Experimental investigation of a.c. losses in cabled superconductors

Abstract A.c. losses in multifilamentary composite superconducting strands and cables have been measured in adiabatic conditions for transverse field sweep rates up to 50 T s −1 . Measurements were performed on NbTi and Nb 3 Sn conductors of several configurations and surface preparations: single strands, soldered strands and cables of varying degrees of compaction composed of bare strands, strands with CuNi barriers and strands with chrome plating. The experimental data agree well with existing loss models. Loss data are characterized in terms of effective coupling current time constants. It has been determined that chrome plating on strands can reduce the coupling loss in highly compacted cables to as little as 20% of the coupling loss in similar cables composed of bare strands. In loosely compacted cables (down to ≈ 50% void) the strand-to-strand coupling loss was less than the filament coupling loss. As compaction is increased below 50% void the strand coupling quickly increases and becomes the dominant loss mechanism. The data suggest that the total cable loss grows as ≈ 1/(void) 3 below void fractions of 40%. This observed cable loss dependence on void fraction does not agree well with a previously proposed model.