Critical Current Densities of MOCVD Tapes for Different Current Directions

Abstract

The critical current density of an MOCVD/IBAD coated conductor was measured on tracks patterned longitudinally (L) and transversely (T) to the tape direction. Despite the samples' vicinality no dependence of on track direction was found for magnetic fields applied perpendicular to the film plane. In angular out-of-plane measurements the previously reported asymmetry due to tilted precipitate planes was observed in an L track, whereas curves from a T track were almost perfectly symmetric with similarly high absolute values of . At low fields the effects of surface pinning were seen. Our results show that in most scenarios the current carrying capability is equally as good parallel and perpendicular to the tape direction, which is highly relevant for ROEBEL cables. In measurements where the magnetic field was swept in the film plane the anisotropy was found to be significantly higher than for MOD/RABiTS samples, which we explain by the different morphology of grain boundaries in the tapes. At low temperatures of a T track exhibited a clear signature of vortex channeling.

Critical current anisotropy of GdBCO tapes grown on ISD–MgO buffered substrate

“…The vortex channeling minimum is smeared out in our samples by the grain-to-grain misalignment of the ab-planes. The same indication of vortex channeling suppression was also reported in MOCVD/IBAD tapes with meandering GBs [13]. The FF peak expected at θ = 90°was again dominated by the anisotropy between the H ab  and H c  and thus a smooth decrease was observed in the data around θ = 90°where the FF configuration is expected.…”

“…It manifests as a strong and local decrease of J c in its angular dependence when the Lorentz force drives cross-cutting and motion of the vortex strings along the planar defects. This effect has been reported in various materials such as vicinal YBCO films [11,12], MOCVD/IBAD CCs [13] and samples with planar grain boundaries [14,15] and twin boundaries [16].…”

Trapped fields up to 2 T in a 12 mm square stack of commercial superconducting tape using pulsed field magnetization

“…Flux creep also adds uncertainty to the definition of persistent current. Finally, the difference is not due to there being a lower J c perpendicular to the tape transport axis as the I c of the sample shown in figure 6 was measured to be 275 ± 10 A using a high current goniometer system [26] and in general perpendicular J c is not expected to be less for MOCVD Superpower tape [25]. The above discussion shows that care must be taken when relating the persistent current that can be induced in (RE)BCO tapes pieces to their transport critical current.…”

“…It is believed that the difference between these two values is because persistent current in a single layer generates a very different self-field pattern to transport current. Basic modelling shows that the self-field experienced by a tape carrying persistent current is on average higher in magnitude which can significantly reduce the apparent J c given the steep dependence on field at low field values [25]. The field lines are also in general more perpendicular to the tape surface for a persistent current which can also have a significant effect on J c [25].…”

“…Basic modelling shows that the self-field experienced by a tape carrying persistent current is on average higher in magnitude which can significantly reduce the apparent J c given the steep dependence on field at low field values [25]. The field lines are also in general more perpendicular to the tape surface for a persistent current which can also have a significant effect on J c [25]. Flux creep also adds uncertainty to the definition of persistent current.…”