Evaluation and reduction of ion back-flow in multi-GEM detectors

In gaseous photomultipliers, avalanche generated ions back-flowing to the photocathode can drastically limit the detector operation and lifetime. This is especially the case for photocathodes with low electron emission threshold, where impinging ions induce ion feedback effects by secondary electron emission. sent ways of reducing ion-backflow to the photocathode, and thus suppress ion-feedback effects in multi-stage Gas Electron Multiplier detectors. We studied the effect of the various electric fields on the ion transport in the detector and present our results on active ion gating with a dedicated gating electrode.