Progress in the design of the superconducting magnets for the EU DEMO

Abstract

In the framework of the DEMOnstration fusion power plant (DEMO) design coordinated by the EUROfusion consortium, a pre-conceptual design of the superconducting magnet system has been developed. For the toroidal field coils (TFCs), three winding pack (WP) options have been proposed; exploring different winding approaches (pancakes vs. layers), and manufacturing techniques (react & wind vs. wind & react Nb 3 Sn). Thermal-hydraulic and mechanical analyses on the three WPs have produced encouraging results, with some critical issues to be solved in future studies and optimizations. The experimental tests on TF prototype short sample conductors have demonstrated a limited performance degradation with electromagnetic cycles and significantly lower effective strains than most of the large-size Nb 3 Sn conductors reported in literature. The toroidal field quench protection circuit has been studied, starting from different topologies and focusing on the most promising one. Two designs are also presented for the central solenoid magnet, with preliminary evaluations on the AC losses during the plasma breakdown. Finally, the design of a TF winding pack based on HTS conductors and the experimental tests on "fusion-relevant" HTS cables are illustrated.

Superconductors for fusion: a roadmap

“…Innovative design and technology solutions are required to meet the challenges of the DEMO magnet system. The strategy concerning magnets adopted pre-CDP until 2020 is presented in [35] and [36]. Demonstration at industrial level and validation of advanced solutions have been included in the CDP work-plan (2021-27).…”

Advance in the conceptual design of the European DEMO magnet system

“…The four TF WP options differ in these design choices. Three out of four design options have already been described in [4], we therefore only briefly mention their key characteristics and update on the latest development. The fourth design, WP#4, is a newly considered one, and it is the only option with radial plates.…”

“…Two variants for the CS coil have been proposed [4] -one based on a Nb3Sn pancake-wound design [28], [29], whereas the other is a hybrid (HTS-Nb3Sn-NbTi) coil based on layer winding [30], [31] and [32]. The latter is more complex from the manufacturing point of view, however provides a more cost-effective design and a slightly higher magnetic flux compared to the Nb3Sn coil of the same outer radius.…”

“…The design activities are organized in the so-called work packages, one of them being dedicated to the magnet system (WPMAG). The progress in the development of the DEMO magnets was reported in the past in [3] and [4]. This paper is dedicated to new achievements in both magnet design and R&D.…”

Validation and results of an approximate model for the stress of a Tokamak toroidal field coil at the inboard midplane

“…This approach is espoused by the EU-DEMO and K-DEMO programs. [12][13][14] This approach likewise increases the structural loads on the TF coil, as the vertical separating force (related to the TF coil tension) scales as F ∝ R 2 . This approach also increases the reactor cost.…”