MD2191 – β∗–Reach: 2017 IR7 Collimation Hierarchy Limit and Impedance

This report summarises the results of MD2191 about the hierarchy limit of the LHC collimation system in IR7 at 6.5 TeV and its impedance. The activity was carried out during MD block 3 of 2017, on the night between 17th and 18th September. Measurements were performed mainly on B1, as B2 was dedicated to the follow–up of the impedance measurements of the TCSPM.D4R7.B2 of MD2193 (hence they are not reported here). The hierarchy breakage seen in B1V loss maps in similar activities in 2015 and 2016 when deploying 1 σ–retractions between TCSG and TCP collimators was confirmed. The source, i.e. a possible tank misalignment angle of the TCSG.D4L7.B1 collimator, and its cure, i.e. to compensate the misalignment angle with a suitable tilt of the jaws of the same collimator, was confirmed as well, though not as clearly as it happened in the past; tune shift measurements were mainly devoted to measuring the impact on impedance by applying the compensation angle. The MD activity included a re–alignment of all the IR7 collimators of B1 to the beam. A further verification of the B1V hierarchy breakage and its mitigation was carried out at the end of MD block 4 of 2017, on the night between the 1st and 2nd December, after MD2733. The check is reported here as well for completeness, also because it shows the stability of the origin of the hierarchy breakage and, most importantly, of its solution, confirming the possibility of performing only one angular alignment per year in case of pushing the hierarchy. The MD activity is important for understanding the limitations from impedance and from operational margins; these limitations have direct impact on the choice of the collimation configuration kept during operation, especially in the case of a pushed performance (e.g. when deploying TCSG–TCP retractions in IR7 smaller than those used in operation).