Resistive plate chamber operation with new environmentally friendly gases

Resistive Plate Chamber (RPC) detectors are widely employed in the muon trigger systems of three experiments at the Large Hadron Collider (LHC) thanks to an excellent time resolution. A gas mixture composed of C₂H₂F₄, iC₄H₁₀ and SF₆ is used for LHC RPCs operation in avalanche mode. C₂H₂F₄ and SF₆ have a Global Warming Potential (GWP) of 1430 and 23900 respectively, classifying them as greenhouse gases. The search of new environmentally friendly gas mixtures is advisable for reducing greenhouse gas emissions, operational costs as well as to optimize RPC performance and possible detector aging issues. Two eco-friendly candidates have been identified for substitution of C₂H₂F₄: R1234yf and R1234ze with a GWP of 4 and 6, respectively. A dedicated experimental set-up has been implemented to study single-gap RPC performance in terms of avalanche and streamer operation together with the evaluation of the quenching and electronegative capacities of the selected environmentally friendly Freon. Several new gas mixtures making use of only very low GWP gases have been tested. The first tests confirm that the simple replacement of C₂H₂F₄ and SF₆ with the new Freon is not possible and the addition of more reactive gases is necessary to achieve the required performance at LHC. RPCs have been successfully operated in streamer mode in a mixture of R1234yf, Ar and iC₄H₁₀.