Heat treatment optimization of internal tin Nb3Sn strands

The development of high critical current density (J_c) multifilamentary Nb₃Sn strands with low magnetization is important for many technological applications, including construction of high field accelerator magnets. To achieve this goal, strand R&D is actively pursued by Fermilab and IGC using the internal tin process. The J_c of a Nb₃Sn strand made with the internal tin technology depends on numerous factors, including Nb filament size and heat treatment cycle. Various heat treatments were applied to Nb₃ Sn strands of different designs produced by IGC. The effect of filament size was studied both during the Nb₃Sn layer growth and after complete reaction. The resulting J_c´s are presented, as well as SEM microscopy of strand sections