LTS and HTS high current conductor development for DEMO

Highlights: • Design and R&D for DEMO TF conductors. • Wind&react vs. react&wind options for Nb₃Sn high grade TF conductors. • Progress in the manufacture of short length Nb₃Sn proptotypes. • Design and prototype manufacture for high current HTS cabled conductors. - Abstract: The large size of the magnets for DEMO calls for very large operating current in the forced flow conductor. A plain extrapolation from the superconductors in use for ITER is not adequate to fulfill the technical and cost requirements. The proposed DEMO TF magnets is a graded winding using both Nb₃Sn and NbTi conductors, with operating current of 82 kA @ 13.6 T peak field. Two Nb₃Sn prototypes are being built in 2014 reflecting the two approaches suggested by CRPP (react&wind method) and ENEA (wind&react method). The Nb₃Sn strand (overall 200 kg) has been procured at technical specification similar to ITER. Both the Nb₃Sn strand and the high RRR, Cr plated copper wire (400 kg) have been delivered. The cabling trials are carried out at TRATOS Cavi using equipment relevant for long length production. The completion of the manufacture of the two 20 m long prototypes is expected in the end of 2014 and their test is planned in 2015 at CRPP. In the scope of a long term technology development, high current HTS conductors are built at CRPP and ENEA. A DEMO-class prototype conductor is developed and assembled at CRPP: it is a flat cable composed of 20 twisted stacks of coated conductor tape soldered into copper shells. The 10 kA conductor developed at ENEA consists of stacks of coated conductor tape inserted into a slotted and twisted Al core, with a central cooling channel. Samples have been manufactured in industrial environment and the scalability of the process to long production lengths has been proven.