Experiences with a pre-series of Micro Strip Gas Counters with Gas Electron Multipliers for high rate applications

Micro strip gas chambers (MSGCs) are promising candidates for large scale applications. They combine a good spatial resolution with high granularity and low cost. As a possible extension of the plain MSGC, a Gas Electron Multiplier (GEM) foil may be implemented into the detector in order to increase the safety of operation. It was planned to equip the outer part of the tracking system of the Compact Muon Solenoid (CMS) experiment at the future Large Hadron Collider (LHC) at the Centre de Recherche Nucleaire (CERN) with MSGCs. In the barrel part of the tracker, plain MSGCs were to be used. For the forward part, the MSGC+GEM technology was envisaged. This thesis describes the assembly and test of a pre-series of 18 fully functional MSGC+GEM forward detector modules to determine their radiation hardness and their readiness for mass production. Five of the modules were built at Aachen, thirteen more at the 'Institut für Experimentelle Kernphysik' in Karlsruhe. For the pre-series, two different types of GEM foils were used: 17 foils were wet etched (by a workshop at CERN) in a procedure that resulted in double conical holes. One foil was plasma-etched (by Würth Elektronik GmbH) which has lead to an underetching of the GEM-holes. In 1999 it was not clear, whether the MSGC or MSGC+GEM technology are suited to withstand the high rate irradiation at the LHC. To test the radiation hardness of the 18 modules, they were taken to the the Paul Scherrer Institut to be irradiated for 376 hours under LHC-like conditions in the so-called 'mf2 milestone'. 16 of the detectors were found to be of good quality and were chosen to participate in the milestone. They showed stable operation during the 376 hours of irradiation, loosing less than 0.14% of the readout strips. This can be extrapolated to a degradation of spatial resolution in less than 5% of the active surface of the CMS outer tracker within 10 years of operation. Thus it could be shown that the MSGC+GEM technology is well suited for the operation in CMS-like experiments. The five Aachen-built modules, among them the one with the underetched GEM, have further been tested in a laboratory experiment. There the uniformity of the detectors was determined in order to find out whether a mass production of MSGC+GEMs is feasible. In addition, signal shaping and transparency were measured in different gas mixtures, namely Ne/DME, Ar/CO2 and Ne/DME/CO2. It was found that only the underetched foil can be operated under optimal conditions with all gas mixtures under test. For the double conical GEM, a fast gas like Ar/CO2 is required in order to operate on the transparency plateau with the readout electronics used. Finally, several problems that may arise in a detector mass production were identified so that solutions can be found in the future. Even though the MSGC+GEM technology was rejected for the CMS experiment, this thesis proves that the detectors are suited to equip large scale, high rate experiments.