Studies on alternative eco-friendly gas mixtures and development of gas recuperation plant for RPC detectors

Abstract

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.