AC-losses in the ECN concept of the NET-TF-conductor

Analysis of the conditions on the toroidal-field coils of the Next European Torus machine indicates that the largest AC-loss contributions are to be expected from coupling losses in the flat superconducting cable, and to a lesser extent from hysteresis losses in the niobium-tin filaments. Coupling losses are caused by currents in a transverse direction induced by the pulsed field perpendicular to the broad side of the cable. These losses are inversely proportional to the transverse resistivity of the cable. The influence on the transverse resistivity of wires having a copper-nickel shell around the wire-filament zone was verified experimentally. Theoretical calculations of the transverse resistivity of the flat cable are discussed. Hysteresis losses in a perpendicular AC field were measured experimentally in two types of multifilamentary niobium-tin wire, both having hollow filaments. A simple model for calculating hysteresis losses in hollow filaments is also reported.