Contactless electrical measurements of transport AC losses in a 3 m long superconducting cable

The ac transport losses at 77 K of a 3 m long high-temperature superconducting (HTS) cable conductor were measured electrically using the conventional voltage signals recorded by two pairs of voltage taps (four probe measurements). Further, the signals from two contactless pick-up loops were employed. The contactless loops were placed on the same path as the wiring of the conventional voltage taps outside the cable, whereas the return path went through the centre of the former conductor, thereby encircling all of the superconducting layers. By this arrangement the magnetic part of the ac transport losses of the HTS cable could be singled out. The measurements confirmed that at currents, I, far below the critical current, I_c, of the cable (I ≪ I_c) the losses are dominated by magnetic losses and above I_c the magnetic losses level off and resistive losses become dominating.