Micro-pattern gas detectors

Micro-strip gas chambers, with their excellent localization properties, high-rate capability and good granularity, have been adopted by many experiments in particle physics. Two recurrent problems, however, have been reported: a slow degradation under sustained irradiation (or aging), and the rare but devastating occurrence of discharges. New breeds of detectors aim at improving on these crucial points; the micro-dot, CAT, micromegas, the gas electron multiplier are examples. Very performing, they are moreover robust and reliable. Two-stage devices, making use of a gas electron multiplier as first element, permit larger gains in presence of high rates and heavily ionizing tracks. Possible promising future developments in the field are outlined.