Resistive Micromegas Ageing and Rate Capability Studies at the CERN Gamma Irradiation Facility

Resistive Micromegas, originally developed for the upgrade of the muon system of the ATLAS experiment at LHC, are nowadays used in numerous applications and considered for future experiments as well as upgrades of existing ones. It is then of paramount importance to assess their ageing properties and the behavior under high irradiation. Two resistive Micromegas detectors have been installed in the Gamma Irradiation Facility (GIF++) at CERN in 2015 and continuously operated with a Ar:CO 2 93:7 gas mixture. The detectors have accumulated 0.3 C/cm2, corresponding to a charge equivalent to about 15 years of operations at the highest particle rate expected in Muon systems at High Luminosity LHC runs. The detector current has been constantly monitored over the three years of irradiation. The efficiency for muon detection has been measured before and after the irradiation. Finally, the detector performance, in particular resolution and gain, has been measured as a function of photon background rate with a muon beam combined with a photon background. Based on these results we conclude that the resistive Micromegas under study have a rate capability well beyond 50 kHz/cm2 and did not show any significant performance degradation due to ageing.