Alternating field losses in mixed matrix multifilament superconductors

Losses were calculated for and measured at 4.2°K in two mixed-matrix superconductors for the cases of transverse applied alternating fields superimposed upon zero or 5T transverse bias fields. The 0.080 in. × 0.160 in. conductors are composites of copper-sheathed Nb-Ti filaments twisted every 5 cm within a copper-nickel matrix, where the copper-nickel to copper to superconductor ratio is nominally 4:4:1. The conductors differ only in the copper-nickel alloy of the matrix and the associated matrix conductivities, sigmamcalorimetric measurements were performed with alternating fields ranging in frequency, f, from 0.3 to 12,800 Hz and from 2500 to 4 oersteds in amplitude Hm. Eddy current losses consistent with the theory and proportional toHₘ²f²σₘandHₘ²f/σₘwere observed. The measured losses were found to be less than the calculated losses and within 45% of the calculated losses in all cases.