The CMS Muon System and Features of Its Operation with HL-LHC

The muon system of the CMS facility (CERN) is presented. It uses detectors of three types: drift tubes, resistive plate chambers, and cathode-strip chambers. The characteristics of the muon system in the period of the CMS data taking in pp collisions during 2016–2018 are presented. Plans for the development of the muon system in the Phase II upgrade of the CMS project are presented. The problems of replacing greenhouse gases used in CMS muon detectors with gases with a lower global warming potential are discussed. The results of studying the effects of radiation aging of cathode-strip chambers at the GIF++ facility (CERN) are presented. The possibility of CSC operation with a reduced content of CF₄ in the working gas mixture is being investigated.