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Description
The conceptual design of the superconducting magnet system for the DEMO tokamak is being carried out in Europe since a few years. The Toroidal Field (TF) coil requirements and main geometrical features have undergone a series of changes, as a consequence of iterations leading to system-level machine optimization. In particular, solutions with 16 or 18 TF coils have been investigated, operating in the magnetic field range between 12 T and 13 T. At the same time, within the magnet design team different design concepts for the superconducting coils have been investigated, considering Wind & React (W&R) or React & Wind (R&W) manufacturing approaches, as well as layer- or pancake-wound coils. Among various possibilities, ENEA is involved in the design of a layer-wound TF coil, based on rectangular-shaped Cable-in-Conduit conductors and W&R manufacturing approach. In previous years, the feasibility and performance of a large-size Nb3Sn conductor operating at about 82 kA in a 13 T field has been demonstrated. Another key aspect for a layer-wound TF coil has been considered to be the demonstration of a joint between two different conductor grades, and to be possibly manufactured in-line during winding. Beside its feasibility, the performance of a joint between low-field conductor grades, i.e. constituted of a low number of superconducting strands and a high number of stabilization copper wires, had to be verified. Two conductor lengths of the low-field grades have thus been manufactured, characterized by a different number of superconducting wires and different outer dimensions, with an inter-layer joint between them. A sample has been assembled, for a test to be carried out at the SULTAN facility of the Swiss Plasma Center. The present paper summarizes the main features of the conductor design and the manufacturing steps of the two lengths and the connecting joint.
