CHANGES IN NB3SN CONDUCTORS MADE BY THE "INTERNAL TIN" METHOD, TO IMPROVE MAGNET PERFORMANCE.

AS RESULT OF A DEVELOPMENT PROGRAM CARRIED OUT OVER A PERIOD OF MANY YEARS, IGC/ASI HAS BEEN ABLE TO PRODUCE "INTERNAL TIN" MATERIAL IN LONG PIECE LENGTHS WITH FILAMENTSOF A VARIETY OF DIFFERENT COMPOSITIONS. HOWEVER, A LACK OF CONFIDENCE IN THE ABILITY OF NB3SN TO PERFORM RELIABLY IN A RANGE OF DIFFERENT MAGNET DESIGNS EXISTS IN THE MINDS OF MANY MAGNET BUILDERS, MAKING IT VERY DIFFICULT TO COMMERCIALIZE THE PRODUCT. WHEN ANY MAGNET PERFORMS BADLY IT IS DIFFICULT TO DETERMINE WHETHER IT IS DUE TO DEFECTIVE WIRE OR THAT THE MATERIAL HAS BEEN HANDLED POORLY BY THE MAGNET WINDER. THIS IS PARTICULARLY TRUE OF A RELATIVELY BRITTLE MATERIAL SUCH AS REACTED NB3SN. THE AIM OF THIS PROPOSED WORK IS TO DEVELOP ACCEPTANCE FOR THE MATERIAL PRODUCED BY THE "INTERNAL TIN" PROCESS AS THE ECONOMICAL, RELIABLE, NB3SN MADE IN THE UNITED STATES, BY IMPROVING THE WIRE IN PHASE I AND MAKING COILS FROM THIS IMPROVED CONDUCTOR IN PHASE II. AT THE PRESENT TIME, SOME MAGNET WINDERS RELY ON AN OVERSEAS SUPPLIER WHOSE PRODUCT HAS A HIGHER COST AND LOWER PERFORMANCE CAPABILITY. THE SPECIFIC PURPOSE OF THIS PHASE I WORK IS TO EXAMINE THE UNIFORMITY OF THE TIN DISTRIBUTION IN THE MATERIAL AFTERHEAT TREATMENT, ALONG THE WIRE'S LENGTH AND ACROSS ANY CROSS SECTION. HOW THIS UNIFORMITY IS RELATED TO THE WIRE SIZE, THE CONDUCTOR DESIGN AND THE HEAT TREATMENT CONDITIONS WILL ALSO BE INVESTIGATED. THE OUTCOME OF THE PHASE I WORK WILL BE THE DETERMINATION OF THE SIGNIFICANCE OF SUCH A RECENTLY OBSERVED PHENOMENON AS THE LARGE VOID FORMATION IN THE TIN AREAS AFTER CERTAIN HEAT TREATMENT CYCLES. THESE VOIDS APPEAR TO BE LARGER THAN THOSE NORMALLY ASSOCIATED WITH THE "KIRKENDALL EFFECT" WHICH HAVE BEEN RECOGNIZED FOR SOME TIME. THEY APPEAR TO BE MORE IN THE NATURE OF MELTING CAVITIES. THIS PHASE I WORK WILL LEADTO IMPROVED CONDUCTOR DESIGNS, FABRICATING CONDITIONS AND HEAT TREATMENT PROCEDURES. IN THE PHASE II PART OF THE PROGRAM, THE ABOVE DEVELOPED DESIGNS WILL BE USED TO PRODUCE SEVERAL CONDUCTORS IN COMMERCIAL QUANTITIES AND WIND COILS TO DEMONSTRATE THE MATERIAL'S SUITABILITY FOR A RANGE OF DIFFERENT APPLICATIONSINCLUDING PERSISTENT MODE OPERATION. SOME OF THE CONDUCTOR DESIGNS ARE EXPECTED TO INVOLVE LARGER NUMBERS OF SUBELEMENTS WHICH WILL INTRODUCE GREATER BONDING PROBLEMS AND RESULT IN DECREASED PIECE LENGTHS. THE UNDERSTANDING OFTHESE BONDING PROBLEMS, PARTICULARLY AS THEY RELATE TO THE COMPOSITION AND HARDNESS OF THE SUBELEMENT ARRAYS WILL BE INVESTIGATED FURTHER IN PHASE II.