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.
Highlights
For more than a decade, micro-pattern gaseous detectors (MPGDs), such as the GEM [1] and the Micromegas [2], have proven to be valuable tools for high-energy physics thanks to their good energy, time and position resolutions, their high rate capability, their low spark rate and their ability to limit ion backflow
MPGDs are found in virtually all high energy physics experiments [3,4,5,6]
They appear as most promising technologies for the LHC instrumentation upgrade [7,8,9] and are considered as part of the detection system associated to the future International Linear Collider (ILC) facility [10]
Summary
For more than a decade, micro-pattern gaseous detectors (MPGDs), such as the GEM [1] and the Micromegas [2], have proven to be valuable tools for high-energy physics thanks to their good energy, time and position resolutions, their high rate capability, their low spark rate and their ability to limit ion backflow. Active reaction targets for radioactive-beam reactions are another example of applications that are attracting much of attention [16,17,18] These devices are based on TPC technology, where the tracking gas is used simultaneously as the target of nuclear reactions. This paper proposes a method ideally suited to get such data Compared to the traditional use of a radioactive source or a charged particles beam, this method provides a direct measurement of the absolute gain and the relative gain variance but requires an optimised test-bench, in terms of detector mechanics and electronics signal-to-noise ratio, to enable single electron detection in a wide range of electric field, down to gains as low as a few 103.
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