Abstract
Individual superconductors are made small to allow flexible manufacturing and low AC losses. When high currents are needed, several conductors are cabled together. These cables can be used to wind magnets or to transmit huge currents in electric power lines with very low losses. In DC use, the superconductor in these cables is lossless, but when the current or external magnetic field varies, AC losses arise in the cables. If a round cable is made of several flat tapes, the aspect ratio of the tape (α = width/thickness) plays an important role in the AC losses. Tapes with high α should be put as close to each other as possible in order to form a superconducting cylinder to reduce the hysteresis losses. However, if α is around 10, it is no longer evident what kind of configuration results in the lowest losses. When α approaches 1, the minimum losses are reached when the tapes do not interact at all. YBCO coated conductors have high α, but Bi-based conductors and MgB2 should not be forgotten. These can offer completely different values of α and thus show different behaviours under AC conditions. In this paper we study how the hysteresis losses of round cables are influenced by the tapes' aspect ratios. We investigate whether it is beneficial to pack the conductors tightly together or to let them operate individually, or whether an intermediate state is preferred. According to the results, there is a break-even α where the tight packing surpasses the individual operation, but the intermediate positioning can result in even lower losses in some cases.