Limits to proportionality in the double GEM detector

Abstract We have examined the operation of a GEM, double GEM and GEM+MGC combination using argon/DME 90/10, 60/40, 40/60, 20/80, xenon/DME 90/10, xenon/CO 2 90/10 as well as pure argon and pure xenon. In a cascaded GEM configuration, large gains are recorded, around 10 5 in argon/DME 90/10. Energy resolution is