Novel, internally stranded Bi cuprate conductor concept for acapplications: ring-bundled barrier (RBB) tapes produced by the powder-in-tubeassemble and react (PITAR) method

Abstract

Novel, ring-bundled barrier (RBB) Bi-2223 tapes for high-current acapplications are prepared by the new powder-in-tube assemble and react route(PITAR), where multifilament wires are bundled around a central SrCO3core within an outermost tube. Wire twisting, rolling and thermomechanicalreaction leads to a tape similar to the common Rutherford cable. PITAR avoidsthe limitations of assembling the too stress-sensitive, reacted Bi-2223 tapes.Applying standard tape deformation routes and reaction parameters,critical-current densities of the order of 0.5-1 kA cm-2 areachieved. Size-scalability is demonstrated by preparing tapes of variousfilament/strand configurations with comparable critical current densities.Ag98Mg2-alloy outer sheathing enlarges the tape's tensilestress up to 160 MPa at 77 K. Dc magnetic-field and angular dependences oftransport current densities at 77 K indicate a texture quality slightly belowstandard tapes, due to the mechanical behaviour of the SrCO3 barrier.Magneto-optical images confirm a successful realization of the conductorconcept and indicate a homogeneous current distribution on thecritical-current density level reached so far. Twist pitches of 95 mm, 47 mmand 23 mm do not systematically degrade the critical current density, yet aclear strand-decoupling is observed in external, perpendicular ac fields. Thisdemonstrates the possibilities inherent to the conductor design with regard tofuture ac application.