High rate behavior and discharge limits in micro-pattern detectors

We present and discuss a set of systematic measurements, carried out with g aseous proportional micro-pattern detectors, in order to assess their maxim um gain when irradiated with high-rate soft X-rays and heavily ionizing alp ha particles. The inventory of detectors tested includes: micro-strips, mic romegas, micro-dot, gas electron multiplier, CAT (compteur a trous), trench (or groove), micro-CAT (or WELL) detectors, as well as systems with two el ements of gaseous amplification in cascade. We confirm the general trend of all single-stage detectors to follow Raether's criterion, i.e. a spontaneo us transition from avalanche to streamer, followed by a discharge, when the avalanche size reaches a value of a few 10(7); a noticeable exception is t he micro-dot counter holding more than 10(8). In multiple structures, where the gain is shared between two devices in cascade, the maximum overall gai n under irradiation is increased by at least one order of magnitude; we spe culate this to be a consequence of a voltage dependence of Raether's limit, larger for low operating potentials. Our conclusion is that only multiple devices can guarantee a sufficient margin of reliability for operation in h arsh LHC running conditions. (C) 1999 Elsevier Science B.V. All rights rese rved.