Speaker
Description
During operation, the Cable in Conduit Conductors (CICC) of the ITER Toroidal Field (TF) coils are exposed to severe electromagnetic forces [1]. These forces are in part hoop load and in part crushing load on the strands pressed by the Lorentz-force against the inner wall of the jacket. In addition, the differential thermal contraction between the steel jacket and the superconducting strands during the cooldown generates an additional contribution.
Given this complex stress-strain mechanics, the prediction of the current sharing temperature (Tcs) is not straightforward. However, its calculation during tokamak operation is important to assess accurately the temperature margin.
The concept of effective strain was developed in the past to analyse the performance of the ITER TF samples tested in the SULTAN facility, Villigen, Switzerland [2]. The effective strain was also applied to study the TF Insert (TFI), a single layer solenoid tested in the bore of the CSMC in Naka, Japan [3].
In this work, a methodology based on the cooldown strain and on the crushing strain is assessed from Tcs-measurements performed on straight samples tested in SULTAN during the TFIO campaign under different Lorentz-force conditions [4]. This campaign made it possible to build a large database on the performance of conductors from different manufacturers under different Lorentz-force levels. This allows one to derive the cooldown strain and the dependence of the crushing strain on the Lorentz-force for each type of conductor.
This methodology is then applied to the TF Insert (TFI). The Tcs in the TFI is predicted using the cooldown and crushing strain retrieved from the TFIO tests, and adding the hoop strain computed with FEM models. The predicted Tcs values are then compared with the measured ones. This comparison is important because it confirms that the parameters obtained from tests on straight samples, without the hoop strain contribution, can be applied to a coil.
The same methodology applied to the TF Insert is then applied to predict the Tcs in the TF coils during the tokamak operation. The Tcs maps computed in the TF coils are presented and discussed.
References
[1] C. Sborchia, Y. Fu, R. Gallix, C. Jong, J. Knaster and N. Mitchell, "Design and Specifications of the ITER TF Coils," IEEE Trans. App. Supercond., vol. 18, no. 2, pp. 463-466, 2008,
[2] M. Breschi, D. Bessette, and A.Devred, “Evaluation of effective strain and n-value of ITER TF conductor samples,” IEEE Trans. Appl. Supercond., vol. 21, no. 3, pp. 1969–1973, 2011.
[3] H. Ozeki et al., "Manufacture and Quality Control of Insert Coil With Real ITER TF Conductor," IEEE Trans. App. Supercond., vol. 26, no. 4, pp. 1-4, 2016.
[4] M. Breschi. L Cavallucci, V Tronza, N Mitchell, P Bruzzone and K Sedlak, “Impact of mechanical and thermal cycles at different operating conditions on the ITER toroidal field coil conductor performance,” Supercond. Sci. Technol., vol. 34, Art. no. 085021, 2021.
