Results obtained with a triple 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 10^4. A deviation from exponential growth starts to
develop when the total charge exceeds ~ 4 10^6 e leading to gain saturation
when the total charge is ~ 2 10^7 e and making the structure relatively robust
against discharges. No aging effects are observed in the GEM foils after a
total accumulated charge of ~ 10 mC/cm^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 CsI photocathode is
observed for a total ion back-flow charge of ~ 7 mC/cm^2.Comment: 14 pages, 11 figures, Submitted to NIM