Further developments and beam tests of the gas electron multiplier (GEM)

We describe the development and operation of the Gas Electron Multiplier (G EM), a thin insulating foil metal-clad on both sides and perforated by a re gular pattern of small holes. The mesh can be incorporated into the gas vol ume of an active detector to provide a first amplification channel for elec trons, or used as stand alone. We report on the basic properties of GEMs ma nufactured with different geometries and operated in several gas mixtures a s well as on their long-term stability after accumulation of charge equival ent to several years of operation in high-luminosity experiments. Optimized GEMs reach gains close to 10000 at safe operating voltages, permitting the detection of ionizing tracks, without other amplifying elements, on a simp le Printed Circuit Board (PCB), opening new possibilities for detector desi gn. (C) 1998 Published by Elsevier Science B.V. All rights reserved.