AC losses of 19-strand subcables for the ANL 3.3 MJ coil

Designs of multistrand-cable conductors for poloidal field and energy storage coils require low ac losses and cryostability. One way to improve these factors is by compacting or solder filling of the subcables. The 19-strand subcable of the ANL 3.3 MJ coil has been compacted and filled with Sn-50% Pb soft-solder to ensure stable current sharing within the subcable and to improve the mechanical rigidity of the final cable. The purpose of this study is to examine the effects of soldering and cable compacting on the ac losses of the coil and to evaluate the overall cable coupling due to the weakly insulated subcables. From the time constant of the samples and the hysteresis loss measurements of the subcables, it is estimated that approximately 60% of the ac losses of the coil at 6 T/s of the central field are due to the losses within the 19-strand subcable itself. The remaining 40% of the losses seem to come mainly from the coupling among the weakly insulated 19-strand subcables in the final cable. The outer sheath copper wires of the subcable improve the stability of the subcable, especially when it is soldered. It is shown, however, that the ac losses are not increased significantly due to the copper stabilizer