Design and Qualification of LTS Conductors at CEA for EU-DEMO Toroidal Field Magnet

The EU-DEMO baseline follows the path towards a large-scale tokamak demonstrator. The unmatched size stands as one of the biggest challenge to overcome. Toroidal field magnets are no exception and the expanding performance and limits require the development of new conductor designs. In this regard, CEA design team has been working on the scaling-up of ITER-like conductor technology, with the design, manufacture and test of a square-in-square 100 kA-class conductor called DEMOTF-WP3. It has now been tested in SULTAN and this article presents preliminary results. The sample is composed by two legs containing the same 3.5 m long CICC for redundancy purpose. Voltage taps and temperature sensors are installed along both legs following a symmetrical scheme. This sample also contains a twinbox joint prototype connecting the two legs together at the bottom of the sample thanks to a thin layer of compacted indium. Furthermore, the need expressed at EU-DEMO Gate 1 review to investigate round-in-round geometry permitting the use of radial plates, triggered the CEA design team to propose another Nb₃Sn conductor design (DEMOTF-WP4), with operating current of 116 kA and peak field of 12.5 T. This conductor is composed of 721 SC strands and 1108 copper strands cabled together within a round stainless steel jacket with a diameter of 55 mm. The detailed design is presented along with the prototype manufactured that will be used for the qualification tests to be held at SULTAN facility at CRPP in 2025.