ECONOMICAL AND RELIABLE NIOBIUM-TIN CONDUCTORS VIA INNOVATIONS IN STABILIZERS

HIGH CRITICAL CURRENT DENSITIES (JC) AND LOW AC LOSSES ARE BEING ACHIEVED IN NB3SN AS A RESULT OF DESIGN AND/OR PROCESS INNOVATIONS THAT CAME ABOUT OVER THE LAST DECADE. THE SO-CALLED INTERNAL TIN APPROACH WHICH HAS BEEN THE CHOICE OF US INDUSTRY, HAS EMERGED IN MANY FORMS; EACH WITH A NOVELTY TO ADDRESS ONE CHARACTERISTIC OF THE CONDUCTOR OR ANOTHER. THE GENERAL APPROACH ITSELF INVOLVES THE MANUFACTURE OF TWO MAJOR COMPONENTS - 1) A COMPOSITE ELEMENT AND 2) A STABILIZER TUBE. THE LATTER PROVIDES RELATIVELY LARGE AMOUNTS OF COPPER DESIRABLE IN THE WIRE TO ADD STABILITY AND PROTECTION TO THE FINAL SUPERCONDUCTING DEVICE. IT HAS TO INCORPORATE DIFFUSION BARRIERS SUCH AS NB, TA, OR V TO KEEP THE TIN FROM POLLUTING THE COPPER DURING FINAL HEAT TREATMENT. IN CASES OF PULSED FIELD APPLICATIONS, IT SHOULD NOT REACT WITH TIN FORMING A CONTINUOUS A15 SUPERCONDUCTING LAYER. THE PRESENT METHOD OF MAKING THE STABILIZER MEMBER IS BY TUBULAR HOT EXTRUSION. THE GEOMETRY AND DUCTILITY CONSTRAINTS PLACED ON THE DIFFUSION BARRIER MATRIAL ARE SO DEMANDING THAT OVER THE YEARS THE STABILIZER MANUFACTURING PROCESS HAS BECOME A VERY EXPENSIVE AND TEDIOUS ONE. IN ORDER TO LIMIT TOTAL STRAIN FROM BILLET TO FINAL WIRE, THE STABILIZER BILLET DIAMETER AND THE RESTACK BUNDLE SIZE HAVE BEEN REDUCED RAISING THE COST MATERIALS. SINCE THE STABILIZER IS A CRITICAL COMPONENT BOTH IN TERMS OF PRODUCT PERFORMANCE AND COST, IGC ADVANCED SUPERCONDUCTORS PROPOSES A PROGRAM TO DEVELOP RELIABLE AND SIGNIFICANTLY ECONOMICAL NB3SN CONDUCTORS BY IMPROVING STABILIZERS. THE FEASIBILITY OF PRODUCING STABILIZERS BY HOT ISOSTATIC PRESSING (HIP), TOTALLY CIRCUMVENTING EXTRUSION WILL BE STUDIED IN PHASE I. BARRIER MATERIALS-NB, TA, AND A COMBINATION OF THE TWO WILL BE INCORPORATED IN SMALL STABILIZERS WHICH WILL BE FURTHER TESTED BY CO-DRAWING WITH COMPOSITE MATERIALS. MECHANICAL AND MATERIAL DESIGN DETAILS AND HIP PARAMETERS THAT ARE OPTIMAL WILL BE INVESTIGATED. FOLLOWING THE SUCCESS OF PHASE I EFFORT, SCALED-UP DESIGNS AND COST DETAILS FOR LARGE QUANTITY PRODUCTION WILL BE ADDRESSED.