Frequency-Dependent Transport AC Losses of Coated Superconductors Up To Tens of Kilohertz

Frequency-dependent transport ac losses of two representative commercial coated superconductors (CCs) at tens of kilohertz band have been experimentally and numerically investigated. It is shown that the ac losses per cycle in metal components of the CCs are not proportional to the applied frequency. Instead, there exists a transition frequency, above which the ac losses decrease continuously. We established a circuit model to understand the underlying mechanism, and found that the current in metal components is not commonly thought eddy current, but a transport current driven by the power supply and surrounding magnetic fields. Meanwhile, we noticed that the geometry of the copper stabilizer plays a significant role on the transport ac losses of CCs, namely, wider copper stabilizers of CCs could bring about much higher losses than theoretical prediction. The underlying reason is the nonuniform current distribution in the copper stabilizers. The obtained results can supplement the existing theoretical description of the ac losses in CCs.