Both high critical current densities and low hysteresis-losses are needed for Nb3Sn strands used for poloidal coils in a nuclear fusion experimental reactor. It is important for our internaltin route Nb3Sn wires to improve the loss immediately. Recently, we have successfully elucidated the growth mechanism of the bridging, which was the cause of generating the large losses in the internal-tin processed wires. Hence, we tried to improve the loss by means of re-forming the wire construction based on the mechanism. The bridging was completely suppressed by decreasing the diameter of the tin core to 82% and the losses in those wires were decreased to 172-193kJ/m3, which corresponded to 66-59%, comparing with one in a conventional wire. Furthermore, good agreement between estimations from a calculation and actual cross-sectional observations was obtained at the growth position of the bridging, by which we could verify the hypothesis of the growth mechanism of the bridging.
