AC losses in "in-situ" Nb3Sn-Cu composite conductors

Alternating current loss measurements were performed on "in-situ" Nb3Sn-Cu multifilamentary untwisted ribbon and wire samples. A twisted wire sample was also characterized. The Cu/Nb atomic ratio was 7 and the tin concentration was in the range from 2.4 to 6.9 at. %. The annealing temperature was 550°C for 60 or 288 hours. Critical-current densities were in the range from 5 to 10 × 10⁹A m^-2at 0.2 tesla, 4.2 K. Total losses at 4.2 K have been determined electronically in zero bias field, the frequency range of 20 to 1600 Hz and ac fields up to 0.25 tesla. The results indicate that untwisted samples behave as filamentary conductors with large filaments, one to two orders of magnitude above the real filament size. The effective transverse resistivity of the matrix is very low and eddy current losses correspondingly high.