Ion-induced effects in GEM & GEM/MHSP gaseous photomultipliers for the   UV and the visible spectral range
  We report on the progress in the study of cascaded GEM and GEM/MHSP gas avalanche photomultipliers operating at atmospheric pressure, with CsI and bialkali photocathodes. They have single-photon sensitivity, ns time resolution and good localization properties. We summarize operational aspects and results, with the highlight of a high-gain stable gated operation of a visible-light device. Of particular importance are the results of a recent ion-backflow reduction study in different cascaded multipliers, affecting the detector's stability and the photocathode's liftime. We report on the significant progress in ion-blocking and provide first results on bialkali-photocathode aging under gas multiplication. 
A. Breskin, D. Mormann, A. Lyashenko, R. Chechik, F.D. Amaro, J.M.   Maia, J.F.C.A. Veloso, and J.M.F. dos Santos