Resistive Plate Chamber (RPC) detectors are widely employed in the muon trigger systems of three experiments at the CERN Large Hadron Collider (LHC). They are operated with gas mixture recirculation systems to reduce operational costs and greenhouse gas emissions since their gas mixture is based on C₂H₂F₄, which has a high global warning potential. It is well known that the C₂H₂F₄ molecule can break down under the effect of radiation and electric field. This leads to the creation of several impurities and free fluoride ions (F^-), which could accumulate under gas recirculation and potentially attach to the RPC bakelite electrode inner surface. For these reasons, an extensive gas analysis campaign has been performed during LHC Run 2 for the CMS RPC system to verify gas mixture quality and possible accumulation of impurities.

During the entire LHC Run 2 period, a gas chromatograph has been used to analyze the RPC gas mixture at different points of the gas system: quality of pure C₂H₂F₄, fresh gas from the mixer, gas at the output of the detectors, and after the purifier module. Several impurities have been found and identified. Few impurities are already present in the C₂H₂F₄ supply, as residuals of the industrial production. Nevertheless, it was found that some of these impurities, as well as others, are created inside the detector gas gap due to the fragmentation of the C₂H₂F₄ molecule under the effects of electric field and radiation.

During the 2018 LHC Run several gas analysis points were added to measure the fluoride ions production in different sectors of the RPC detector system. Indeed the products of the C₂H₂F₄ fragmentation do not always recombine and F^- species can stay free in the gas mixture. F^- analyses were performed on the gas at the output of the detectors both for barrel and endcap regions, where radiation levels and operational conditions were different. In this way, it was possible to correlate the F^- production with integrated charge, and gas mixture flow rate. In parallel, the RPC currents have been constantly monitored to look for possible correlations. Fluoride measurements have also been performed at GIF++ to better understand the correlation between F^- production, radiation levels and gas volume exchanges.

A comprehensive overview of the results obtained from the different types of gas analyses and possible correlation with RPC currents and LHC luminosity will be presented.

电阻板室 (RPC) 探测器广泛用于 CERN 大型强子对撞机 (LHC) 的三个实验的 μ 子触发系统。它们与气体混合物再循环系统一起运行，以降低运营成本和温室气体排放，因为它们的气体混合物基于 C ₂ H ₂ F ₄，具有很高的全球预警潜力。众所周知，C ₂ H ₂ F ₄分子在辐射和电场的作用下会分解。这会导致产生多种杂质和游离氟离子（F ^-)，它可能在气体再循环下积聚，并可能附着在 RPC 电木电极内表面。由于这些原因，在 LHC 运行 2 期间对 CMS RPC 系统进行了广泛的气体分析活动，以验证气体混合物的质量和可能的杂质积累。

在整个 LHC Run 2 期间，气相色谱仪已被用于分析气体系统不同点的 RPC 气体混合物：纯 C ₂ H ₂ F _{4 的质量}、混合器中的新鲜气体、气体输出处的气体。检测器和净化器模块之后。已经发现并鉴定了几种杂质。C ₂ H ₂ F ₄供应中已经存在少量杂质，作为工业生产的残余物。然而，发现这些杂质中的一些以及其他杂质是由于 C ₂ H ₂ F ₄的碎裂而在检测器气隙内产生的。 分子在电场和辐射的作用下。

在 2018 年 LHC 运行期间，增加了几个气体分析点，以测量 RPC 检测器系统不同部分的氟离子产量。事实上，C ₂ H ₂ F ₄碎裂的产物并不总是重新组合并且F ^-物质可以在气体混合物中保持游离。F ^-对筒体和端盖区域的探测器输出处的气体进行分析，其中辐射水平和操作条件不同。通过这种方式，可以将 F ^-具有集成进料和气体混合物流速的生产。同时，不断监测 RPC 电流以寻找可能的相关性。GIF++ 还进行了氟化物测量，以更好地了解 F ^-产生、辐射水平和气体体积交换之间的相关性。

将全面概述从不同类型的气体分析中获得的结果以及与 RPC 电流和 LHC 光度的可能相关性。