Development of Internal-Tin Nb/Sn Strand for High Field Accelerator Dipole

72192-Future high field (15+T) dipole magnets will require superconductors with high current density and lower costs. This project will develop technology for lowering the cost of the Nb/Cu filaments that go into the internal-Sn subelments and for increasing the Nb/Cu ratio of these filaments. Increasing the Nb/Cu ratio of the filaments will increase the potential current density of the subelements. A continous Cu wrapping approach will be used to increase the current density of the strand. The wrapping approach also will be used to construct the Cu clad filaments that go into the subelement billet, thereby lowering the fabrication costs of the internal Sn subelements. Phase I demonstrated the contruction of subelement billets with Cu wrapped Nb (and Nb7.5wt%Ta) filaments with both 80/20 and 90/10 Nb/Cu ratios. These subelements were extruded, annealed, and restacked and drawn down to final strands, which were then tested. In addition, an approach for adding Ti to the subelement billet was demonstrated. In Phase II, the billet sizes will be scaled up to full size production billets and restacks. Also, an additional way of introduce Ti into the subelement billet, and incorporating split barriers to lower the AC losses of the strands, will be investigated. Commercial Applications and Other Benefits as described by awardee: The largest market for the technology should be for accelerator and fusion magnets. However, high field magnets (above 5 tesla) can be used for MRI, NMR, high gradient magnetic separators, and superconducting magnetic energy storage applications.