Resistive Micromegas high-rate and long-term ageing studies at the CERN Gamma Irradiation Facility

.The LHC experiments are undergoing important upgrades for the High Luminosity LHC project. Experiments will be required to operate under three times higher instantaneous luminosity and higher levels of radiation when compared to LHC Run2. The integrated luminosity will increase by a factor ten. To cope with these conditions resistive Micromegas chambers were chosen by the ATLAS experiment as one of the technologies for the upgrade of the first forward muon stations. This paper describes the results of two prototype Micromegas detectors that were installed in the CERN Gamma Irradiation Facility with the aim to evaluate the detector performance under high-rate irradiation and to assess ageing effects over a 2.5 year long irradiation period and an accumulated charge in excess of 0.3 C/cm$^2$.