MICROMEGAS: A high-granularity position-sensitive gaseous detector for high particle-flux environments

We describe a novel structure for a gaseous detector that is under development at Saclay. It consists of a two-stage parallel-plate avalanche chamber of small amplification gap (100 mu m) combined with a conversion-drift space. It follows a fast removal of positive ions produced during the avalanche development. Fast signals (less than or equal to 1 ns) are obtained during the collection of the electron avalanche on the anode microstrip plane. The positive ion signal has a duration of 100 ns. The fast evacuation of positive ions combined with the high granularity of the detector provide a high rate capability. Gas gains of up to 10(5) have been achieved.