Fabrication and properties of monofilamentary MgB₂ superconducting tapes

Nickel-sheathed MgB₂ tapes were fabricated by means of the powder-in-tube method with a monocore configuration of the superconductor. The metallic tubes were filled with commercial reacted powders and cold-worked, respectively, by groove rolling, drawing, and rolling to flat tapes of about 4 mm in width and 0.35 mm in thickness. Portions of the manufactured conductors were heat-treated in an argon atmosphere at temperatures up to 940 °C. Conductors were characterized by transport measurements to determine the magnetic field dependence of the critical current density, the irreversibility line, as well as to establish an initial relationship between the thermo-mechanical treatment and the current carrying capacity of the manufactured MgB₂ samples. Our optimized samples for the low field operation carry a critical current density of at least 4 × 10⁵ A cm⁻² at 4.2 K, 1 T. The main outcome of this study, however, is that the optimal heat treatment condition changes if the MgB₂ conductor has to be employed respectively for a low- or high-field operation. Finally, the first successful demonstration of the current carrying capability of longer MgB₂ tapes is also reported in this paper.