Magnetic Measurements and Analysis of the First 11-T Nb3Sn Dipole Models Developed at CERN for HL-LHC

The high-luminosity upgrade for the LHC (HL-LHC) envisages the replacement of some 15-m-long NbTi dipoles in the dispersion suppressor area by shorter Nb
₃
Sn magnets with a nominal field of 11 T. The new magnets must be compatible with the lattice and other main systems of the LHC. The shorter length of new units will allow the installation of collimators. The successful use of the Nb
₃
Sn technology requires an intense R&D program, and therefore, a CERN-Fermilab joint development program was established. This paper describes the magnetic measurement procedure and presents the analysis of the magnetic measurements on the first 2-m-long single-aperture demonstrators built and tested at CERN. The geometrical field multipoles, the iron saturation effects, and 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 requirements for machine operation.