C-axis critical current density of second-generation YBCO tapes

We report on measurements of the temperature and field dependence of the c-axis critical current density (Jcc) obtained on mesa structures that were patterned into the YBCO layer of second-generation HTS tapes. We find the Jcc-values of ∼ 4 kA cm-2 at 77 K and self-field, corresponding to an unexpectedly high anisotropy in the critical current density Jcab/Jcc of 500-600. C-axis current flow is expected to arise in applications such as the helically wound wires in HTS cables. A simple estimate is given of the fraction of tape width for such a c-axis flow; while in our samples this fraction is approximately 5% for a typical geometry, the fraction will grow linearly with increasing current density anisotropy and could affect the current-carrying ability of the tape.