Development of a fast gaseous detector: ‘Micromegas’

• Published in: Nuclear instruments & methods in physics research. Section A, Accelerators, spectrometers, detectors and associated equipment Accelerators, spectrometers, detectors and associated equipment, 1999-02, Vol.423 (1), p.32-48
• Main Authors: Barouch, G, Bay, A, Bouchigny, S, Charpak, G, Derré, J, Didierjean, F, Faivre, J.-C, Giomataris, Y, Kochowski, C, Kunne, F, Le Goff, J.-M, Lehar, F, Lemoigne, Y, Loucatos, S, Lugol, J.-C, Magnon, A, Mayer, B, Perroud, J.-P, Platchkov, S, Puill, G, Rebourgeard, Ph, Terrien, Y, Thers, D, Zaccone, H
• Format: Article
• Language: English
• ISSN: 0168-9002; 1872-9576
• DOI: 10.1016/S0168-9002(98)01265-0

Several 15×15 cm 2 gaseous Micromegas chambers (MICROMEsh GAseous Structure) which consist of a conversion gap and an amplification gap separated by a thin grid have been extensively tested in low-intensity 10 GeV/c pion beam and high-intensity (up to 5×10 5 Hz/ mm 2) 100 GeV/c muon beam. The detector behaviour has been studied with respect to many parameters: conversion gaps of 1 and 3 mm, amplification gaps of 50 and 10 μm, an external magnetic field and many different filling gases. So far no effect of the magnetic field up to 1.3 T has been observed. The gas mixture argon + cyclohexane appears to be very suitable with gains above 10 5 and a full-efficiency plateau of 50 V at 340 V. With a conversion gap as small as 1 mm and an electronics with a threshold at 5000 electrons the efficiency reaches 96%. With the addition of CF 4 a time resolution of 5 ns (RMS) has been obtained. A spatial resolution better than 60 μ m has been observed with anode strips of 317 μ m pitch and was explained by transverse diffusion in the gas. Simulations show that with a pitch of 100 μ m and the appropriate gas a resolution of 10 μ m is within reach. This development leads to a new generation of cheap position-sensitive detectors which would permit high-precision tracking or vertexing close to the interaction region, in very high-rate environments.