Aging tests of full-scale CMS muon cathode strip chambers

摘要

Two CMS production Cathode Strip Chambers were tested for aging effects in a high-radiation environment at the Gamma Irradiation Facility at CERN. The chambers were irradiated over a large area: in total, about 2.1 m~2 or 700 m of wire in each chamber. The 40% Ar + 50% CO_2 + 10% CF_4 gas mixture was provided by an open-loop gas system for one of the chambers and by a closed-loop re-circulating gas system for the other. After an accumulation of 0.3-0.4 C/cm of a wire, equivalent to about 30-50 years of operation at peak LHC luminosity, no significant changes in gas gain, chamber efficiency and wire signal noise were observed for either of the two chambers. The only consistent signs of aging were a small increase in dark current from ～ 2 to ～ 10 nA per plane of 600 wires and a decrease of strip-to-strip resistance from 1000 to 10-100 GΩ. Disassembly of the chambers revealed deposits on the cathode planes, while the anode wires remained fairly clean.