Current ripple effect on n-value

We systematically studied the 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 ripple frequencies 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 the determination of dc critical current (I-c); the current study focuses on how ripple changes the n-value and shows that ripple has a larger effect on n-value than on I-c. We examined models and measurements on simulators to reproduce and explain the effects observed in measurements on superconductors. Current ripple and spikes may be sources of differences in n-values measured at different laboratories.