Tests of eco-friendly gas mixtures in GEM based detectors with optical readout

Modern imaging sensors can be used to detect the scintillation light produced in Micro Pattern Gaseous Detectors (MPGDs) during electron avalanche multiplication. Gas mixtures with scintillation light spectra compatible with the quantum efficiency of CCD or CMOS cameras, can be used to implement an optical readout and to build 2D images of the events. Cygno project aims at developing an optical Time Projection Chamber (TPC) for directional dark matter searches and neutrino scattering measurements. A triple GEM stack is used as amplification stage, with the light produced during the multiplication process being detected by a sCMOS camera. The TPC is operated with a mixture of Helium (He) and Tetrafluoromethane (CF4). Recently many freon gases, as the CF4, have been banned due to their high impact on the atmosphere. Our group has started a study to use eco-friendly gases to replace the CF4 in such applications. The setup used to collect data and preliminary results in terms of charge gain and scintillation yield will be presented for some of the more interesting ecological gas mixtures available.