A multi-criteria framework for assessing eco-friendly gas alternatives for particle detectors: Case Study of CERN's Resistive Plate Chamber (RPC) Detectors

Greenhouse gas (GHG) emissions from anthropogenic sources are the main contributor to global warming. All sectors, including the particle physics research community, need to optimise their environmental footprint to reach climate neutrality. In particle detection, experiments employ gaseous detectors that operate with mixtures with significant Global Warming Potentials (GWP). Specifically, for the case study, we consider CERN's Resis- tive Plate Chamber (RPC) Detectors operated with a hydrofluorocarbon (HFC) blend - 95.2% R-134a, 4.5% i-C4H10, and 0.3% SF6 yielding a GWP of 3384. Both the R-134a and SF6 components are under the European F-gas regulation and are currently in phase- down, making their supply and cost unpredictable. Previous studies on R-134a alternatives prioritised experimental performance and emissions, yet the studied gases could face more challenges by being included in the upcoming per- and polyfluorinated substances (PFAS) regulation. Here, we present a multi-criteria assessment framework for searching for eco- friendly gas alternatives for particle detectors, focusing on CERN's RPCs, incorporating the detector's performance, gas safety, emissions and market viability. Studies for R-134a and SF6 replacement are ongoing. For R-134a replacement, an ideal substitution is challenging. Nevertheless, adding 30% CO2 to the Standard Gas Mixture can reduce the GWP by almost 15%, ensuring safety, with the gas component remaining commercially accessible and avail- able. Considering the prominence of RPCs in Large Hadron Collider (LHC) experiments, reducing the R-134a consumption will be the direction to reduce GHGs. The developed framework can extend its applicability to other gaseous detectors operating with high-GWP gases beyond high-energy physics.