modulated by I int. In particular, an increase in I c can be achieved by directing I int in the opposite direction to the cylinder current in order to compensate the self-generated magnetic field. The I c– I int characteristic can be described by a critical state model where we assume a linear dependence between the local critical current density ( j c) and the local magnetic field ( H) for the superconducting polycrystalline material. Based on this linear model the experimental data for a given sample can be analysed to extract two parameters: the maximum local critical current density ( j 0) and the local magnetic field ( H 0) for which j c should vanish. The best sample yielded j 0=1023 A cm –2 and H 0=4450 A m –1.