The study of Cu fraction influence on Nb/sub 3/Sn strand for ITER performance

In frame of Se.C.R.E.T.S. international task Nb/sub 3/Sn strands with 50 and 60% of Cu fraction have been produced and comparative research of their performance (Q, I/sub c/, J/sub c/, RRR, etc.) have been carried out. Strand design and processing were identical. However, the decrease of Cu fraction value has influenced on RRR value as well as Cr-plated and bare strands. By method of subsequent approximation the estimation of diffusion coefficients of Cr into Cu by R275/R20 values of both strands have been carried out. These calculations have shown that Nb/sub 3/Sn strand after reaction at the standard regime (575/spl deg/C 150 h+650/spl deg/C 200 h at 10/sup -5/ Torr) characterized the value of diffusion coefficient /spl sim/10/sup -12/ cm/sup 2//s, that has led to Cr penetration into oxygen free Cu in not more than 40 /spl mu/m of depth. The calculations of RRR integral value versus reaction time and Cu thickness have also been done. The relation of diffusion coefficient and microstructure of Cu-stabilization has been discussed.