Recent Progress in Developing Nb3Sn Conductors With Increased Specific Heat

A possible approach to reducing Nb₃Sn magnet training is to increase the energy margin of Nb₃Sn conductors by enhancing their specific heat (C_p). For this study, we have been developing Nb₃Sn 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 Nb₃Sn 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, Gd₂O₂S, and verified that it has much higher C_p over the whole magnetic field range than the Gd₂O₃ 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 Nb₃Sn conductors.