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Understanding avalanches in a Micromegas from single-electron response measurement

Abstract : Avalanche fluctuations set a limit to the energy and position resolutions that can be reached by gaseous detectors. This paper presents a method based on a laser test-bench to measure the absolute gain and the relative gain variance of a Micro-Pattern Gaseous Detector from its single-electron response. A Micromegas detector was operated with three binary gas mixtures, composed of 5% isobutane as a quencher, with argon, neon or helium, at atmospheric pressure. The anode signals were read out by low-noise, high-gain Cremat CR-110 charge preamplifiers to enable single-electron detection down to gain of 5× 103 for the first time. The argon mixture shows the lowest gain at a given amplification field together with the lowest breakdown limit, which is at a gain of 2×104 an order of magnitude lower than that of neon or helium. For each gas, the relative gain variance f is almost unchanged in the range of amplification field studied. It was found that f is twice higher (f~0.6) in argon than in the two other mixtures. This hierarchy of gain and relative gain variance agrees with predictions of analytic models, based on gas ionisation yields, and a Monte-Carlo model included in the simulation software Magboltz version 10.1.
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Submitted on : Tuesday, March 24, 2015 - 11:09:59 AM
Last modification on : Wednesday, October 14, 2020 - 3:59:26 AM

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T. Zerguerras, B. Genolini, F. Kuger, M. Josselin, A. Maroni, et al.. Understanding avalanches in a Micromegas from single-electron response measurement. Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment, Elsevier, 2014, 772, pp.76-82. ⟨10.1016/j.nima.2014.11.014⟩. ⟨in2p3-01134723⟩



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