Long-term study of optimal gas purifiers for the RPC systems at LHC

This study investigates the impurities produced in the gas of heavily irradiated RPC chambers and the properties of possible purifiers for the closed-loop gas systems used in the LHC experiments. The goal is finding the operational conditions that will keep the RPC gas purity near the level of the fresh gas quality to ensure proper operation of the large RPC systems at high luminosity. The properties and performance of a large number of purifiers have been understood. On that basis, an optimal combination of different filters consisting of MS (MS) 5Å and 4Å, and a CuO catalyst R11 has been chosen and validated irradiating a set of RPCs at the CERN Gamma Irradiation Facility (GIF) for several years. An important feature of this new filters configuration is the increase of the cycle duration for each purifier, which results in better stability and reduced downtime of the gas systems. If needed, it permits to comfortably increase the gas flow in the detectors during the high luminosity running at LHC.