AC Coupling Losses in CICCs: Analytical Modeling at Different Stages

Cable-in-conduit conductors (CICCs) are composed of a large number of strands (superconducting composites and copper strands) twisted together in several stages with different twist pitches. They are widely used in large fusion tokamaks such as JT-60SA or ITER. However, because of their complex transposed geometry at a strand scale, the knowledge of ac coupling losses in these conductors is limited and still has some improvement margins to capture its complexity while the prediction of their behavior under transient regimes (e.g., central solenoid) is of first importance to assess a safe operation in tokamaks. Consequently, we have carried out an in-depth theoretical generic study of a single stage of a CICC and analytically derived the expression of coupling losses using physical parameters (time constant and partial shielding coefficient) determined from electromagnetic and geometrical properties. Our approach has been inspired by the MPAS model (extensively used on the experimental ITER database) but starts from the analytical description of a single stage and aims at reaching the CICC scale in an iterative way.