Why do we flush gas in gaseous detectors?

The effects and the origin of the gas degradation in a gaseous detector-based tracker are investigated. The study focused on the so-called T2K gas, which turned out to be highly sensitive to pollutants. In particular the H$_2$O and O$_2$ concentrations were monitored online in different conditions to establish their influence on the gain of the detectors. This pollution was first mitigated by a recirculating and accelerating gas system with the use of a turbine and different absorbers. Further measurements revealed that this pollution originates from a continuous permeation process through the different materials of the gas circuit. In particular, polyurethane-based gas pipes or polyester materials largely increase the level of humidity. As a direct consequence of this work, the gas autonomy of the muon telescopes currently deployed inside the Khufu’s pyramid have been dramatically improved.