ac losses in cables of twisted multifilament superconductors

The losses due to coupling currents are calculated for a superconducting cable. The cable consists of multifilamentary superconducting wires which are twisted and surrounded by a material of different conductivity. It was found that if the wire twist pitch is different from the cable twist pitch, the losses diverge as1/(1-f), where f is the volume fraction of wire in the cable. The time constant of the cable is increased by a similar factor. These large losses are caused by currents flowing between the wires of the cable and they can be minimized by choosing the correct ratio of cable pitch to wire pitch. (author)