High gain operation of GEM in pure argon

We study the operation of the Gas Electron Multiplier (GEM) in pure Ar, in comparison to that in Ar–CO2 mixture. In pure Ar, high GEM gains, of above 700 and 3000 for single and double GEM structures, respectively, have been obtained. It is observed that the GEM effective gain and its charging-up are strongly affected by electric field values above and below the GEM. Applications to the development of non-ageing gas photomultiplier are discussed.