AC Loss Characteristics in REBCO Coil Assemblies With Different Geometries and Conductors

We have been seeking effective ways to reduce ac losses in REBCO coil assemblies. The ac loss characteristics of assemblies of REBCO double-pancake coils (DPCs) are influenced by the magnetic interactions between coils as well as the electric field (E)-current density (J) characteristics of REBCO coated conductors. We compared the ac loss characteristics of two assemblies of DPCs obtained by electromagnetic field analysis and experiment: one consisting of two DPCs and another consisting of six DPCs. Prior to the electromagnetic field analyses, we measured the current transport properties of the coated conductors and formulated their E-J characteristics. In the assembly of six DPCs, ac loss concentrates in the end PCs. In order to reduce the ac loss there, we replaced the end DPCs with ones wound with coated conductors with higher critical currents. However, the conductor replacing is not effective so much to reduce the ac loss because of magnetic interactions between DPCs.