Study of the effects of radiation at the CERN Gamma Irradiation Facility on the CMS Drift Tubes muon detector for the HL-LHC

At the High Luminosity Large Hadron Collider the Compact Muon Solenoid detector will need to sustain five times larger instantaneous luminosity and, consequently, much higher levels of radiation, reaching about ten times the LHC integrated luminosity. Irradiation campaigns have been performed to assess the capability of operating under such conditions and to investigate the ageing induced by radiation. One spare CMS Drift Tube chamber installed at the CERN Gamma Irradiation Facility (GIF++) was irradiated with a high activity source along a period of about two years at different source intensities. The measurements of the effects of radiation on the performance of the Drift Tubes expected during the High Luminosity LHC run are presented. Investigations on the outgassing of cell materials and of the gas components used at GIF++ are underway. Strategies to mitigate the ageing effects are also being developed.