Power Loss in ReBCO Racetrack Coils Under AC Applied Magnetic Field and DC Current

Several applications contain windings operating in DC submitted to changing magnetic fields. Their design needs to take the AC loss into account because of cryogenic and energy efficiency issues. This requires either measurements in demonstrators or computer simulations. In this article, we measure and numerically simulate the AC loss in a small racetrack coil made of ReBCO coated conductor. In particular, we study the separate contributions from the magnetization and transport loss. These provide additional information than only the total loss, such as the dynamic magneto-resistance effect. The measurements are done by electrical means and the simulations take a 2D approximation. We found that the total AC loss increases with the DC. However, the magnetization loss presents a peak. Simulations reveal that, contrary to the pure AC situation, the transient state can expand over a few cycles, even when the superconductor presents no flux creep. In conclusion, electrical measurements are useful to determine the AC loss under AC magnetic fields and DC transport current. These can be applied to any operating temperature, in opposition to boil-off methods. Finally, 2D simulation methods can reasonably predict the AC loss in racetrack coils with long straight segments.