Theoretical and experimental approach to AC losses in a 40 kA cable for NET

For NET (Next European Torus) application, a 40-kA cable in conduit is being developed. The fabrication technique is expected to be applicable to both NbTi or Nb₃Sn strands. To ensure good overall mechanical behavior of the cable the number of cabling stages has been limited to three and no full insulation has been provided between stages. A theoretical approach to losses has been developed from the basic multifilamentary strand to the last stage, taking into account the complex combined effect of the different twist pitches. Through this evaluation, the contact resistance and the action of stainless steel spacers for the last stage turn out to be sufficient to limit AC losses to an acceptable level in relation to NET specifications. The theoretical approach has been assessed by several experiments: measurements of AC losses on the basic 1.9-mm strand, on triplets, and on six-around-one subcables in relation to compression; measurements of contact resistances in different cases; and evaluation of the action of chrome plating