First Field Quality Measurements of a 15 T Nb$_3$Sn Dipole Demonstrator

Within the US Magnet Development Program (MDP) a 15 T Nb3Sn dipole was developed, to demonstrate a magnet design for a post-LHC pp Collider. The magnet design is based on 60 mm aperture 4-layer shell-type coils, graded between the inner and outer layers to maximize the magnet performance. The cable in the two innermost 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. Both cables use RRP Nb3Sn wires produced by Bruker-OST. Magnet coils are surrounded by vertically-split thick iron laminations, con-nected by aluminum I-clamps, and a thick stainless-steel skin. The magnet was tested at the Vertical Magnet Test Facility (VMTF) at Fermilab. This paper reports the first results of magnetic measure-ments of the 15 T Nb3Sn dipole demonstrator including geometrical harmonics, coil magnetization and iron saturation effects. The ex-perimental data are compared with the magnetic calculations.