Gas Electron Multipliers for the Antiproton Decelerator

The new beam pro� le measurement for the Antiproton Decelerator (AD )a tCERNis based on a single Gas Electron Multiplier (GEM) with a 2D readout structure. This detec- tor is very light (∼ 0.4% X0), and measures horizontal and vertical pro� les directly in one plane. This overcomes the problems previously encountered with multi-wire propor- tional chambers for the same purpose, where beam inter- actions with the detector severely affect the obtained pro- � les. A prototype was installed and successfully tested in late 2010, with another� ve detectors now installed in the ASACUSA and AEGIS beam lines. This paper will provide a detailed description of the detector and discuss the results obtained.