The triple GEM detector as beam monitor for relativistic hadron beams

A triple GEM detector was tested at the CERF facility at CERN as an on-line beam imaging monitor and as a counting reference device. It was exposed to a 120 GeV/c positively charged hadron beam (approximately 2/3 pions and 1/3 protons), which hits a copper target generating a wide spectrum of different kinds of particles used for various experiments. The flux of beam particles ranged over three orders of magnitude, from 8·10⁴ s⁻¹ to 8·10⁷ s⁻¹. The profile of the beam acquired with the GEM was compared to the one measured with a MWPC and no saturation was observed. In addition, the count rate measured with the GEM was compared to the one measured with an Ionization Chamber, which is routinely used for monitoring the beam intensity. Another way of monitoring the intensity of the beam was also explored, which is based on the total current driven from the GEM foils. The digital readout allows making a 2D online image of the beam for the alignment with the copper target in the CERF facility. A low residual activation of the detector was observed shortly after irradiation.