Sorting Strategies for the LHC Dipoles

Sorting strategies are investigated in view of improving the dynamic aperture of the CERN-LHC. Dynamical quantities, computed with perturbative tools of non-linear maps (normal forms), are used as quality factors. They provide a fast estimate of beam stability well-correlated with the results of element-by-element tracking simulations. The most effective quality factor is retained and maximised by an appropriate permutation of the position of the dipoles along the LHC azimuth. The search is made faster by magnet pairing based on local compensation of the random field-shape imperfections. The robustness of the proposed solution is finally checked through extensive tracking of realistic models of the LHC lattice.