PSI - Issue 24

Andrea Chiappa et al. / Procedia Structural Integrity 24 (2019) 898–905 Andrea Chiappa et al./ Structural Integrity Procedia 00 (2019) 000 – 000

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analysis of deformations (Biancolini et al. (2012)) to upscaling of FEM results (Chiappa et al. (2019)). An extensive review of RBF applications can be found in dedicated textbooks (Biancolini (2018)). In this paper, we expose the results of a mechanical analysis of a TF coil of the DTT facility. We considered the WP as a smeared orthotropic material.

1.1. DTT toroidal field coil system

Di Zenobio et al. (2017) proposed a conceptual design of the DTT superconducting magnet system in 2017. Since then, several updates of the WP geometry and operating parameters occurred. To our knowledge, the latest version of the DTT design, addressed in this paper, is the one reported in the DTT Interim Design Report of April 2019. Eighteen TF coils, featuring superconducting Nb 3 Sn cables (Muzzi et al. (2015)), operate at a peak field of 11.8 T and an operative current of 44 kA. The TF coils work in wedged condition. A full set of Inner Inter-coil Structures (IIS) withstands the shear force acting between adjacent TF coils, and ad-hoc designed Outer Inter-coil Structures (OIS) give support against the out-of-plane loads. The Toroidal Field coils winding pack (WP) is the array of conductor cables, support steel jackets, void filler and wrapping layers enclosed into the SS316LN coil casing for structural reinforcement. Fig. 1 shows the WP structure constituted by 5 Double- Pancakes (DP), 2 “side” Double Pancakes (sDP) and 3 “regular” DPs (rDP) . The 80 superconducting cables feature 0.82 mm Nb3Sn strand (Della Corte et al. (2010), Bessette et a. (2015)), whose superconductivity property enables at extremely low temperatures (4.2 K). A set of superbolts + shear pins has been placed at the ends of the TF straight leg to connect the different D-shaped structures, whereas the in remaining portion of the wedge the coils are simply in contact. The electric current flowing in the cables interact with the magnetic field generated by the moving plasma and the designed devices acting in the DTT facility, producing massive Lorentz forces that are transferred from the conductors to the supporting steel casing by contact.

Fig. 1. Cross section of the TF coil inner leg (left) and rendering (right) of the TF case with details of IIS & OIS.