We describe the operating characteristics of open and closed-end gas electron multipliers (GEMs)
in terms of the electron collection eciency and the gas gain. Since the eective GEM gain is
typically smaller than the absolute GEM gain due to the trap...
We describe the operating characteristics of open and closed-end gas electron multipliers (GEMs)
in terms of the electron collection eciency and the gas gain. Since the eective GEM gain is
typically smaller than the absolute GEM gain due to the trapping of avalanche electrons at the
bottom GEM electrode, we performed electric-eld simulations to better understand this effect and
to identify methods to eliminate it. Other aspect of GEM performance, the leakage current and the
short-term gain stability, are also presented..