β*-Reach – IR7 Collimation Hierarchy Limit and Impedance

This report summarises the results of the MD314 about the hierarchy limit of the IR7 collimation system and its impedance. While the activity, the procedures and the results concerning the collimator hierarchy limit are detailed here, the main outcomes from the impedance studies are only briefly reported, as a detailed MD report has been prepared. The MD was carried out during MD block II of 2015, on 29 August, at 6.5 TeV. Different retractions of the IR7 secondary collimators (TCSGs) from the primary collimators (TCPs) were qualified in terms of cleaning inefficiency and impedance. For each retraction, settings of the IR7 movable shower absorbers (TCLAs) tighter than those operationally deployed were qualified as well. Afterwards, the alignment of all IR7 collimators was performed and the beam-based centres compared to those from the alignment done in May 2015, to verify stability. Selected configurations were qualified with loss maps, to spot possible improvements in the cleaning inefficiency due to the alignment. The outcomes are relevant for the potential operation of the LHC at a reduced β∗ in the high luminosity experiments below the nominal value.