Calculation method for safe β* in the LHC

∗ CERN, Geneva, Switzerland Abstract One way of increasing the peak luminosity in the LHC is to decrease the beam size at the interaction points by squeezing to smaller values of β ∗ . The LHC is now in a regime where safety and stability determines the limit on β ∗ , as opposed to traditional optics limits. In this paper, we derive a calculation model to determine the safe β ∗ -values based on collimator settings and operational stability of the LHC. This model was used to calculate the settings for the LHC run in 2011. It was found that β ∗ could be decreased from 3.5 m to 1.5 m, which has now successfully been put into operation.