The ATLAS RPC system for the LHC Run-3

Abstract

Resistive Plate Chambers (RPCs) provide the barrel region of the ATLAS detector with an independent muon trigger and a two-coordinate measurement. The chambers, 3720 gas volumes in total covering a surface area of 3650 m2, are arranged in three concentric double layers and operated in a strong magnetic toroidal field.The system was originally designed to operate for 10 years with an instantaneous luminosity up to the LHC nominal value of 1034 cm−2 s−1. After a successful data taking period in Run-2, when the instantaneous luminosity more than doubled its design value, the detector has undergone an intense maintenance to ensure an efficient data taking during the just started Run-3.Several interventions have been carried out on the detector mainly concerning the gas distribution with the aim of stabilizing the system and reducing the amount of gas released into the atmosphere. The main interventions were: (a) new gas distribution racks have been added in order to increase the vertical segmentation and in view of the installation of the new chambers for the phase-2 upgrade, (b) non-return valves have been installed on the chamber outputs to avoid reverse flow with large leaks, (c) a massive repair campaign has been done for fixing the continuously developing leaks, (d) a new repair technique to fix and prevent new leaks has been tested and (e) the segmentation of the HV channels has been doubled in a third of the spectrometer to mitigate the effect of detector failures.The different aspects of the activity carried out in LS2 (Long Shutdown 2) are described, from motivation to implementation. The first measurements to assess the system performance are also presented.