Design validation of the CMS Phase-2 Triple-GEM detectors

The High-Luminosity LHC will deliver proton-proton collisions at 5.0-7.5 times the nominal LHC luminosity, with an expected number of 140-200 pp-interactions per bunch crossing. To maintain the performance of muon triggering and reconstruction under high background, the forward part of the Muon spectrometer of the CMS experiment will be upgraded with Gas Electron Multipliers (GEM) and improved Resistive Plate Chambers detectors. Particularly challenging is the extension of the pseudorapidity of the muon system up to |η| < 2.8 with a 6-layer station, named ME0, that will be installed behind the new high granularity calorimeter and that will see particle rates up to 150 kHz/cm2 and integrate a dose of 250 krad by the end of the High Luminosity phase of the LHC. In this contribution we will present the major design changes of the Triple-GEM detectors to adapt them for the harsh radiation environment and the high particle rate. We shall summarize the performance of prototype Triple-GEM detectors measured with X-rays and gamma at the CERN GIF++ irradiation facility.