AC Loss Modeling of a CORC Cable via an Analytical Equation and Finite Elements

High temperature superconducting (HTS) fusion magnets must avoid quenching when subjected to a rapidly changing field, in normal operation and due to transient events. To this end, correct understanding of the AC losses is key. Their calculation in structures made with HTS tapes such as conductor on round core (CORC), twisted stacked tape conductor (TSTC), etc., still faces challenges due to the unique structure and geometry of the HTS tapes – normally made of Rare-Earth Barium Copper Oxide (REBCO) – in addition to twisting and/or transposition. To estimate the losses in the CORC cable of a poloidal field magnet carrying being subjected to a sinusoidal waveform field and/or current, two methods are used in this article. First, the well-established H-formulation via the finite element method. Second, an analytical formula, available in literature, for calculating the hysteresis loss in a straight tape. It is then shown that the typically 3D finite element model (FEM) problem of AC loss in twisted and transposed tapes in CORCs can be simulated in 2D when the peak background field is high. Simultaneously, the analytical formula is corrected for a twisted and transposed tape, allowing to analytically model twisted and transposed tape assemblies such as CORC. A comparison is made between the results of the two AC loss calculation methods, demonstrating the limitations of the analytical calculation, but also that a close match in the loss is possible under certain conditions.