Ag-sheath magnetoresistance anisotropy in Bi(2223)/Ag multifilamentary tapes at 4.2 K

Abstract

The magnetoresistance of three different pure Ag, respectively BSCCO/Ag, tapes was examined. Further, the voltage-current characteristics of two 19-filament Bi(2223)/Ag short samples differing by current carrying capability were measured at 4.2 K in magnetic fields up to 10 T. The voltage-current characteristics were used to evaluate the differential resistance in the resistive regime as a function of current. The saturated value of the differential resistance was determined by extrapolation to relatively high currents and it was considered as the apparent silver sheath resistance. It showed a very low value in spite of various technological steps during preparation. It agreed well with the calculated value using the resistivity of the long-time heat treated pure Ag sample. The magnetic field-induced increase in resistance calculated in this way was lower than that, or approximately equal to that, measured in the transverse position with the broad face parallel with the magnetic field and/or in the longitudinal position. In contrast, in the transverse position with the broad face perpendicular to the magnetic field, the magnetoresistance was higher than the calculated one. The observed anisotropy ratio of the apparent silver sheath magnetoresistance was close to 2. Some mechanisms that could be responsible for such behaviour are discussed.

A numerical model for stability considerations in HTS magnets

“…Differences in the thermal conductivity, specific heat, and electrical conductivity between the samples-caused by porosity, grain alignment, oxygen stoichiometry and the multi-phase nature of the HTS material [47,48], defects in the matrix metal [49][50][51] and thermal boundary resistance between components [52]-may induce considerable errors into stability considerations. Therefore, while the thermal and electrical conductivities measured for pure silver are too optimistic for stability considerations, the properties measured on an Ag sample with ρ(4.2 K) = 0.3 n m are suggested to be more relevant [49].…”

Current and voltage distribution in composite superconductors with resistive barriers - symmetric case

“…Due to the inhomogeneity of the core material, this assumption is not always valid and the voltage on the normal matrix may not truly reflect the processes in the superconducting core. The meandering of current between the matrix and the core as treated in [5,6], can lead to curious effects such as, for example, the apparent anisotropy of the magnetoresistance of the silver matrix in BSCCO/Ag conductors referred to in [7].…”