Construction and Calibration of a Setup for Micro-Pattern Gaseous Detectors Using UV Laser Photoelectrons

After the discovery of the Higgs boson at the Large Hadron Collider (LHC) in summer 2012, the properties and couplings of the newly found particle need to be determined. To deliver the necessary amount of data, the LHC will raise its luminosity significantly and new detector technologies are needed that can withstand the demands due to the increased particle flux. New types of gaseous detectors like Micro Pattern Gaseous Detectors (MPGD) and especially the Micromegas that are foreseen for the ATLAS Muon New Small Wheel upgrade, show very good rate capabilities so far. A test setup to investigate the properties of Micromegas has been designed and built. The setup uses photoelectrons created by a UV laser in the drift volume as the primary charge to probe the detector. The creation points and times are precisely known and the setup is independent of test beams. It includes a reference measurement system based on multi-wire technology and has been commissioned and fully calibrated. A Micromegas test candidate unit with 8 different readout geometry zones and an additional cathode layer has been designed and the performance of a prototype was intensively investigated. Gain studies as well as drift and diffusion studies have been carried out successfully. Studies and Garfield simulations regarding the discharge behavior of the Micromegas test candidate and the supplementary cathode on the bottom of the detector have been carried out and indicate a controllable influence on the electric field configuration in the amplification area by the additional potential.