Results of Ageing Tests on the Forward MSGC 'BANANA' Prototype

The forward tracker of the CMS experiment at CERN will consist of a large number of MicroStrip Gas Chambers ( MSGCs), expected to operate for several years in the high luminosity environment of LHC with an accumulated dose rate of ~ 10 mC/yr per cm of strip. They are planned to be arranged around the interaction point in modular wheels which contain several MSGCs. The 'open'option of a forward CMS 'banana' module includes the electronics inside the gas volume. Long term tests of one such prototype containing two plates, one with gold and the other with chromium strips on diamond-like coated D263 glass with representative electronics and surface mount components inside the gas volume have been performed; the satisfactory results are reported here. A first test has been made with a gas flow rate of 60 cc/min in the prototype ( corresponding to 5 gas renewals per hour) and has shown no gain drop up to 85 mC/cm of accumulated charge per strip. A second test has been performed with a gas flow rate of 6 cc/min corresponding to 1 renewal every two hours, with no gain drop till 73 mC/cm when the experiment was suspended.