Development of MgB2 New Superconducting Tapes and Wires

Abstract

We fabricated MgB2 tapes and wires by a powder-in-tube (PIT) method, using MgB2 powder and several sheath materials such as Cu, Cu-Ni, Ni, pure Fe, carbon steel (Fe-C), and stainless steel. Jc of the as-cold rolled (un-sintered) tape significantly increased with the increase of total cross-sectional area reduction by the cold working. Hard sheath materials such as Fe-C and stainless steel are effective to enhance the packing density of MgB2 core and, therefore, to increase Jc values. Non heat treated MgB2 tapes with Fe-C and stainless steel sheaths showed extrapolated Jc values of-3.0-4.5×109A/m2 at 4.2K and zero field. Heat treatment after the cold rolling is effective to enhance Jc values. An order of magnitude higher Jc values were obtained for Fe, Fe-C, and stainless steel sheathed tapes after the heat treatment. Extrapolated Jc values well above 1010A/m2 at 4.2K and a zero magnetic field were obtained for stainless steel and Fe-C sheathed MgB2 tapes. Jc values of PIT-processed MgB2 tapes are less sensitive to strain than those of PIT-processed Bi-based oxide tapes. It is reported that the addition of soft metal powder such as In or Sn to the MgB2 powder is effective to enhance Jc values. We made -10m-long tapes with Ni sheaths, and fabricated small solenoid coil with this tape without sintering. The Ic of the coil was about 80% of the Ic of the short tape, indicating that the homogeneity of Ic in the 10m tape is fairly good. The coil generated 1.3kGauss at 4.2K.