Studies on Fluorine-based impurities production in Triple-GEMs operated with CF4-based gas mixture

摘要

One of the primary elements influencing gaseous detectors operation is the purity of the gas mixture. Its quality can be undermined by the presence of impurities, that could be created in the gas system or from the detector itself. Gaseous detectors operated with Freon-based gas mixtures are subject to the formation and accumulation of the products of molecule breaking phenomena, happening when the gas is exposed to radiation, and enhanced by the presence of high electric field in the gas volume. The liberation of highly reactive products could be critical as they could either create polymerized deposits or cause material etching, that could compromise detector performance and accelerate aging processes. This work focuses on the F^{− impurities production in Triple-GEMs detectors, largely implemented in LHC experiments, that can be operated with CF4-based gas mixture. The phenomenon is studied in a LHC-like gas system, exposing detectors to high-rate gamma irradiation thanks to the intense 137Cs source provided by the CERN Gamma Irradiation Facility (GIF++). Fluorine-based impurities production is studied in relation to operation under different irradiation rates, detector and gas system conditions. A complete overview of the results obtained at GIF++ is presented.}