Study of the ecological gas for MRPCs

Abstract

The Multigap Resistive Plate Chamber (MRPC) is a gaseous detector; the performance depends very much on the gas mixture as well as the design. MRPCs are used as a timing device in several collider experiments and cosmic ray experiments thanks to the excellent timing performance. The typical gas mixtures of RPC-type detectors at current experiments are based on the gases ${\mathrm{C}}_2{\mathrm{F}}_4{\mathrm{H}}_2$ and $\mathrm{S}{\mathrm{F}}_6$. These gases have very high Global Warming Potential (GWP) values of 1430 and 23900 respectively. The present contribution has been performed as a part of efforts to reduce the amount of greenhouse gases used in high energy experiments. The performance of MRPC has been measured with two different gas mixtures; ${\mathrm{C}}_2{\mathrm{F}}_4{\mathrm{H}}_2$ based gas mixtures and the ecological ${\mathrm{C}}_3{\mathrm{F}}_4{\mathrm{H}}_2$ (HFO-1234ze). A small MRPC was used for the tests. It has an sensitive area of 20 $\times$ 20 $\mathrm{c}{\mathrm{m}}^2$; it was been built with 6 gaps of 220 $\mu$m. In normal operation, the strong space charge created within the gas avalanche limits the avalanche's growth. $\mathrm{S}{\mathrm{F}}_6$ plays an important part in the process due to its high attachment coefficient at low electric fields. It is thus necessary to find another gas that has a similar attachment coefficient. $\mathrm{C}{\mathrm{F}}_3\mathrm{I}$ is a possible candidate. Tests were performed with this gas added to ${\mathrm{C}}_3{\mathrm{F}}_4{\mathrm{H}}_2$.