Speaker
Description
Abstract: Multi-gap Resistive Plate Chamber (MRPC) is a new type of gas detector developed on the base of RPC and it has been applied in many large hadrons experiments to construct time of flight system. Compared with other gas detector, MRPC has relatively narrow gasp gap and its performance is strongly dependent on gas quality. With accelerator luminosity continually growing in recent years, gas quality, related with particle intensity, has become a more and more important factor for gas detector. Such gas pollution effect has been observed on RHIC-STAR muon telescope detector (MTD), where the noise and dark current keep increasing for a very long time after the MTD worked under a relatively higher luminosity physics condition. The time-of-flight (TOF) wall of CBM, proposed to be constructed with MRPC, will work at very high rate (~25kHz/cm2) environment. The gas pollution remains a very important aspect we have to study. We’ve conducted a series of experiments on gas pollution with a 50cm x 50cm 8-gap MRPC. A high intensity X-ray source is used to simulate high particle flux condition and the current recovery time is involved for measuring the extent of gas pollution. The preliminary results show that influence of gas pollution has grown stronger with the increase of the gas box’s volume or the decrease of gas flow rate. To study the volume effect in detail, a self-sealing MRPC with the same 8-gap structure has been developed. The detector works in good condition and 95% of efficiency is obtained in cosmic-ray test. When tested with X-ray irradiation, self-sealing MRPC’s current recovers faster than normal MRPC. This means that the self-sealing structure can improve the gas exchange speed in the chamber. At the same time, a simulation of hydrodynamics based on the SIMPLE-2D method is carried out, intending to confirm the relation between gas pollution and volume. We’ve got the same rule as in the experiment that the maximum concentration of polluted gas grows stronger when MRPC is held in a larger-size flowing volume. All of these shows that the gas pollution is a severe effect at high luminosity experiments, and further study can help us to reduce this effect in the design of CBM-TOF system. (Presentation type: oral)
