Recent Progress in Developing Nb3Sn Conductors With Increased Specific Heat

A possible approach to reducing Nb ₃ Sn magnet training is to increase the energy margin of Nb ₃ Sn conductors by enhancing their specific heat ( C_p ). We have been developing Nb ₃ Sn conductors with increased C_p by incorporating substances with high C_p at 2-10 K based on a conductor design that is compatible with standard Nb ₃ Sn strand production. In the past couple of years our efforts have been mainly focused on improving strand design (e.g., position of high- C_p filaments, thickness of the Cu tube for the high- C_p filaments, ratio of the Cu powder to the high- C_p substance, filament spacing, etc.) in order to obtain good strand drawability and to reduce degradation after rolling, which is needed for production of Rutherford cables. We also tried a new high- C_p substance, Gd ₂ O ₂ S, and verified that it has much higher C_p over the whole magnetic field range than the Gd ₂ O ₃ we used before. With that development work we can now produce high- C_p strands with good drawability and low levels of degradation after rolling. This paper reports our findings and the current status of the development of high- C_p Nb ₃ Sn conductors.