Aging suppression in Multistrip Multigap Resistive Plate Chambers for high counting rate experiments

Abstract

A long term operation of Multi-Strip Multi-Gap Resistive Plate Chambers (MSMGRPC) with gas mixtures based on C2H2F4 and SF6 leads to aging effects observed as depositions on the surface of the resistive electrodes, especially in the region of the spacers used for defining the gas gaps between the resistive electrodes. The observed higher noise rate and dark current has a negative impact on the performance of the chamber and leads to an increase of the data volume in a free running readout mode operation. MSMGRPC prototypes designed with a direct gas flow through the gas gaps and minimization of the number of spacers in the active area were developed as mitigation solution. Three new prototypes of different granularities were assembled using fishing line as spacers and investigated for aging effects. Although a significant reduction in the dark current and dark counting rate was evidenced, noise rate localized around the fishing line spacers, even though reduced, still remains. In this paper, a new generation of direct flow chambers based on discrete spacers is presented. The results of their aging investigations show that, even at lower gas flows, the aging effects become negligible.