A Gas Electron Multiplier (GEM) placed inside a liquid argon neutrino detector may be used as a low-background single electron detector–complementing the standard Time Projection Chamber (TPC) techniques for detecting and tracking neutrino interactions. GEMs are a relatively new type of detection method and our group has set out to reseach and develop GEM technology to eventually implement in a LArTPC.
GEMs are composed of densely perforated layers of copper surrounding a thin sheet of insulation.
As a voltage difference is applied between the two layers of copper, a large electric field is created within the holes. The picture below shows the electric field lines of the GEM. An electron reaches the high electric field of the GEM hole and goes through a gas ionization avalanche process. The electron signal is amplified and more electrons come out from the top of the GEM. Signal collection may take place on the top of the GEM or the electrons may continue on to an XY grid in order for spatial resolution to be obtained.