Triple Gas Electron Multiplier (GEM) detectors will be used as a tracking device in the first two stations of CBM MUon CHamber (MUCH), where the maximum particle rate is expected to reach ~1 MHz/cm2 for central Au-Au collisions at 8 AGeV. Therefore, the stable operation of the detector is very important. Discharge probability has been measured of a single mask triple GEM detector at the CERN SPS/H4 beam-line facility with a pion beam of ~150 GeV/c and also in an environment of highly ionizing shower particles. The spark probability as a function of gain has been studied for different particle rates. The details of the experimental setup, method of spark identification and results are presented in this paper.
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