A physical model and numerical method for losses investigation in superconducting cable-in-conduit conductors (CICC) Original Research Article

A reliable prediction of losses in superconducting cable-in-conduit conductors (CICCs) is important for a successful application of fusion and SMES coils, given that every Watt dissipated at 4–5 K requires 400–800 W of electrical power to remove this heat load. There are also losses caused by field transients (like plasma disruption, plasma initiation and step discharge) that may influence the temperature margin in the conductor design. It is commonly supposed that the CICC losses are associated with the so-called coupling losses characterized by the nτ parameter. However, we would like to highlight the importance of the eddy current losses occurring in the external layers of the bundle: in some cases they are greater than the coupling losses. Therefore, the nτ parameter is a simplification and does not accurately describe the real physical processes taking place in a CICC. Also, we believe that the coupling currents (additional currents) generated in loops can either be added to or subtracted from the transport current flowing in superconducting strands, depending on mutual orientation of the varying magnetic flux density and transport current vectors. This can affect the stability margin and the ramp rate limitation of a conductor. The physical model and numerical method for estimating different kinds of losses in CICCs are proposed. The suggested physical model, albeit somewhat incomplete, allows an explanation of some experimental results obtained earlier. The purpose of this work is to develop a method for an independent numerical calculation of the eddy current and coupling current loss components and thereby avoid the costly experiments at the initial stage of the design work.