Studies to reduce greenhouse gases emissions from particles detectors operation at the CERN LHC experiments

A wide range of gas mixtures is used to operate different gaseous detectors at the CERN LHC experiments. Some of these gases, namely C$_2$H$_2$F$_4$, CF$_4$, SF$_6$, C$_4$F$_{10}$, are classified as Greenhouse Gases (GHG) with a high Global Warming Potential, therefore subjected to a phase-down policy affecting their price and market availability. These gases are responsible for 70\% of CERN particle detector operation’s direct greenhouse gas emissions. The Organisation’s objective is to reduce such emissions by 28\% by the end of 2024 (baseline year: 2018). The present work shows the development of two main research strategies delineated by the CERN gas group to reduce GHG emissions. Wherever suitable, large detector volumes are operated with recirculating gas systems. The first part of this thesis focuses on optimizing existing gas system technologies to improve operating performances and further reduce gas consumption. In particular, dedicated monitoring infrastructures were designed to properly tune the active control parts of the different gas modules. Furthermore, specific data analysis pipelines were developed to evaluate a gas system’s performance and monitor gas consumption. A second research line examined in this work consisted of studying the performance of RPC detectors operated with eco-friendly gases. RPCs at ATLAS and CMS experiments are operated with a three-component gas mixture mainly based on C$_2$H$_2$F$_4$ (R-134a, GWP$_{100}$ = 1430), around 5\% of \isobutane, and a minor fraction of 0.3\% of SF$_6$ (GWP$_{100}$ = 22800). Due to the presence of leaks at the detector level, C$_2$H$_2$F$_4$ dominates the overall CERN GHG emissions. Alternatives to C$_2$H$_2$F$_4$ were identified in R-1234ze, a molecule in the family of HydroFluoroOlefins with a GWP$_{100}$ = 7, while SF$_6$ alternatives were found in the Novec family (Novec™ 4710 and Novec™ 5110), C$_4$F$_8$O, CF$_3$I, and Amolea™ 1224yd. RPC performance with gas mixtures based on alternative gases was firstly evaluated in laboratory conditions by studying the detector’s efficiency, currents, streamer probability, prompt charge, cluster size, and time resolution. Few selected gas mixtures were then tested at the Gamma Irradiation Facility, which provides muon beam and gamma background radiation, allowing to emulate the High Luminosity LHC background conditions. Few gas mixtures showed similar rate capability performance with respect to the standard gas mixture. Long-term performance studies were started, and preliminary studies on impurities productions for HFO-based gas mixtures are presented, showing the R-1234ze molecule produces an order of magnitude more F$^{-}$ ions than the C$_2$H$_2$F$_4$ one.