The Development of MBRD Magnets, the Separation/Recombination Dipoles for the LHC High Luminosity Upgrade

As part of the high-luminosity upgrade of CERN LHC accelerator project, the National Institute of Nuclear Physics (INFN) in Genoa, Italy, has developed the MBRD separation-recombination dipole, also known as D2, whose function is to bring beams into collision before and after the interaction regions of the CMS and ATLAS experiments. It is a NbTi cos-theta double aperture dipole that generates a 4.5 T field in a 105 mm aperture, with a magnetic length of 7.78 m, and has the specific feature that the magnetic field in the two apertures is oriented in the same direction. The agreements between INFN and CERN, signed in 2016 and 2020, called for the construction of a short model, 1.6 m long, a prototype of final size, and the six series magnets, four of which are to be installed in the tunnel and two spare. After an international tender, the construction of all magnets was awarded to ASG Superconductors. The short model was successfully tested at CERN in a vertical cryostat in August 2020, reaching nominal current after three quenches in the second thermal cycle, validating most of the mechanical, thermal, and electrical design and providing important insights into the improvements that were implemented in the prototype. Testing of the D2 cold mass prototype was performed in October 2022. Its performance was found to be extremely good, with no quenches below nominal current even in the first thermal cycle and showing excellent operating margin in terms of current, ramp rate, and temperature. Although the series magnets were designed to be identical to the prototype, some modifications and tuning improvements, including a small cross-sectional refinement, were implemented and assessed with the construction of the first magnet in the series. This contribution reports all the activities that, based on the short model and prototype experience, led us to the construction of the first series magnet.