Electromagnetic and mechanical characterisation of ITER CS-MC conductors affected by transverse cyclic loading: I. Coupling current loss

The magnetic field generated by a coil acts on the cable which results in a transverse force on the strands. This affects the interstrand contact resistances (Rc), the coupling current loss and current redistribution during field changes. A special cryogenic press has been built to study the mechanical and electrical properties of full-size ITER conductor samples under transverse, mechanical loading. The cryogenic press can transmit a variable (cyclic) force up to 650 kN/m to a conductor section of 400 mm length at 4.2 K. The jacket is partly opened in order to transmit the force directly onto the cable. In addition a superconducting dipole coil provides the magnetic field required to perform magnetisation measurements using pick-up coils. The various Rc's between strands selected from different positions inside the cable have been studied. The coupling loss time constants (nτ) during and after loading are verified for the Nb3Sn, 45 kA, 10 and 13 T, ITER Model Coil conductors. A summary of the results obtained with up to several tens of full loading cycles is presented. A significant decrease of the cable nτ after several cycles is observed. The values of the nτ's are discussed with respect to the Rc measurements and a multiple time constant model (MTC).