Electromagnetic coupling in small grain YBa2Cu3O7-delta superconducting ceramics: full and hollow cylinders

This paper describes a method to assess the electromagnetic characteristics of a superconducting ceramic material. YBa2Cu3O7-delta ceramic samples hav e been made in the form of hollow cylinders with the standard 4 terminal co nfiguration for measurement of the critical current (I-c) attached to the o uter 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 direc tion to the cylinder current in order to compensate the self-generated magn etic field. The I-c-I-int characteristic can be described by a critical sta te model where we assume a linear dependence between the local critical cur rent density (j(c)) and the local magnetic field (H) for the superconductin g polycrystalline material. Based on this linear model the experimental dat a 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) f or which j(c) should vanish. The best sample yielded j(0) = 1023 A cm(-2) a nd H-0 = 4450 A m(-1). (C) 2001 Elsevier Science B.V. All rights reserved.