Performance of new generation of Resistive Plate Chambers operating with alternative gas mixtures

Abstract

The standard gas mixture for the Resistive Plate Chambers (RPC), composed of C2H2F4/i-C4H10/SF6, allows the detector operation in avalanche mode, as required by the high-luminosity collider experiments. The C2H2F4 and SF6 are now considered to be non-eco-friendly gases for their high Global Warming Potential (GWP). These gases are not recommended for industrial uses anymore, thus their availability will be increasingly difficult over time and the search for an alternative gas mixture is then of absolute priority. There are several studies on going which use different approach to find an alternative gas mixture suitable for experiment which work in high-radiation environment, as those operating at the Large Hadron Collider (LHC). One approach is to replace the standard gas with HFO1234ze/CO2/i-C4H10/SF6, being the HFO1234ze/CO2 the main gas component and obtaining a gas mixture with a GWP ∼ 200. The second approach, currently under study by ATLAS and CMS collaborations, is to introduce a small fraction of CO2 in the standard gas mixture, thus reducing the emissions of C2H2F4. In this presentation the results on the performance achieved using a 1 mm gas gap RPC with both types of gas mixtures are reported. Moreover, the possibility to reduce the SF6 fraction and to replace it at all with a new gas, the HFO1233zd, is also reported. The RPC performance are studied under strong photon irradiation which reproduces the gamma background of the ATLAS cavern and that expected during the High-Luminosity phase of the LHC.