Stability, Inter-Strand Contact Resistance, and AC Losses in YBCO Roebel Cables

A dc transport current was applied to the strands of a Roebel cable at 77 K in liquid nitrogen bath. The inter-strand contact resistance was measured. It was modified either by applying a pressure on the cable at 77 K in liquid nitrogen bath or using different soldering patterns between the strands of the cable. Magnetization ac losses were measured in frequency range 50-200 Hz in applied magnetic field 4-70 mT perpendicular to the broader face of the cable to test the inter-strand contact resistance effect. High stability and very low level of coupling losses were observed in the cables even with the lowest inter-strand resistances.