ATTEMPTS TO REDUCE A.C. LOSSES IN HIGH CURRENT DENSITY INTERNAL-TIN NB3SN

High current density designs of internal-tin Nb3Sn employing a single barrier to separate the superconductor from the stabilizer have proved to be unstable at the desired sizes in some short sample tests. Bridging between subelements occurs and the effective filament diameter (d(eff)) is considerably greater than the value of < 40 mum specified by the High Energy Physics (HEP) community. In this investigation we have explored the extent to which the other properties are changed when the losses are decreased by using multiple barriers to ensure the separation of the subelements. The effect of internal fins, of the type used in the Mono Element Internal Tin (MEIT) process [1], on the values for critical current density (J(c)) and d(eff) of multiple barrier restacks, is also reported, as are some problems encountered by the addition of Ti and possibly Cu to the Sn core.