Analyses of low- and high-margin Quench Propagation in the European DEMO TF Coil Winding Pack

Superconducting Toroidal Field (TF) coils composed of a winding pack (WP) without radial plates, encapsulated in a steel casing, are currently being studied in the framework of the EUROfusion Work Package Magnets (WPMAG). The ENEA 2014 TF WP design consists of graded (Nb3Sn + NbTi), double-layer wound rectangular cable-in-conduit conductors, for which operational as well as accidental transients must be carefully investigated. The paper presents the analysis of the quench propagation inside the TF WP proposed in 2014 by ENEA using the state-of-the-art thermal-hydraulic code 4C. Different locations are considered for the quench initiation and namely: 1) at the maximum temperature margin DTmarmax, resulting in the most severe hot spot condition and 2) at the minimum temperature margin DTmarmin, to analyze the most probable event. The evolution of voltage, normal zone, hot spot temperature and maximum pressure in the TF WP is computed comparing the results from the two cases, highlighting the role of heat diffusion inside the TF WP.