Progress with the gas electron multiplier

Offering position accuracies of few tens of microns and rate capabilities close to a MHz mm/sup -2/, detectors using the gas electron multiplier (GEM) as amplifying element are attractive whenever a precise knowledge of the energy loss topology is required. Moreover, they are robust and easy to manufacture. Cascading two or more GEM foils permits to achieve larger gains and reliable operation in harsh operating conditions. We discuss the operating principles and the major performances of the new devices, particularly in view of their possible use for particle identification in transition radiation and Cherenkov ring imaging detectors. (26 refs).