Gas related effects on multi-gap RPC performance in high luminosity experiments

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The Multi-gap Resistive Plate Chamber (MRPC) is a new type of gas detector developed in recent years. It has excellent time resolution (better than 100 ps) and high efficiency (higher than 95%). This detector has been used to construct large-area time-of-flight (TOF) system in many nuclear and particle physics experiments. However, as a type of gaseous detector, the aging of the gas mixture under long-time exposure to ionizing radiation cannot be neglected. With the increase of accelerator luminosity, impurities in the gas mixture can be potentially dangerous for long-term operation of the MRPC. This has been observed in some experiments, for example with the RHIC-STAR muon telescope detector. The CBM-TOF, used for hadron identification, is proposed to be assembled with MRPCs. These counters have to stand particle fluxes as high as 25 kHz/cm2, and thus the gas pollution is a critical aspect to be studied. In order to better understand the gas quality's impact on the MRPC performance, a two-dimensional simulation based on the SIMPLE algorithm is carried out to imitate the distribution of impurities in a MRPC gas box. The preliminary results show that gas pollution grows stronger with the increase of the gas-flowing volume. In addition, we conducted a series of experiments with a 50 × 50 cm2, 8-gap MRPC prototype. The results match the simulation quite well. Gas pollution indeed has a severe impact on the MRPC performance, and further study can be very useful to reduce gas aging effects in high-luminosity experiments.