Novel, internally stranded Bi cuprate conductor concept for ac applications: ring-bundled barrier (RBB) tapes produced by the powder-in-tube assembleand react (PITAR) method

Novel, ring-bundled barrier (RBB) Bi-2223 tapes for high-current ac applica tions are prepared by the new powder-in-tube assemble and react route (PITA R), where multifilament wires are bundled around a central SrCO3 core withi n an outermost tube. Wire twisting, rolling and thermomechanical reaction l eads to a tape similar to the common Rutherford cable. PITAR avoids the lim itations of assembling the too stress-sensitive, reacted Bi-2223 tapes. App lying standard tape deformation routes and reaction parameters, critical-cu rrent densities of the order of 0.5-1 kA cm(-2) are achieved. Size-scalabil ity is demonstrated by preparing tapes of various filament/strand configura tions with comparable critical current densities. Ag98Mg2-alloy outer sheat hing enlarges the tape's tensile stress up to 160 MPa at 77 K. Dc magnetic- field and angular dependences of transport current densities at 77 K indica te a texture quality slightly below standard tapes, due to the mechanical b ehaviour of the SrCO3 barrier. Magneto-optical images confirm a successful realization of the conductor concept and indicate a homogeneous current dis tribution on the critical-current density level reached so far. Twist pitch es of 95 mm, 47 mm and 23 mm do not systematically degrade the critical cur rent density, yet a clear strand-decoupling is observed in external, perpen dicular ac fields. This demonstrates the possibilities inherent to the cond uctor design with regard to future ac application.