Development and First Test of the 15 T Nb$_3$Sn Dipole Demonstrator MDPCT1

Fermilab in the framework of the U.S. Magnet Devel-opment Program (MDP) has developed a Nb$_3$Sn dipole demonstrator for a post-LHC hadron collider. The magnet uses 60-mm aperture 4-layer shell-type graded coils. The cable in the two inner-most layers has 28 strands 1.0 mm in diameter and the cable in the two outermost layers has 40 strands 0.7 mm in diameter. An inno-vative mechanical structure based on aluminum I-clamps and a thick stainless steel skin is used to preload Nb$_3$Sn coils and support large Lorentz forces. The maximum field for this magnet is limited by 15 T due to mechanical considerations. The first magnet assembly was done with lower coil pre-load to achieve 14 T and minimize the risk of coil damage during assembly. This paper describes the magnet design and the details of its assembly procedure, and re-ports the results of its cold tests.