Large and field-insensitive critical current densities in (Sr,Na)Fe2As2 superconducting tapes

We have fabricated (Sr,Na)Fe2As2 tapes by optimizing the sintering temperature and time, and characterized their transport J(c) at 4.2 K up to 14 T. The transport J(c) for the (Sr,Na)Fe2As2 tape sintered at 875 degrees C reaches 4.9 x 10(4) A/cm(2) under self-field, and it is suppressed only down to 1.9 x 10(4) A/cm(2) even at 14 T. We succeeded in fabricating very field-insensitive tapes, which are very promising for practical applications. We also report compositional distributions and magneto-optical images of current distribution in tapes. Magneto-optical imaging of the core of the tape clarified inhomogeneous intergranular current distributions.