Results from the first operational period of the CF4 recuperation plant for the Cathode Strip Chambers detector at the CERN Compact Muon Solenoid experiment

Cathode Strip Chambers (CSCs) are used in the end-cap 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 polymerization 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 for the CMS CSC is already about 120 kCHF/year, using a closed-loop gas system that is operated at 90 % re-circulation rate. Unfortunately, it is not possible to increase the re-circulation rate 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. The project of a CF₄ recuperation plant was developed and tested on a prototype in the past years. During 2011 the plant was commissioned and it is now running since June 2012. Results from the first operational period are here presented.