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 Nh filament size and heat treatment cycle. Various heat treatments were applied to Nb3Sn 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.