Finite element modelling of cable-in-conduit conductors

The ITER (International Thermonuclear Experimental Reactor) cable-in-conduit conductors (CICCs) are subjected to high thermal and electromagnetic cyclic loadings, responsible for conductivity loss in the strain-sensitive Nb3Sn strands. The complex mechanical phenomena occurring at the local scale of the strands make the final performances of the CICC difficult to predict from single-strand properties. In order to assess the amplitudes of the local strains that drive the conductor electrical behaviour, a nonlinear finite element simulation code is used. The successive stages of the conductors' service life, from the forming of the cable to its thermal cool-down and Lorentz force loading, are simulated. Each strand is individually modelled and contact–friction interactions between the strands are considered. After a description of the issues regarding the modelling of the mechanical behaviour of cables and the main features of the finite element code employed, this paper presents the simulation results for the testing of pure copper wire inclusion for the conductor strain state. The code was then used to model four different cable designs in terms of twist pitches and void fractions. The analysis of the axial strain distributions within the cable is presented here.