Electromagnetic coupling in small grain YBa2Cu3O7–δ superconducting ceramics: full and hollow cylinders

Abstract This paper describes a method to assess the electromagnetic characteristics of a superconducting ceramic material. YBa 2 Cu 3 O 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 .