Fabrication and superconducting properties of powder-in-tube processed MgB_2 tapes

摘要

The powder-in-tube process has been employed to fabricate long nickel-sheathed MgB_2 superconducting tapes from reacted commercially available powders. We have found that reacted MgB_2 powders reach a high degree of density inside the nickel sheath during the cold working procedure and, thanks to the large superconducting coherence length, a considerable current flow is therefore achievable even without sintering. At 4.2 K and self-field, a transport current density value j_c of 10~5 A/cm~2 has been indeed reached over long portions of unsintered monofilamentary tapes. The irreversibility lines both for a magnetic field oriented parallel and perpendicular to the MgB_2 superconducting tape have been determined by magnetoresistance measurements. These data are consistent with a slight texturing process of the MgB_2 grains occurring during the cold working procedure.