AC LOSSES AND CURRENT DISTRIBUTION IN 40 KA NBTI AND NB3SN CONDUCTORS FOR NET/ITER

General working formulas usable for calculations of AC losses in superconducting multi-stage twisted cables have been developed. In situ contact resistances between subcables of different cabling level as well as AC losses have been measured on full size steel jacketed 40 kA NbTi and Nb3Sn conductors developed for NET/ITER applications. In addition to the strand resistive barriers (CuNi inside NbTi strands and chrome plating for Nb3Sn strands) stainless steel spacers have been used inside these cables to reduce the AC losses. Theory and measurements enable to emphasize the role played by the steel spacers in the reduction of the total AC losses of this kind of conductor. The paper gives also conditions for a good compromise between low AC losses (large transverse resistance) and sufficient current transfer (low transverse resistance) that ensures a correct current distribution among strands.