Aging suppression, high time resolution and 2D-position sensitive Multi-Strip Multi-Gap Resistive Plate Counter for high rate experiments

Abstract

The multi-strip, multi-gap resistive plate chambers (MSMGRPCs) of the Time of Flight (TOF) wall of the Compressed Baryonic Matter (CBM) experiment will be exposed to challenging counting rates, up to 50 kHz/cm2. The unprecedented requirement to the CBM-TOF chambers to keep their performance (efficiency over 90% and system time resolution better than 80 ps) at these high counting rates has triggered the development of a new generation of MSMGRPCs with increased counting rate capabilities and suppression of aging effect in high irradiation environment. The MSMGRPCs designed for the low polar angles region of the CBM-TOF wall, besides performing in high counting rate, should also maintain their performance over the lifetime of the experiment. Detailed aging investigation evidenced mainly a gas pollution effect for the chambers with gas exchange via diffusion, enhanced around the spacers. In order to mitigate this phenomenon, a MSMGRPC prototype with a direct gas flow through the gas gaps and a reduced number of spacers in the electric field was developed. Assembling and tests of such prototypes as well as the results of the first aging investigations performed exposing the chamber to a high intensity X-ray flux at different gas flow rates and gas mixtures are reported.