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The ac loss characteristics of superconducting wires were obtained and plotted against the field ramp rate of magnet operation. The observations were carried out via an isothermal calorimetric technique on single-strand wires made of niobium titanium, internal-tin and modified jelly-roll (MJR) internal-tin. The results confirmed numerical predictions except for the MJR sample which showed a local maximum during a slow field changing rate.

Further studies on the ramp-rate constraint manifested by the conductors of the US-Demonstration Poloidal Coil (US-DPC) were carried out on a 27-strand cable-in-conduit conductor. The experiment, which simulated the US-DPC test conditions, involved a ramped transport current tuned to a background field with a field ramp rate of 0.5T/s tto 2T/s. Although it did not identify the cause of the ramp-rate limitations, it led to a semi-empirical equation that is valid for both the US-DPC and experimental data.