We have been developing Nb_3Sn strands by the internal tin diffusion proces.s The strands having low hysteresis loss and high J_c properties and high productivity were developed by optimizing the arrangement of filaments and by using Cu/Ta barrier, respectively. The strand showed 622A/mm~2 as J_c at 12T, 107kJ/m~3 as hysteresis loss for +-3T. In this developmental work, we successfully completed in manufacturing the mass-produced strands of 600km (2.75tons) having excellent properties; 627A/mm~2 as J-c, 134kJ/m~3 as hysteresis loss, 175 as residual resistivity ratio and 3411m as average piece length.
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