High transport critical current density obtained for powder-in-tube-processed MgB2 tapes and wires using stainless steel and Cu–Ni tubes

MgB 2 tapes and wires were fabricated by the powder-in-tube method. Stainless steel and Cu–Ni tubes were used as sheath materials, and no heat treatment was applied. The tapes made of stainless steel showed transport critical current density Jc of about 10 000 A/cm2 at 4.2 K and 5 T. A high Jc of about 300 000 A/cm2 was obtained by extrapolating the Jc–B curves to zero field. Multifilamentary (seven-core) MgB2 wire was successfully fabricated using Cu–Ni tubes. For both tapes and wires, the grain connectivity of MgB2 was as good as a high-pressure sintered bulk sample. However, the Jc of the Cu–Ni sheathed wire was lower than the stainless steel sheathed tape due to the lower packing density of MgB2.