Aging of large-area CsI photocathodes for the ALICE HMPID prototypes

The ALICE High-Momentum Particle IDentification RICH detector is equipped with CsI photocathodes (PCs) in a MWPC for the detection of Cherenkov photons. The long-term operational experience with large-area CsI PCs is described. The RICH prototypes have shown a very high stability of operation and performance at a gain of 105 and with rates up to 2x104 cm-2 s-1. When exposure to air is avoided, no degradation of the CsI quantum efficiency has been observed on PCs periodically exposed to test beams over 7 years, corresponding to local integrated charge densities of ∼1 mC/cm2. The results of limited exposures to oxygen and humidity are also presented