Determination of the inter- and intra-granular critical currents in superconducting YBa₂Cu₃O₇welds

Abstract

A method for determining simultaneously the inter-and intra-grain critical currents has been developed in welded YBa 2 Cu 3 O 7 (YBCO) ceramics by solving the Inverse Problem for local maps of the magnetic field in the remanent state. From that current distribution, the current density flowing through the superconducting weld as well as the current density circulating inside the grains can be deduced. The method is discussed and it is applied to several examples of YBCO/Ag/YBCO welds. The results obtained show that it is possible to obtain superconducting joints with a quality at the same level as that of the starting material.

Effective silver-assisted welding of YBCO blocks: mechanical versus electrical properties

“…Finally, we studied the relation between the electrical and mechanical performance of YBCO silver welds, the later described in terms of the ratio H GB /H G between the minimum nanohardness value at the weld region and that of the grains. The intergrain-to-intragranular critical current density of each weld, J GB c /J G c , was determined from the magnetic field distribution B z (x, y) at 77 K, in the remanence (see, e.g., figure 6), following the procedure already described in [23].…”

“…A magnetic Hall probe scanning system with 160 μm spatial resolution was used to determine B z (x, y) maps of the ab plane of welds in the remanence at 77 K. Details of the system can be found elsewhere [20][21][22]. The grain and intergrain critical current densities, J G c and J GB c , were simultaneously determined from inversion of the measured B z map, following the methodology described in [23,24].…”

Detection of Current Distribution in Bulk Samples With Artificial Defects From Inversion of Hall Magnetic Maps

“…The authors have adapted in [4], [6] the discretization procedure of [2] to both HTS thin films and bulk samples, with the above hypotheses (a) and (b) as the only regularity assumptions made on the critical current in the sample, and are able to obtain from measurements of the vertical magnetic field above the sample a 2-dimensional map of the critical current , with a resolution comparable to that of the magnetic measurement, detecting irregularities such as multiple domains or welds [8], [9]. The discretized Biot-Savart problem is solved by an over-determined QR inversion to achieve results that are robust in front of measurement errors.…”

Computation of critical current in artificially structurated bulk samples from Hall measurements

“…In the latter case the above hypotheses (a) and (b) were the only regularity assumptions made in order to determine the critical current on the sample. The algorithm of linearization and QR-inversion is thus able to detect irregularities such as multiple domains or weldings [5,6], but doubts have lingered about the meaning of the results of this computation in bulk samples [7]. We begin by establishing the limit to the computability of critical currents in bulk samples from magnetic field measurements.…”