AN INTERNAL-EXTERNAL BRONZE PROCESS FOR THE MANUFACTURE OF LARGE FILEMENT NB3SN

THERE HAS BEEN, FOR SOME YEARS, A NATIONAL NEED FOR A HIGHER QUALITY, HIGHER JC NB3SN THAN THAT DEVELOPED OVER 10 YEARS AGO AND USED IN THE LARGE VOLUME U.S. APPLICATIONS, I.E. WESTINGHOUSE LCP, HFTF, AND MIT 12T. IN RECENT MONTHS,BRONZE PROCESSED MATERIAL WITH PROPERTIES AT LEAST EQUAL, IFNOT SUPERIOR TO THOSE OF THE OTHER APPROACHES, HAS BEEN REPORTED FROM JAPAN; HOWEVER, THIS WAS IN VERY FINE FILAMENTMATERIAL. AT VERY HIGH FIELDS, THE EFFECTS OF PRESTRESS MAKE SUCH FINE FILAMENTS UNDESIRABLE. IT IS STILL NECESSARY, HOWEVER, TO HAVE HIGH INTERFACIAL AREA BETWEEN NBAND BRONZE TO INCREASE THE DIFFUSION RATES OF JC'S. THE SOLUTION TO THIS PROBLEM HAS BEEN TO USE TUBES OF NB AND TO HAVE THE TUBE PERFORM THE DUAL FUNCTIONS OF CONDUCTOR AND DIFFUSION BARRIER. THIS HAS MEANT EITHER POOR UTILIZATION OF THE NB OR, IF TOO MUCH OF THE NB WERE REACTED, BREAKTHROUGH OF SN AND STABILIZER CONTAMINATION. IN THIS PROPOSAL WE SUGGEST THAT THE TUBES PERFORM THE CONDUCTOR FUNCTION ONLY AND ARE COMPLETELY REACTED. BRONZE IS LOCATEDBOTH INSIDE AND OUTSIDE THE TUBES AND THE STABILIZER IS SEPARATED FROMT HE REST OF THE CONDUCTOR BY A SEPARATE TA OFV BARRIER AS IN THE EXTERNAL BRONZE PROCESS. IN THIS WAY A MUCH BETTER UTILIZATION OF THE NB WILL RESULT, GRAIN SIZE OF NB3SN WILL BE KEPT SMALL, AND THE PRESTRESS EFFECTS WILL BE MINIMAL. ADDITIVES SUCH AS TI, AND POSSIBLY, TA WILL BE EPMLOYED THROUGHOUT THIS WORK TO IMPROVE DIFFUSION RATES ANDJC AT HIGH FIELDS. CU BARRIERS WILL BE CONSIDERED TO IMPROVE THE TUBE UNIFORMITY AND SURFACE CONDITION.