Radiation hardness and ageing properties of small gap plus GEM chambers

Large size small gap chambers (SGC) equipped with gas electron multiplier (GEM) were exposed to a low-energy hadron beam to characterize their hardness to highly ionizing radiations. During the test, rate and effect of discharges induced by highly ionizing particles were studied as a function of the cathode and GEM voltages. We propose an optimization of the voltages to safely operate the detectors at the largest signal-to-noise ratio. In a second test, the ageing properties of the chambers were measured up to a 5 mC/cm integrated charge, induced by an X-ray beam. clude from the two measurements on the good reliability and possible improvements of the SG plus GEM Chambers for long term use in a harsh radiation environment.