Advanced modeling of electromagnetic loading of cable-in-conduit conductors for fusion magnets

The electrical performance degradation of Nb3Sn cables in the Cable-in-Conduit Conductors CICC has been well documented in literature. The Nb3Sn composite strands exhibit a critical current density that strongly depends on the strain state of the superconducting filaments. During a fusion magnet operation, the conductors are submitted to several electromagnetic and thermal cycles affecting the Nb3Sn mechanical state and consequently the capacity of the conductors to transport current. Different studies based on both a macroscopic and microscopic approaches have been performed so far to identify the mechanisms determining the conductors’ behavior. Nevertheless, no theory permitting to predict the electrical performance of cyclically loaded conductors has been developed yet. Therefore, a solid electromechanical model able to tackle the analysis of CICC for fusion cables when they undergo thousands of cyclic loadings would be very useful. In this paper an advanced mechanical model to study the mechanical behavior of ITER TF CICC based on an improved version of the MULTIFIL finite element code is presented. A correction is introduced to solve the problem of the large impact of the boundary conditions in the simulation of the thermal loading, encountered in a previous work. A novel methodology to identify the value of thermal strain to be applied in cool-down simulations has also been developed. The model was adapted to take into account the Lorentz force cumulative effect of the other petals on the one under analysis. An assessment of the electromagnetic behavior based on the mechanical analysis is also presented.