Development of a gas filter against wire chamber ageing for the MDT chambers in ATLAS

Drift chamber ageing is a serious concern for the operation of the Monitored Drift Tube chambers (MDT) in the ATLAS muon system. Therefore systematic studies of ageing effects have been carried out at the University of Freiburg. It has been shown that tiny contaminations with volatile silicon compounds, which are found in many components supplied by industry, cause a severe degradation of the drift tube performance. Since the ATLAS MDT system contains many thousands of commercial components the cleanliness of all parts cannot be guaranteed. Therefore gas filters with zeolites have been developed in Freiburg, which remove these impurities efficiently. They will be employed in the gas system for the MDT chambers.