Design, Manufacture, and Test of an 80 kA-Class Nb3Sn Cable-In-Conduit Conductor With Rectangular Geometry and Distributed Pressure Relief Channels

Within the frame of the R&D activities carried out in Europe for the toroidal field coils of the nuclear fusion device DEMO, a fundamental milestone was considered to be the demonstration of Nb₃Sn cable-in-conduit conductors (CICC) performance in the demanding range of interest for DEMO. Among the different technological solutions envisaged, the present paper deals with a wind & react CICC solution, with rectangular geometry, thick steel jacket, and distributed pressure relief channel, designed to operate at 82 kA in a magnetic field of 13 T and with a current sharing temperature T_cs > 6.5 ,K. The main manufacturing steps of the prototype conductor are described in the present paper, carried out within industrial environment, partly using the facilities and procedures available for the manufacture of ITER conductors. A sample was designed for the EDIPO facility at the Swiss Plasma Center, Switzerland, in the configuration usually adopted for the test of ITER poloidal field conductors, where the two straight conductor legs are part of the same cable length, with a continuous transition through a bottom hairpin-type joint, thus avoiding any resistive connection. The conductor has been characterized in terms of dc performance at relevant operating conditions and the absence of any performance degradation with electro-magnetic load cycles has been verified, thus, qualifying the proposed technological solution. AC losses and thermo-hydraulic tests have also been carried out, providing relevant information for further coil design.

I. Introduction

The activities related to the European roadmap for power production by nuclear fusion, coordinated by the EUROFusion Consortium, include the design studies for the DEMO reactor. One of the main R&D aspects was considered to be the feasibility demonstration of the solutions proposed for the DEMO superconducting magnet system [1]. The requirements for DEMO Toroidal Field (TF) conductor are in fact quite challenging in terms of electromagnetic and mechanical performance, to be added to strong cost optimization issues, thus demanding for novel elements and solutions [2], [3]. Different options are being evaluated for the TF coil [4], each presenting new elements with respect to previously developed ones, based on either React&Wind (RW) or Wind&React (WR) Nb₃Sn and on NbTi conductors, with either pancake or layer winding of the coil.