METHODS OF IMPROVING INTERNAL-TIN NIOBIUM-TIN FOR FUSION APPLICATIONS

IT HAS BEEN REPORTED THAT, WHEN A TIN BRONZE CONTAINING A SMALL PERCENTAGE OF GERMANIUM IS USED TO REPLACE THE NORMAL TIN BRONZE AS THE MATRIX IN THE BRONZE PROCESS FOR THE MANUFACTURE OF NIOBIUM-TIN (NB3SN), THE CRITICAL CURRENT (JC) IS INCREASED BY A FACTOR OF TEN IN THE FIELD RANGE 8 TO 16 T. THIS PROJECT WILL COMPARE THE JC PROPERTIES OF INTERNAL-TIN NB3SN MADE FROM A MATRIX CONTAINING A SMALL QUANTITY OF GERMANIUM WITH THOSE FROM A MATERIAL WITH A PURE COPPER MATRIX. SINCE THE PRINCIPAL NEED IS TO INCREASE THE JC IN THE HIGHER FIELD REGION, THE EFFECT ON MATERIAL WITH NB 7.5 WEIGHT % TANTALUM (TA) AND NB 1 WEIGHT % TA AS WELL AS PURE NB FILAMENTS WILL BE EXAMINED. IN PHASE I, TRIAL BILLETS WILL BE PREPARED FROM MATERIAL WITH A PURE COPPER MATRIX TO PROVIDE BASELINE COMPARISONS. THE PRINCIPAL INVESTIGATION WILL BE CARRIED OUT ON BILLETS WITH COPPER GERMANIUM MATRICES AND THE THREE FILAMENT COMPOSITIONS MENTIONED ABOVE. THE RATE OF STRAIN HARDENING OF ALLOYED MATRICES IS EXPECTED TO BE HIGHER THAN THAT OF PURE COPPER AND, IN THE PAST, PROBLEMS HAVE BEEN ENCOUNTERED WHEN ATTEMPTS WERE MADE TO COLD BOND HARD SUBELEMENTS IN THE TIN-CORE PROCESS. THE TUBULAR-TIN-SOURCE (TTS) PROCESS, HAS BEEN SHOWN TO BE FAR LESS SENSITIVE TO THE HARDNESS OF THE MATRIX WHEN A HOT ISOSTATIC PRESSING STEP IS USED IN THE PROCESSING OF THE CORE. THE TTS PROCESS HAS, THEREFORE BEEN CHOSEN FOR THIS PRELIMINARY WORK, BUT PHASE II WILL INVESTIGATE THE SUITABILITY OF GERMANIUM ALLOYED MATRICES FOR THE TIN-CORE NB3SN PROCESS.