Abstract
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.
Highlights
T OKAMAK reactors enable fusion reactions, very hot temperatures must be achieved in the plasma that has to be confined through intense magnetic fields
Each petal is subjected to a Lorentz force of 133.5 N/mm; the analytical models prescribe the application on the flat surface of each petal of 400 N/mm and 177 N/mm, for the rigid model (RM) and the fluid model (FM) respectively
Thanks to the upgrade of the thermal loading simulations with the MULTIFIL code, it is possible to compute the thermal strain for the cool-down simulations, since the strain distributions are not affected by simulation artefacts
Summary
T OKAMAK reactors enable fusion reactions, very hot temperatures must be achieved in the plasma that has to be confined through intense magnetic fields. Since MULTIFIL so far describes only one sub-cable of the CICC (the so called ‘petal’, belonging to the last cabling stage), a novel methodology was developed to account in simulations for the cumulated Lorentz force effect of the other sub-cables on the one under analysis. To this purpose, two different analytical models were used to identify the input boundary conditions for electromagnetic (EM) cycle simulations with MULTIFIL
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