Studies of alternative gases and wavelength shifters for optically read out MicroPattern Gaseous Detectors

Gaseous detectors allow the detection of ionising particle, and they are widely used in the particle physics experimentation. The invention of electronically read out gaseous detectors by Georges Charpak in 1968 revolutionized the use of detectors for tracking by using electrical signals with an increased granularity of readout channels. This invention lead to the creation of Gas Detectors Development group at CERN. After the initial invention, they have been further developed into more sophisticated devices with higher spatial and time resolutions. Gaseous detectors are used in many large scale particle physics, including LHCb, COMPASS and TOTEM experiments at CERN. After many successful implementations of wire-based detectors, the exploitation of advanced structuring processes lead to the introduction of MicroPattern Gaseous Detectors which overcome many of limitations of Multiwired proportional chambers, including the exposure of fragile electrodes to high energy fields which are needed for reaching high enough gains to detect small ionization yields. The gaseous detectors are based on the process of gas ionization. An incoming particle ionizes gas, producing electrons and ions, which are separated with an applied electric field, inducing signal on the anode by the electrons and on the cathode by the ions. In addition to detecting electrons, also optical readout is possible, as also photons are produced in the ionization process due to spontaneous emission. The aim of this study is to examine the optical readout of gaseous detectors and the gases used within them. Tetrafluoromethane (CF4) is a common gas for optical readout setups due to its unique properties, that are presented later. However, it is a strong greenhouse gas. The focus is to study alternative gases and methodologies to replace the CF4. This study is divided into two parts. The the first part focuses on studying the transmission properties of potential alternative gases. The focus is on the UV wavelength range, as most noble gases scintillate in that wavelength range. The second part focuses on the spatial resolution of the detector, considering different amplification structures and gaps between the amplification structure and the solid wavelength shifter.