LSS magnet aperture requirements for the LHC insertion upgrade, a first estimate

A significant reduction of B* will be determinant to push the LHC luminosity by a factor 2 to 10. Beyond the obvious implications this has on the need of designing brand new low-b quadrupole magnets with increased aperture and possibly higher peak field depending on the choice of the technology, this report investigates the various modifications to bring to the matching section magnets Q4 and Q5 and the separation/recombination dipoles D1 and D2. The aim on this report is essentially to activate an R&D effort on the development of moderate gradient (<~ 120 T/m) two-in-one quadrupoles with increased aperture 90 mm diameter) and negligible cross-talk between apertures, but also, based on the ultimate aperture requirements obtained for the D1/Db2 (a gap height of about 120-130 mm for a normal conducting D1 and an inner coil diameter of almost 100 mm for a two-in-one cold D2, assuming a B* of 15 cm), to help in the decision of keeping or not these two magnets warm and cold, respectively.