The CMS micro-strip gas chamber project - development of a high-resolutiontracking detector for harsh radiation environments

Thirty-two large-area Micro-Strip Gas Chambers were tested in a high-intens ity, 350 MeV pion beam at PSI to prove that we had reached a Milestone for the Compact Muon Solenoid (CMS) experiment. The particle rate was approxima tely 6 kHz/mm(2), distributed over the whole active area of the detectors. and this rate was maintained for a total integrated time of 493 h. All of t he chambers were operated with signal-to-noise values at or above that corr esponding to 98% hit detection efficiency at CMS; the average SIN was 31. N o indications of any gain instabilities or ageing effects were observed. In the official 3-week Milestone period, three strips from a total of 16 384 were damaged, a result which is 20 times lower than the minimal requirement for CMS. The spark rate of the detectors was very low and decreased with t ime to an average of one spark per chamber per day. The cathode voltages of 24 of the chambers were increased over a one week period to investigate th e behaviour of the detectors at higher gains: the maximum S/N value was 2.4 times that at the normal working point. No significant increase in spark r ate or strip loss rate was detected and the chambers operated stably. The d etector efficiencies and imaging capabilities were also investigated. The M SGC design features and the assembly and test methodologies that enabled us to achieve these results are reported. (C) 2001 Elsevier Science B.V. All rights reserved.