Abstract:
AMBER is a new fixed-target experiment at CERN’s SPS, designed to investigate fundamental properties of hadrons. In the next years, measurement campaigns are planned which aim to measure the proton charge radius, antiproton production cross sections and Drell-Yan processes. In the predecessor experiment, Gas Electron Multiplier (GEM)-based detectors have been used since 2001 for precise tracking close to the beam. The requirements of the new measurements planned for AMBER, free-streaming readout and higher rate capability for strips in the central region, demand an upgrade of the existing COMPASS GEM tracking system. During the commissioning phase of new 30×30 cm2 triple-GEM tracking detectors, a significantly higher gain was measured at a certain position in the detector, compared to the rest of the active area. This hot spot appeared in all new detectors in the lab and at a test beam at the SPS. Large inhomogeneities in the gain distribution can potentially lead to discharges, threatening stable operation of the detector or even damaging it, or to inefficiencies in lower gain regions. In this talk, I will present systematic investigations towards the cause of this effect and discuss possible solutions.