Operation of a triple GEM detector with CsI photocathode in pure CF/sub 4/

Results obtained with a triple GEM detector operated in pure CF/sub 4/ with and without a reflective CsI photocathode are presented. The detector operates in a stable mode at gains up to 10/sup 4/. A deviation from exponential growth starts to develop when the total charge exceeds /spl sim/ 4 /spl times/ 10/sup 6/ e leading to gain saturation when the total charge is /spl sim/ 2 /spl times/ 10/sup 7/ e and making the structure relatively robust against discharges. No aging effects are observed in the GEM foils after a total accumulated charge of /spl sim/ 10 mC/cm/sup 2/ 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 CA photocathode is observed for a total ion back-flow charge of /spl sim/ 7 mC/cm/sup 2/.