Performance analysis of a graded winding pack design for the EU DEMO TF coil in normal and off-normal conditions

The superconducting magnet system plays an important role in the framework of the design of the EU DEMO tokamak. In recent years, ENEA developed a prototype of cable-in-conduit conductor (CICC) with two low-impedance central channels to be used in the DEMO Toroidal Field (TF) coils with a graded winding pack (WP). In this paper, a model of a TF coil based on the thermal-hydraulic code 4C has been developed, including the WP, the steel casing with dedicated cooling channels (CCCs) and the two independent cryogenic circuits cooling the WP and the casing, respectively. The first part of the work analyzes the performance of the WP during a series of standard plasma pulses in normal operating conditions. In the second part different off-normal operating conditions during the plasma pulses are studied, namely the collapse of one or both central channel(s) in the most critical CICCs and the plugging of some CCCs at the most critical locations in the magnet.