Alternative PF Coil Winding Pack Design for the EU DEMO

Abstract

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 hotspot temperatures during various quench scenarios.

A Combined Electromagnetic and Mechanical Approach for EU-DEMO Toroidal Field Coils

“…The 3D electromagnetic model is made of the three main DEMO magnet systems and also includes an equivalent coil for an ideal plasma wire, as shown in Figure 4a,b. The dimensions and positions used to create the magnet domains are taken from [7,8]. The geometry is built entirely in the APDL environment of Ansys software, with a parametric script to rapidly deal with changes in the structures and to split the domain into different component sub-domains to be able to produce a mapped mesh.…”

“…In DEMO, shown in Figure 1, the toroidal field configuration is obtained with sixteen D-shaped magnets (TF) [5], the vertical field by six poloidal annular coils (PF) [6,7] and the primary transformer circuit by one central solenoid (CS), formed by a stack of five independent modules [8]. Each magnet system in DEMO includes superconductive coils made of Cable-In-Circuit Conductors (CICC) [9].…”

“…For the AISI 316LN (S-N) curve [14], a safety factor of 2 on the equivalent stress amplitude always gives a more conservative limitation, and it has been chosen in our fatigue assessment. The (S-N) relation (best fit of the experimental data) that we employed reads σ alt = 3.90 × 10 27 N 1 8.74 (6) For N = 20,000 cycles, the resulting allowable value is S eq = 462 MPa. As reported in Figures 19 and 20, there are a few localized regions where the S eq reaches the allowable value.…”

Assessment of the Thermal-Hydraulic Performance of the European DEMO NbTi Bus Bars

“…where nτ is the time constant (here taken equal to 0.150 and 0.075 s for the CS [10] and PF bus bars [11], respectively), ANbTi+Cu the total cross section of the strands, 𝐵𝐵 ̇ the time derivative of the magnetic field, μ0 = 4π•10 -7 H•m -1 the magnetic permeability of vacuum, ANbTi the superconductor cross section, df the superconducting filament diameter (here taken equal to 10 μm) and Jc the critical current density, which we evaluate at the maximum value of the magnetic field. We assume that the magnetic field grows following a linear ramp with a duration ΔtB = 10.0 s, and we consider the maximum value of the magnetic field (including background and self-field contributions) Bmax along the whole bus bar length, i.e.…”