Heat Treatment Optimization Studies on PIT Nb3Sn Strand for the NED Project

For the Next European Dipole (NED) program, a Powder-In-Tube (PIT) strand was successfully developed by SMI. This high-performance Nb3Sn strand presents a non-copper critical current density of similar to 2500 A/mm(2) at 12 T applied field and 4.2 K and a filament diameter around 50 mu m. Extensive heat treatment optimization studies were performed in order to maximize both critical current and RRR, with a plateau temperature down to 625 degrees C and duration up to 400 hours. It appears that a critical current enhancement of similar to 10% can be achieved for a reaction schedule of 320 hours at 625 degrees C with non-copper critical current density respectively exceeding 2700 and 1500 A/mm(2) at 12 and 15 T (4.2 K). Thanks to this modified heat treatment, this strand completely fulfills the NED stringent specification.