Performance and long-term aging studies on Eco-Friendly Resistive Plate Chamber detectors

TL;DR

The paper tackles replacing high-GWP RPC gases with eco-friendly mixtures based on Tetrafluoropropene and CO₂ and assesses their viability under HL-LHC-like irradiation through long-term aging studies at GIF++. It details the GIF++ experimental setup, including a Cs-137 source, a 100 GeV muon beam, and detectors from multiple experiments, along with HVeff corrections and diverse readout electronics. Baseline tests show >95% efficiency for STD, ECO2, and ECO3, but irradiation and higher CO₂ content increase currents and shift working points, signaling aging effects. The aging campaign indicates that, while efficiencies remain achievable, elevated currents and voltage requirements persist, highlighting both the feasibility and the need for further optimization of eco-friendly RPC gas mixtures for sustained HL-LHC-like operation.

Abstract

Resistive Plate Chambers detectors are extensively used in several domains of Physics. In High Energy Physics, they are typically operated in avalanche mode with a high-performance gas mixture based on Tetrafluoroethane (C2H2F4), a fluorinated high Global Warming Potential greenhouse gas. The RPC EcoGas@GIF++ Collaboration has pursued an intensive R\&D activity to search for new gas mixtures with low environmental impact, fulfilling the performance expected for the LHC operations as well as for future and different applications. Here, results obtained with new eco-friendly gas mixtures based on Tetrafluoropropene and carbon dioxide, even under high-irradiation conditions, will be presented. Long-term aging tests carried out at the CERN Gamma Irradiation Facility will be discussed along with their possible limits and future perspectives.

Figures (10)

• Figure 1: Layout of the GIF++ facility showing $^{137}$Cs source (light brown), the two trolleys with test chambers (dark brown), internal scintillators (blue), external scintillators (black), concrete walls (yellow), and the grey outline. The red arrow indicates the muon beam from the H4 line used for the tests.
• Figure 2: Left: Efficiency and current density, as a function of $\mathrm{HV}_{\mathrm{eff}}$, were measured for the CMS chamber without irradiation, sequentially filled with the STD, ECO2, and ECO3 gas mixtures. Right: same, but for the EP-DT chamber.
• Figure 3: Left: Efficiency and current density versus $HV_{\text{eff}}$ for the LHCb/SHiP chamber operated with the STD mixture, obtained without irradiation, and with ABS = 10 and 2.2. Center: Corresponding results for the same chamber filled with the ECO2 mixture. Right: Same, but with the ECO3 mixture.
• Figure 4: Charge distributions of the signals induced on the 3 cm wide strip of the ATLAS RPC, measured at HVknee , for the STD, ECO2 and ECO3 gas mixtures, from left to right, respectively.
• Figure 5: