The study of Cu fraction influence on Nb3Sn strand for ITER performance

In frame of Se.C.R.E.T.S. international task Nb,Sn strands with 50 and 60 % of Cu fraction have been produced and comparative research of their perfor mance (Q, I-c, J(c), RRR, etc.) have been carried out. Strand design and pr ocessing were identical. However, the decrease of Cu fraction value has inf luenced on RRR value as well as Cr-plated and bare strands. By method of su bsequent approximation the estimation of diffusion coefficients of Cr into Cu by R275/R20 values of both strands have been carried out. These calculat ions have shown that Nb3Sn strand after reaction at the standard regime (57 5 degrees C 150 h + 650 degrees C 200 h at 10(-5) Torr) characterized the v alue of diffusion coefficient similar to 10(-12) cm(2)/s, that has led to C r penetration into oxygen free Cu in not more than 40 mu m of depth. The ca lculations of RRR integral value versus reaction time and Cu thickness have also been done. The relation of diffusion coefficient and microstructure o f Cu-stabilization has been discussed.