Quality Assurance of Gas Electron Multiplier Detector

Abstract

Gas Electron Multiplier (GEM) detectors are special of position sensitive gas filled detectors used in several particle physics experiments. They are capable of sub- millimeter spatial resolution and energy resolution (FWHM) of the order of 20%. GEM detectors can operate with rates up to 50 kHz/mm2, withstand radiation excellently and can be manufactured up to square meter sizes.

This thesis describes the Quality Assurance (QA) methods used in the assembly of 50 GEM detectors for the TOTEM T2 telescope at the LHC at CERN. Further development of optical QA methods used in T2 detector assembly lead into development of a unique large-area scanning system capable of sub-µm resolution. The system, its capability and the software used in the analysis of the scans are described in detail.

A correlation was found between one of the main characteristics of the detector, the gas gain, and the results of the optical QA method. It was shown, that a qualitative estimation of the gain can be made based on accurate optical measurement of the microscopic features of the detector components. Ability to predict the performance of individual components of the detectors is extremely useful in large scale production of GEM based detectors.