Alternating field losses in superconducting wires carrying dc transport currents. Part 2: multifilamentary composite conductors

Investigations of transient field losses in multifilamentary composite conductors carrying dc transport currents, I, are presented. As shown previously, the total loss is best characterized by a normalized transport current i = l/l_c and a dimensionless field-change rate β = τB_e/B_p, where τ is the relaxation time of the coupling current and B_p is the full-penetration field of a solid conductor equivalent to the multifilamentary composite. For β ? 1, the composite conductor behaves like a solid conductor and a saturation effect occurs in both the magnetization and the ac losses. The characteristic feature of the composite appears for β ? 1, and the total losses for transport currents below i < 1 ? β are almost independent of i. Beyond the limit given, losses rise sharply. Experimental results over a wide range of the field change rate and the transport-current level agree sufficiently with the calculations.