Evolution of Contact Resistance and Coupling Loss in Prototype ITER PF NbTi Conductors Under Transverse Cyclic Load

Cyclic energizing of a magnet coil with Cable in Conduit Conductors (CICC), as for fusion applications, results in an anomalous change of the interstrand contact resistance ( ) and coupling loss ( ) due to the alternating transverse forces. Previously, three Nb3Sn ITER conductors have been tested in a cryogenic press, up to 40 cycles. Now, for the first time, the behavior of NbTi conductors under cyclic load is investigated and results are presented for three full-size prototype ITER Poloidal Field (PF) Coil conductors. One conductor has bare copper strands and no petal wrapping while the others have a Cr and solder strand surface coating. The press can transmit a maximum transverse force of 800 kN/m directly to a cable section of 400 mm length at 4.2 K. Each conductor is tested up to 220 kN/m and 40,000 full loading cycles. The magnetization of the conductors and the between combinations of strands and strand bundles is measured at various number of cycles. It appears that the can vary for up to orders of magnitude during cyclic loading.