Conceptual Magnetic Design of the Large Aperture D2 Dipole for LHC Upgrade

CERN has proposed the High Luminosity upgrade of the Large Hadron Collider (HL-LHC) as an upgrade to the Large Hadron Collider (LHC). As a part of this proposal, the aperture of twin aperture D2 dipole is increased from the present 80 mm to 10⁵ mm without increasing the size of cryostat. This creates a significant challenge in managing saturation induced harmonics and the leakage field, particularly since the field in the two apertures is in the same direction. In addition, small spacing between the two apertures creates significant cross-talk harmonics as well. The expected harmonics based on an initial design were rather large and limited the beam dynamics performance of the machine. This paper will present a series of conceptual magnetic designs which reduce the values of key harmonics by a large amount with expected field errors now comparable to those in most superconducting accelerator magnets.