Magnetic Studies of AC Loss in Pressurized Rutherford Cables with Coated Strands and Resistive Cores

Abstract

The most recent results in an ongoing study of the influence of interstrand crossover contact resistance, R_c, strand coating, and cable design, on coupling (eddy current) loss in NbTi-strand Rutherford cables for advanced accelerator applications are presented and discussed. Inductive measurements of AC loss in six-layer stacks of Rutherford cable have been made with the applied field both normal to and parallel to the plane of the cable. Cables studied had bare-Cu, Ni-plated, and stabrite-coated strands; the latter were also furnished with metallic or insulating interlayers (cores) of, respectively, unalloyed Ti, stainless steel, and kapton ribbon. The cable packs were cured under pressure (-90 MPa) at temperatures of 150 to 250°C. After pressure release the AC loss was measured under pressures of 0, 36, and 78 MPa. Lowest coupling loss was obtained with bare Cu cable provided the curing temperature was kept below 200°C. The stabrite cable, which exhibited relatively low loss when cured below 170°C and measured under zero pressure, became extremely lossy under 36 MPa and even more so under 78 MPa. Insertion of any of the ribbon interlayers into the stabrite cable tended to eliminate the R_c-based coupling loss, resulting in a cable whose AC loss was small, controllable, and independent of final pressure.