Alternative PF Coil Winding Pack Design for the EU DEMO

The EUROfusion DEMO machine is at its pre-conceptual stage. The design of the magnet system for this machine is being developed in collaboration with several European research centers. The Poloidal Field (PF) coils proposed by the Swiss Plasma Center (SPC) use a multiple-in-hand Pancake winding technique. A design based on updated plasma scenarios (2018) was recently proposed. The Winding Pack (WP) aspect ratio was kept close to one, similar to the baseline design in the EUROfusion 2018 DEMO baseline document. In this publication, we study the effects of changing WP aspect ratio. A vertically elongated WP cross-section is beneficial in the reduction of the peak magnetic field at WP cross-section, the machine radial extent, and the hydraulic lengths. However, it increases the bending stress on the WP. An updated PF design is presented. The dimensioning and allocation of materials is based on 3-dimensional electromagnetic calculations. Mechanical performance is evaluated against both dynamic fatigue stress and static stresses. The static stresses are evaluated through 3-dimensional finite element simulations to take into account also the ripple effect of TF coils and increase in bending stresses due to the elongation of the WP cross-section. The thermal-hydraulic analysis verifies a temperature margin of 1.5 K and confirms sufficient coolant flow for the prescribed pressure drop. The quench analysis determines the hot-spot temperatures during various quench scenarios.