Controlled precompression in Nb<inf>3</inf>Sn conductors by internal reinforcement with a nonmagnetic steel/molybdenum composite

Abstract

Searching for an adequate nonmagnetic material for the internal reinforcement of Nb <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</inf> Sn 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 Nb <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</inf> Sn filaments exerted by the bronze, thus leading to higher I <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">c</inf> values. The gradual substitution of Mo by 316 LN steel leads to a decrease of B* <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">c2</inf> from 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 <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">\varepsilon_{m}</tex> ; 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.