High Superconductor Fraction, High Engineering Critical Current Density Bi-2212/Ag Wires Fabricated by Ultrasonic Wire Drawing

75954-Recent work has shown that Bi:2212/Ag superconducting multifilament wires can be successfully used to wind Rutherford cables for particle collider magnets, but the engineering (overall) current density needs to be improved. Although the critical current density in the superconducting filaments is quite high, the presence of a large amount of Ag or Ag alloy in the composite (needed for mechanical strength during the drawing process) limits the engineering current density. Attempts to draw composites with higher filling factor (e.g., lower amounts of Ag or Ag alloy) have either failed or, when drawn with using techniques to reduce the drawing force, have led to wires with heavily distorted filaments. This project will develop a new technique for drawing wires with lower amounts of Ag or Ag alloy, in which ultrasonic vibrations are applied to the wire drawing die, permitting very large reductions (by a factor as high as seven) in the drawing force without distortion. The lower Ag or Ag alloy content increases the superconductor fraction and hence the engineering current density. In Phase I, an optimized set of dies will be built for ultrasonic drawing of Bi:2212/Ag wires. Three billets with different superconductor fractions will be assembled and drawn, both with conventional drawing and ultrasonic drawing. After heat treatment, short samples of wires will be characterized in terms of filament uniformity, superconducting properties, and mechanical properties. Commercial Applications and Other Benefits as described by the awardee: Bi:2212/Ag wires with high critical currents in high magnetic fields should enable particle collider superconducting magnets to generate fields in excess of 20T, increasing the attainable energy or reducing the size (and consequently the cost) of future particle colliders. The technology also could be used to upgrades to existing colliders, such as those at Fermilab and CERN.