Performance optimization of internal tin process multifilamentary Nb3Sn strands

•Jc increases by adding Sn cores in the interspaces, hysteresis loss increases at the same time.•Enlarger the number of filaments with the same Sn proportion will increase Jc and hysteresis loss.•Cu split adopted in each sub-element leads to a low hysteresis loss.

In this study, internal tin process Nb3Sn strands for the International Thermo-nuclear Experimental Reactor are developed in Western Superconducting Technologies. Short cable-in-conduit conductors manufactured with these strands have been qualified. Mass production is accomplished, and all the performances of the strands meet the requirement of ITER project. Besides, more researches on the effect of strand design on critical current density and hysteresis loss for Nb3Sn strands are carried out. It is found that critical current density can be enhanced by reducing filament diameter and increasing Sn content, and hysteresis loss of the strands can be significantly reduced through Cu split adopted in sub-element.