Study of coupling loss on bi-columnar BSCCO/Ag tapes by a.c. susceptibility measurements

TL;DR

This study investigates coupling losses in bi-columnar BSCCO/Ag superconducting tapes using a.c. susceptibility measurements, analyzing how matrix composition and sample length affect electromagnetic losses and flux dynamics at 77 K.

Contribution

It introduces a detailed analysis of coupling losses in bi-columnar superconducting tapes with different matrices, applying a theoretical model to determine effective resistivity from experimental data.

Findings

Losses match theoretical models for round multifilamentary wires.

Effective resistivity varies with matrix composition, showing discrepancies explained by interface properties.

Sample length influences magnetic flux penetration and coupling behavior.

Abstract

Coupling losses were studied in composite tapes containing superconducting material in the form of two separate stacks of densely packed filaments embedded in a metallic matrix of Ag or Ag alloy. This kind of sample geometry is quite favorable for studying the coupling currents and in particular the role of superconducting bridges between filaments. By using a.c. susceptibility technique, the electromagnetic losses as function of a.c. magnetic field amplitude and frequency were measured at the temperature T = 77 K for two tapes with different matrix composition. The length of samples was varied by subsequent cutting in order to investigate its influence on the dynamics of magnetic flux penetration. The geometrical factor $\chi_0$ which takes into account the demagnetizing effects was established from a.c. susceptibility data at low amplitudes. Losses vs frequency dependencies have been found to agree nicely with the theoretical model developed for round multifilamentary wires. Applying this model, the effective resistivity of the matrix was determined for each tape, by using only measured quantities. For the tape with pure silver matrix its value was found to be larger than what predicted by the theory for given metal resistivity and filamentary architecture. On the contrary, in the sample with a Ag/Mg alloy matrix, an effective resistivity much lower than expected was determined. We explain these discrepancies by taking into account the properties of the electrical contact of the interface between the superconducting filaments and the normal matrix. In the case of soft matrix of pure Ag, this is of poor quality, while the properties of alloy matrix seem to provoke an extensive creation of intergrowths which can be actually observed in this kind of samples.