Commissioning of the CF4 recuperation plant for the Cathode Strip Chambers detector at the CERN Compact Muon Solenoid experiment

Cathode Strip Chambers (CSC) are used in the endcap region of the Muon spectrometer for the Compact Muon Solenoid (CMS) experiment at the Large Hadron Collider (LHC). The nominal gas mixture contains 40 % Ar, 50 % CO₂ and 10 % CF₄. The main function of CF₄ is to prevent polymerisation processes that would result on deposits on the wires as proved by long-term ageing tests performed during the past few years. CF₄ is an expensive gas; the current gas operational cost in the CMS CSC is about 100 kCHF/year, in a closed-loop gas system that is operated with a 90 % re-circulation rate. Unfortunately, it is not possible to increase the re-circulation fraction because N₂ from air constantly diffuses into the detector. However, the possibility of recuperating the CF₄ would offer several advantages, both in terms of cost and flexibility of operation.