Controlled precompression in Nb3Sn conductors by internal reinforcement with a nonmagnetic steel/molybdenum composite

Searching for an adequate nonmagnetic material for the internal reinforcement of Nb3Sn conductors submitted to large Lorentz forces, the combination Molybdenum + 316 LN steel (austenite stabilized by nitrogen) has been investigated as a model material. It was found that a reinforcement by Mo alone leads to a complete compensation of the precompression on the Nb3Sn filaments exerted by the bronze, thus leading to higher Icvalues. The gradual substitution of Mo by 316 LN steel leads to a decrease of B*c2from 21 T to 16 T, thus reflecting the dominant influence of the reinforcing material (<10 Vol. %) on the precompression. By changing the Mo : steel ratio, the value of ; of the conductor can be set at any design value between 0 and 0.9%. Due to the ductile-to-brittle transition at low temperatures, the application range of Mo is, however, limited. A possible alternative, austenitic Mn steels with low thermal expansion coefficient are proposed.