Magnetic Measurements and Analysis of the First 11-T Nb$_3$ Sn 2-in-1 Model for HL-LHC

In the framework of the High-Luminosity upgrade of the Large Hadron Collider, the design and development of new magnets, relying on Nb
₃
Sn superconducting cables, is progressing. In particular, a double-aperture dipole, with a bore diameter of 60 mm and a central field of 11 T, is required for the replacement of some Nb-Ti dipoles in the dispersion suppressor areas. The new magnets must comply with the specifications of the machine in terms of reliability and field quality. An intense short-model campaign was launched in order to validate the design choices. Various single-aperture models have been built and tested. Recently, the first 2-in-1 model has been produced by assembling the collared coils already tested in the single-aperture configuration. This paper presents the analysis of the magnetic measurements on the first 2-m-long, double-aperture demonstrator built and tested at CERN. The geometrical field multipoles, the iron saturation effects, the magnetic cross-talk as well as the effects of persistent currents are presented. The experimental data are compared with the magnetic calculations using the CERN field computation program ROXIE and are discussed in view of the construction of the full-length magnets.