THE INVESTIGATION OF AN IMPROVED PROCESSING METHOD FOR HIGH CURRENT DENSITY, FINE-FILAMENTARY SUPERCONDUCTORS-

THE PRESENT INTEREST IN NBTI COMPOSITE CONDUCTORS WITH VERY FINE FILAMENTS HAS DEVELOPED BECAUSE SUCH MATERIAL IN THE SUPERCONDUCTING SUPER COLLIDER (SSC) IS NEEDED. IT IS NOW POSSIBLE TO PRODUCE MATERIAL, AT LEAST ON A SMALL SCALE, WITH NBTI FILAMENTS 2.5UM IN DIAMETER, WHICH EXHIBITS >2500 A/MM AT 5T AND 4.2 'K. THE PROBLEM IS TO PRODUCE SUCH A MATERIAL, WHICH MAY CONTAIN >20,000 FILAMENTS, IN THE MOST ECONOMICAL WAY POSSIBLE. THE LARGE NUMBER OF MAGNETS INVOLVED IN THE SSC MAKES EVEN SMALL SAVINGS IN THE MATERIAL VERY VALUABLE IN THE OVERALL COST OF THE MACHINE ONE WAY TO ACHIEVE THE DESIRED PROPERTIES IS TO HYDROSTATICALLY EXTRUDE AT LOW TEMPERATURES, BUT UNFORTUNATELY NO LARGE HYDROSTATIC EXTRUSION PRESS EXSTS INT EXISTS IN THE UNITED STATES. ALSO THE VOLUME OF MATERIAL THAT CAN BE PROCESSED BY THE LARGES PRESENT-DAY HYDROSTATIC PRESS IN A SINGLE OPERATION IS SMALLER, AND THE PROCESSING COSTS HIGHER, THAN WHEN CONVENTIONAL EXTRUSION PRESSES ARE USED. CONVERSION OF EXISTING CONVENTINAL PRESSES TO HYDROSTATIC O OPERATION IS DIFFICULT AND EXPENSIVE. THIS INVESTIGATIN INVESTIGATION IS TO MODIFY THE BILLET PREHEATING CYCLE AND THE BILLET DESIGN TO CAUSE THE MATERA THE BILLET DESIGN TO CAUSE THE MATERIAL TO EXPERIENCE CONDITIONS SIMILAR TO THOSE EXISTING IN LOW TEMPERATURE HYDROSTATIC EXTRUSION. THIS WILL BE DONE BY RAPIDLY PREHEATING THE BILLET AND BY THERMALLY INSULATING THE OUTER COPPER PORTION FROM A THIN-WALLED INNER CAN CONTAINING THE NBTI FILAMENTS DURING THIS PREHEATING. IT WILL THEN BE POSSIBLE TO RAISE THE TEMPERATURE OF THE OUTER PORTION OF THE ABOVE THE CORE AND ENABLE THE FORMER TO ACT AS A PSUEDO-HYDROSTATIC MEDIUM. PRECOMPACTION ALSO IS USED WHEN VERY LARGE NUMBERS OF FILAMENTS AND HIGH CURRENT DENSITIES ARE REEQUIRED. THIS PRECOMPACTION IS NORMALLY DONE IN A SEPARATEE OPERATION, BUT IN THIS PROPOSAL THE BILLET IS DESIGNED SO THAT THE OPERATION CAN BE ACCOMPLISHED IN THE EXTRUSION PRESS LINER IMMEDIATELY BEFORE THE BILLET IS EXTRUDED. THUS, THE QUALITY OF THE PRODUCT WILL BE MAINTAINED BY LOW-TEMPERATURE, PSEUDO-HYDROSTATIC PROCESSING, AND THE COST WILL BE REDUCED IN TWO WYS^ (1) BY MAINTAINING LARGE BILLET VOLUME, AND (2) BY SIMULTANEOUSLY PRECOMPACTING AND EXTRUDING.