Resistive Plate Chambers (RPCs) are widely used in particle physics applications, including the CERN LHC experiments. RPCs are often operated with a gas mixture containing C2H2F4 and SF6, both greenhouse gases (GHGs) with a high global warming potential (GWP). The reduction of GHG emissions and the search for eco-friendly alternatives are crucial for use of RPCs in future since F-gases are being phased out in Europe.
The best way to immediately reduce GHG emissions is to use gas recirculation systems. In parallel, CERN gas team is developing a new recuperation system specifically conceived for C2H2F4 and SF6, where good performance has been achieved.
For long-term operation, low GWP gases are studied. Hydrofluoroolefins (HFO), chlorofluorocarbons and 3M Novec are identified as possible replacements for C2H2F4 and SF6. Several eco-friendly gas mixtures were investigated on 2 mm gap RPCs, by measuring detector performance, i.e. efficiency, streamer probability, induced charge, cluster size and time resolution. Studies were done in laboratory and at the CERN Gamma Irradiation Facility (GIF++), which provides a muon beam combined with a gamma source. Comparative analyses were performed between RPC operated with standard mixture and mixtures containing HFO with the addition of He or CO2 or mixtures with alternatives to SF6.
Long-term studies have started at GIF++ where RPCs are operated under recirculation with eco-friendly mixtures to evaluate possible long-term aging effects.