Aging studies of CMS muon chamber prototypes

Aging of CMS muon cathode strip chamber prototypes under sustained irradiation was studied. The tests were performed with three prototypes of different gas seal designs and with three gas mixtures Ar(30%)+CO2(50%)+CF4(20%), Ar(30%)+CO2(70%) and Ar(40%)+CO2(50%)+CF4(10%). The CF4-containing mixtures showed no or little aging for an overall accumulated charge per unit of wire length in excess of 13 C/cm. In comparison, the performance deterioration in the Ar–CO2 mixture proved to be very dramatic: the gas gain falls by a factor of 2 for each 0.25 C/cm of accumulated charge.