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REBCO coated conductors are exposed to rotating magnetic fields in various high-temperature superconducting (HTS) applications, such as HTS rotating machines and flux pumps. AC loss will be generated in the conductors when they carry AC current under rotating magnetic fields. We define AC loss in the coated conductors with and without current as total AC loss and magnetization loss, respectively. In this work, total AC loss and magnetization loss, in a REBCO tape under rotating magnetic fields and a perpendicular AC standing wave magnetic field are numerically investigated. We employ a 2D finite element method (FEM) based on the ${T} - {A}$ formulation, where ${T}$ and ${A}$ , are the current and magnetic vector potentials, respectively. In the simulations, the external magnetic field amplitude ( $B_{\mathrm {m}}$ ) is up to 500 mT and the reduced AC current ( $i$ = $I_{\mathrm {t}}/I_{\mathrm {c0}}$ ) varies from 0.1 to 0.9, where the $I_{\mathrm {t}}$ and $I_{\mathrm {c0}}$ are the amplitude of the transport current and self-field critical current of the conductor, respectively. Two different types of rotating fields are considered: one is a uniform field with equal amplitudes and phases at each position, and the other being a non-uniform field created by a rotating Halbach array. Different tape widths ranging from 4 mm to 40 mm are considered. Interestingly, the simulation results show substantially higher magnetization loss in the perpendicular standing wave compared to the rotating magnetic fields when $B_{\mathrm {m}}$ is over 100 mT. We attribute the result to the fact that the magnetization loss is propotional to $J_{\mathrm {c}}$ of the conductor at magnetic field amplitudes much greater than the effective penetration magnetic field. Evidently, the instantaneous loss curves of the SW model and RMF-Uniform model at 200 mT exhibited close similarity with evolving $J_{\mathrm {c}}$ values of the two models. Furthermore, when $B_{\mathrm {m}}$ is lower than the effective penetrated field, we observe a pronounced disparity in magnetization loss of the wider tape between uniform and non-uniform rotating fields. This highlights the importance of considering the effects of non-uniform field distribution, particularly at lower magnetic field. We further show that total AC loss under the perpendicular standing wave magnetic field remains greater than that under rotating magnetic fields when $B_{\mathrm {m}} > $ 100 mT and $i < 0.5$ .

When a magnet wound with coated conductors generates a time-dependent magnetic field, ac losses are generated in coils of the magnet. We have developed a three-dimensional model for electromagnetic field analyses of multilayered coils composing a cosine-theta dipole magnet with an iron yoke. The influence of the iron yoke is considered as the image currents in the iron yoke. Using this model, we conducted electromagnetic field analyses of a dipole magnet, which was designed from the specifications of a rotating gantry for carbon cancer therapy. The time-dependent spatial distributions of ac losses were obtained from the results of electromagnetic field analyses when the magnet was excited at 20 and 30 K. The feasibility of conduction-cooled magnets for the rotating gantry is discussed from the viewpoint of the heat load by ac losses. [ABSTRACT FROM AUTHOR]

We have been seeking effective ways to reduce ac losses in REBCO coil assemblies. The ac loss characteristics of assemblies ofREBCOdouble-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. [ABSTRACT FROM AUTHOR]

We carried out electromagnetic field analyses on the shielding-current-induced field (SCIF) of a cosine-theta dipole magnet, which is wound with coated conductors with finite electric field (E)-current density (J) characteristics and must ramp up its magnetic field. E-J characteristics, which depend on the field amplitude and orientation, were formulated based on the measured E-J data and were used for the analyses. The distributions of E in coated conductors of the magnet during the ramp-up phase as well as the flat top of the magnet excitation was revealed, and the relevant range of E-J characteristics of coated conductors was discussed from the viewpoint of dominating shielding currents. The influences of the variation of the E-J characteristic and the field ramp-up rate on SCIF were examined. [ABSTRACT FROM AUTHOR]

Because the coefficient matrix is dense in the electromagnetic-field-analysis models of coated conductors using current vector potentials, the analyses of large-scale coils require a large amount of memory and long computation time. In this paper, we introduce hierarchical matrices by using the HACApK library in order to reduce both memory consumption and computation time. The effect of the method with respect to memory consumption and computation time is examined in numerical tests using a pancake coil wound with a coated conductor. The effect of parallel computations is also examined. Finally, we analyzed a large-scale magnet, with 1.5 million unknown values. [ABSTRACT FROM AUTHOR]