LHC Installation Scenarios and Dynamic Aperture

The nominal installation strategy of the LHC assumes that each of the 8 arcs of the ring will be equipped with dipoles coming from the same production line. One of the main arguments used to justify this option was the possibility to compensate most of the non-linearities induced by the dipole field errors via a single corrector circuit per arc and per multipole. Indeed, assuming small variations from magnet to magnet within a given production line, the multipolar components of the main dipoles appear as a systematic per arc in this scenario, which, de facto, guarantees their correctability even with a small number of corrector families. All the tracking studies done so far have used this installation scheme to model the field imperfections of the main LHC magnets. According to latest error tables, with the improvement of the dipole field quality, the uncertainty on the systematic field errors per production line has been strongly reduced and becomes quite comparable or even lower than the random multipolar components expected from dipole to dipole. It is then relevant to check if the present installation scenario is still justified and to compare it with other options less constraining from the installation point of view. Two other options will be studied in terms of dynamic aperture at injection: (1) the case where the dipoles are randomly installed in the LHC tunnel independently of their production line, (2) the case where the dipoles are installed end to end by batches of a small number of magnets (24 dipoles in our study) coming from the same production line. With the error table 9901, the LHC dynamic aperture at injection does not depend significantly on the installation strategy chosen for the main magnets.