Possible Reasons of Lorentz Force Direction Influence on Anisotropy of 2G HTS Tapes Critical Currents

Progressive advance in technology of second-generation (2G) high-temperature superconducting (HTS) superconductors leads to the continuous rise of their critical-current density. Critical current of 200 A at 4-mm tapes and ~600 A at 12-mm tapes is already state of the art. One problem is that critical currents of HTS tapes have sounding anisotropy. Moreover, it was found that in external magnetic field, the Lorentz force direction is affecting the critical currents of 2G HTS tapes. Two hypotheses were suggested as a reason for this phenomenon. This is the result of the properties of crystal lattice in a 2G HTS tape or of spatial inhomogeneity of critical currents across the width of HTS tapes. In this paper, the verification of hypotheses was done by the cutting of wide 2G HTS tapes into narrow tapes and measuring of critical-current anisotropy in narrowed tapes. We present the experimental results and their discussion. We concluded that the spatial inhomogeneity of critical-current density in the cross section of a tape is the reason for the Lorentz force direction influence on the anisotropy of 2G HTS tape critical currents.