Multi-GEM Detectors in High Particle Fluxes

¹ CERN, European Organization for Nuclear Research, 1211 Geneva, Switzerland
² Technische Universität Wien, Atominstitut, Stadionallee 2, 1020 Vienna, Austria
³ Uludağ University, Department of Physics, 16059 Bursa, Turkey
⁴ ESS, European Spallation Source, 22100 Lund, Sweden

^a e-mail: patrik.thuiner@cern.ch
^b e-mail: filippo.resnati@cern.ch

Published online: 21 February 2018

Abstract

Gaseous Electron Multipliers (GEM) are well known for stable operation at high particle fluxes. We present a study of the intrinsic limits of GEMdetectors when exposed to very high particle fluxes of the order of MHz/mm2. We give an interpretation to the variations of the effective gain, which, as a function of the particle flux, first increases and then decreases. We also discuss the reduction of the ion back-flow with increasing flux. We present measurements and simulations of a triple GEM detector, describing its behaviour in terms of accumulation of positive ions that results in changes of the transfer fields and the amplification fields. The behaviour is expected to be common to all multi-stage amplification devices where the efficiency of transferring the electrons from one stage to the next one is not 100%.