The Separation-Recombination Dipole MBRD for the High-Luminosity LHC: From Prototype to Series

The next upgrade for the Large Hadron Collider (LHC), called High-Luminosity LHC, has the aim of increasing the rate of collisions of the accelerator by a factor of ten. To achieve this goal, the dipole and quadrupole magnets before and after the interaction region of the ATLAS and CMS experiments will be replaced. One of these is the separation-recombination dipole MBRD, which features a target integral magnetic field of 35 T $\cdot$ m in a double aperture of 105 mm, obtained with a magnetic field of 4.5 T along a magnetic length of 7.78 m. One of the main challenges in the development of this magnet is the fact that the two apertures must have the same polarity and this causes a magnetic cross-talk between them. Because of this, it has been necessary to develop a left/right asymmetric aperture coil design for the coils to compensate this effect, that would have generated unwanted multipoles. Another problem related to the same polarity in the two apertures is a repulsive Lorentz force between them, which has been managed through the implementation of Al alloy sleeves assembled around the two collared apertures. The design was carried out in the framework of a CERN-INFN Genova agreement and the construction is ongoing in the industry ASG Superconductors. The 1.6 m long model was built and successfully cold tested, followed by the construction of a full-length prototype, recently delivered to CERN, while the construction of the series of 6 magnets is foreseen to be started at the beginning of 2022. This contribution will describe the prototype assembly status, also covering the field quality (FQ) aspect, discussing the results of the warm magnetic measurements at ASG and their implication in the design of the series in terms of harmonic content.