Direct identification of extended defects as vortex pinning centers in melt textured YBa2Cu3O7-Y2BaCuO5 composites

Single domain YBa2Cu3O7-Y2BaCuO5 melt textured ceramic composites have revealed a very rich microstructure, which has usually impeded, by using standard measurements, to evaluate the contribution of each defect to the enhancement of the critical current. We have measured the inplane magnetoresistance anisotropy and the anisotropic in-plane inductive critical currents and we show that together with the microstructural TEM analysis, the contribution of the different extended pinning centers can be separated. These results have allowed us to infer the kind of microstructure modifications required to improve the critical current. In particular, we present an isostatic pressing deformation technique as a very promising post-processing treatment to strongly increase the critical currents of these composites.Peer Reviewe

Current distribution in HTSC tapes obtained by inverse problem calculation

The development of SC devices based on HTSC tapes requires a deep knowledge of the current distribution in both pre-saturation and post-saturation regimes. Magnetic measurements have shown the possibilities to derive the current distribution by Inverse Problem Solution in finite sized bulks, based on a non destructive measurement of the magnetic field created by the own current flowing in the SC. In this work, the QR inversion strategy is extended to non finite systems by considering the effect of the boundaries. We present a method to derive the current distribution in a cross-section of a tape based on Hall magnetic mapping by using a specifically designed inverse problem solver. This method is applied to a series of Hall measurements corresponding to a full magnetization cycle of a commercial tape, produced by applying a set of the currents applied to the tape of several intensities. Details of the experiments and the calculation method are reported and the applicability as homogeneity test and losses studies is discussed.Peer ReviewedPostprint (published version

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

High-temperature superconducting artificially structured bulk samples, such as bulks with slanted drills or welds of different pieces along the c-axis with holes drilled in different asymmetric positions, pose a challenge for the computation of critical current maps able to spot the position of inhomogeneities, as they combine a current map in every ab-plane adapted to the drill/welding structure with the dependence of this structure on the position along the c-axis. We improve and adapt our technique of Hall probe field measurement, discretization and QR inversion to this problem by measuring the magnetic field on top and bottom of the bulk sample to obtain some spatial resolution of the current. To test our technique we apply it to both simulations with asymmetrical geometry and a real artificially structured bulk samples.Peer ReviewedPostprint (published version