Discharge mitigation strategies for GE11 detectors in the CMS Experiment

The CMS experiment at the Large Hadron Collider (LHC) has taken successfully data for almost ten years, resulting in the discovery of the Higgs boson in 2012. The LHC will undergo a major upgrade to deliver ten times more pp-collisions in the next two decades, which has been named High Luminosity LHC (HL-LHC). To cope with the increased instantaneous luminosity and increased background levels, the CMS experiment will undergo several upgrades in the next decade. One of these upgrades is installation of Triple-GEM detectors in the forward muon system that will allow better triggering on muons, will increase the muon reconstruction, extend the coverage and increase the number of single measurements. The triple-GEM technology will be installed in three main vacant stations of the muon system: first GE1/1 during the Long Shutdown 2 (LS2) and then, during subsequent shutdowns, GE2/1 and ME0. This technology has been proven to sustain a high-rate environment with performance that fulfil CMS requirements. The Gas Electron Multiplier (GEM) is a new technology for CMS, therefore a test installation of few GE1/1 chambers was performed in 2016 as a proof of concept, commonly referred as the Slice Test. The aim of this thesis arises from the necessity to address a problem emerged during the slice test. During the two years of operation, an increasing read-out channel loss has been observed. This can potentially compromise the muon detection efficiency during HL-LHC and will worsen the overall muon system trigger capabilities. In this thesis I report on the study of the origin of the channel loss and the following R&D program on the possible mitigation strategies. As a result of the study, we proposed and tested a minimal change implementation on the GE1/1 detectors design, that ensures a much stronger endurance of the read-out electronics to discharges, without compromising the schedule for the GE1/1 installation. We also proposed a new design for the GEM foil as a definitive mitigation strategy for the upcoming detectors of GE2/1 and ME0. Finally, the observations on discharges we made throughout the research program, contribute to shed new light on the still not well understood process of discharge propagation in GEM detectors.