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Description
Cathode Strip Chambers (CSCs) are used in the muon system of the CMS experiment (CERN). There are four muon stations on both endcaps consisting of 540 CSCs operating with 40%Ar+50%CO2+10%CF4 gas mixture. The chamber longevity study is particularly important in anticipation of the future LHC upgrade into HL-LHC and the scheduled upgrade of the CMS detector which will result in a significant background increase in the forward region.
The CSC longevity is studied with two CMS CSCs ME1/1 and ME2/1 at the Gamma Irradiation Facility (GIF++, CERN), where the charge accumulation rate is about 30 times higher than that at the HL-LHC conditions. Now the accumulated charge for these CSCs is close to the triple HL-LHC charge value. During the irradiation three working gas mixtures were studied: 40%Ar+CO2 with different fractions of CF4, namely 10%, 5% and 2%. The tests did not show any degradations of the chamber performance.
Search on reduction or possible replacement of the CF4 in the working gas mixture is also ongoing in a laboratory, including the longevity studies with small CSC prototypes.
