Development of a triple GEM UV-photon detector operated in pure CF4 for the PHENIX experiment

Results obtained with a triple Gas Electron Multiplier (GEM) detector operated in pure CF4 with and without a reflective CsI photocathode are presented. The detector operates in a stable mode at gains up to 104. A deviation from exponential growth starts to develop when the total charge exceeds ∼4×106 e leading to gain saturation when the total charge is ∼2×107 e and making the structure relatively robust against discharges. No aging effects are observed in the GEM foils after a total accumulated charge of ∼10 mC/cm2 at the anode. The ion back-flow current to the reflective photocathode is comparable to the electron current to the anode. However, no significant degradation of the CsI photocathode is observed for a total ion back-flow charge of ∼7 mC/cm2.