Transport currents measured in ring samples: test of superconducting weld

The critical current densities in bulk melt-textured YBa2Cu3Ox and across s uperconducting "weld" joints are measured using scanning Hall probe measure ments of the trapped magnetic field in ring samples. With this method, crit ical current densities are obtained without the use of electrical contacts. Large persistent currents are induced in ring samples at 77 K, after cooli ng in a 3 kG field. These currents can be determined from the magnetic fiel d they produce. At 77 K a supercurrent exceeding 2000 A (about 10(4) A/cm(2 )) was induced in a 2 cm diameter ring; this current produces a magnetic fi eld exceeding 1.5 kG in the bore of the ring. We demonstrate that when a ri ng is cut, and the cut is repaired by a superconducting weld, the weld join t can transmit the same high supercurrent as the bulk. (C) 2001 Elsevier Sc ience B.V. All rights reserved.