On a new environment-friendly gas mixture for Resistive Plate Chambers.

The standard gas mixture for the Resistive Plate Chambers (RPC), composed of C 2 H 2 F 4 /i- C 4 H 10 / SF 6 , allows the detector operation in avalanche mode, as required by the high-luminosity collider experiments. The gas density, the low total charge delivered inside the gas and the comfortable avalanche-streamer separation guarantee high detection efficiency, rate capability and slow detector aging. The standard RPC gas mixture is mostly based on Hydrofluorocarbons, HFCs, extensively used in the refrigeration industry. The Hydrofluorocarbons are now considered to be non-eco-friendly gases for their high Global Warming Potential (GWP). The SF 6 has the largest GWP, 22 900, but, due to its low concentration, it contributes only with few tens of units to the total value. The major contribution comes from the main standard gas mixture component, the C 2 H 2 F 4 (GWP ≈ 1300). 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 with low-GWP is then of absolute priority within the RPC community. We report the performance of the RPC working with new environment-friendly gases which could replace the standard mixture. In this work the standard mixture main component, the C 2 H 2 F 4 , is replaced by a proper mixture of CO 2 (GWP = 1) and Tetrafluoropropene ( C 3 H 2 F 4 , GWP ≈ 6). The other high-GWP component, the SF 6 , is replaced by a molecule, the Chloro-Trifluoropropene ( C 3 H 2 ClF 3 , GWP ≈ 5) never tested in RPC detectors. The mixtures studied have a total GWP ≈ 10. We report, for several eco-gas mixtures, the detection efficiency, streamer probability, electronic and ionic charge as a function of the high voltage. Moreover, the timing properties are studied and the detector time resolution is measured. We also focus the attention on a new category of signals having intermediate properties between avalanche and streamer, called "transition events". This category is negligible for the standard gas mixture but relevant for HFO/ CO 2 -based gas mixtures. We show a direct comparison between SF 6 and C 3 H 2 ClF 3 to study in depth the possibility to replace the SF 6. [ABSTRACT FROM AUTHOR]