Conceptual Design Study of the High Luminosity LHC Recombination Dipole

The interaction region design of the High-Luminosity LHC requires replacing the recombination dipole magnets (D2) with new ones. The preliminary specifications include an aperture of 10⁵ mm, with 186 mm separation between the twin-aperture axes, and an operating field in the range of 3.5 to 4.5 T. The main design challenge is to decouple the magnetic field in the two apertures and ensure good field quality. In this paper, we present a new approach to address these issues, and provide expected harmonics for geometric, saturation and persistent current effects. The feasibility of an operating field at the high end of the range considered is also discussed, to minimize the D2 magnet length and facilitate the space allocation for other components.