We studied the systematic effect of current ripple on the determination of n-value, which is the index of the shape of the electric field-current (E-I) curve. Commercial Nb3Sn wires were measured with controlled amounts of ac ripple. Substitution-box, superconductor simulator circuits were also measured. A battery-powered current supply was used to provide the dc with ripple currents. The frequencies of ripple current were 60, 120, and 360 Hz to represent common electrical power harmonics in high-current power supplies. A previous study focused on the effect of ripple on dc critical current (Ic). The current study focuses on how ripple changes the n-value and shows that ripple has a larger effect on n-value than on Ic. We have examined models and measurements on simulators to reproduce and explain the effects observed in measurements on superconductors. We think that current ripple and spikes are sources of differences in n-values measured at different laboratories.
Citation: IEEE Transactions on Applied Superconductivity
Pub Type: Journals
Critical current, current ripple, model calculations, n-value, Nb<sub>3</sub>Sn wire, simulation, superconductor, transport current