First results on the GEM operated at low gas pressures

We report on the properties of the Gaseous Electron Multiplier (GEM) operated at 10–40 Torr isobutane and methane. We found stable operation at gains of a few thousand, fast response and effective photon-feedback reduction. The transmission of single electrons through the GEM apertures was studied. Ion-induced feedback, from a wire chamber following the GEM, was found to limit the total two-stage multiplication at high GEM gains. A stable double-GEM operation with reduced ion-feedback was demonstrated. Some applications are discussed.