| GEM - A novel gaseous particle detector (2005) | |||||||||
Abstract | |||||||||
| The work carried out within the framework of this Ph.D. deals with the construction of gaseous prototype detectors using Gas Electron Multiplier electrodes for the amplification of charges released by ionizing particles. The Gas Electron Multiplier (GEM) is a thin metal-clad polymer foil, etched with a high density of narrow holes, typically 50-100mm-2. On the application of a potential difference between the conductive top and bottom sides each hole acts as independent proportional counter. This new fast device permits to reach large amplification factors at high rates with a strong photon and ion-mediated feedback suppression due to the avalanche confinement in the GEM-holes. Here, in particular studies have been performed, which should prove, that the GEM-technology is applicable for an efficient measurement of single Cherenkov photons. These UV-photons can be detected in different ways. An elegant solution to develop large area RICH-detectors is to evaporate a pad-segmented readout-cathode of a multi-wire proportional chamber with a thin layer of CsI (typically 300nm). This approach has advantages compared to other possibilities of detecting Cherenkov photons (e.g.: photosensitive gases, arrays of PMTs or HPDs). The subject of this thesis was the investigation of GEM-detectors with respect to RICH applications. This work contains the construction process of photon detectors based on the novel GEM-technology by using CsI as a photon converter. These detectors permit to efficiently record and localize single photoelectrons. The first Au-plated GEM, in a cascade of three or four, is coated with a photosensitive layer, to provide efficient and fast single photon detection, with excellent position resolution. General performances of a CsI-coated multi-GEM detector are described as well as the novel readout method, which is achieved by the so called HEXABOARD. This board consists of a matrix of interconnected hexagonal pads that permit an ambiguity-free reconstruction of multi-photon events, which is an essential requirement for RICH applications. Each single channel is connected to charge sensitive preamplifier (HARP-type) and afterwards to the ALTRO FEE, which is based on the ALTRO chip developed for the ALICE experiment. The recorded analog signals are digitized by 10 bit ADC with a 25MHz sampling rate. | |||||||||
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