AC losses and current distribution in 40 kA NbTi and Nb/sub 3/Sn conductors for NET/ITER

General working formulas usable for calculations of AC losses in superconducting multistage twisted cables have been developed. In situ contact resistances between subcables of different cabling levels as well as AC losses have been measured on full-size steel jacketed 40-kA NbTi and Nb/sub 3/Sn conductors developed for NET/ITER (International Thermonuclear Engineering Reactor) applications. In addition to the strand resistive barriers, stainless steel spacers have been used inside these cables to reduce the AC losses. Theory and measurements demonstrate the role played by the steel spacers in the reduction of the total AC losses of this kind of conductor. The authors give conditions for a good compromise between low AC losses and sufficient current transfer to ensure a correct current distribution among strands.<>