Micromegas chambers for the experiment ATLAS at the LHC (A Brief Overview)
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cromegas Chambers for the Experiment ATLAS at the LHC (A Brief Overview) A. L. Gongadze Dzhelepov Laboratory of Nuclear Problems, Joint Institute for Nuclear Research, Dubna, 141980 Russia E. Andronikashvili Institute of Physics, Tbilisi, 0177 Georgia email: [email protected] Abstract—The increase in luminosity and energy of the Large hadron collider (LHC) in the next upgrade (Phase1) in 2018–2019 will lead to a significant increase in radiation load on the ATLAS detector, primarily in the areas close to the interaction point of the LHC proton beams. One of these regions is the Small Wheel of the ATLAS Muon Spectrometer. It is planned to be replaced with the New Small Wheel that will have Micromegas chambers as main coordinate detectors. The paper gives an overview of all existing types of Micromegas detectors with special focus on the Micromegas chambers for the ATLAS detector upgrade. DOI: 10.1134/S1063779616020027
1. INTRODUCTION Gaseous particle detectors are one of the most widespread types of detectors in use in nuclear physics [1, 2]. First detectors of this kind appeared early in the XX century when the singlewire proportional counter and the GeigerMueller counter were invented [3]. These can be considered to be the ancestors of all modern gaseous detectors and for decades were one of the main means of studying ionizing radiation. A wide application of the counters was limited by the absence of suitable multichannel electronics, and by 1968 all “data readout” systems were optical in nature: photo graphic emulsions, the Wilson chamber, the bubble chamber, the spark chamber, Geiger counter hodo scopes and so on. Information from these detectors was stored in a photographic film, which was later ana lyzed frame by frame. A breakthrough was possible in 1968 when the multiwire proportional chamber (MWPC) was invented by G. Charpak [4]. He showed that each anode wire of an array densely positioned in a single chamber can act as an indepen dent proportional counter. Furthermore, the level of semiconductor microelectronics of that time made it possible to provide each channel (signal wire) of a chamber with a dedicated amplifier integrated with the chamber, which enabled mass production of coor dinate detectors based on the proportional chamber. Due to it’s excellent—by the standards of that time—accuracy in determination of position and count rate, the MWPC was quickly adopted and stim ulated new generations of detectors: drift and time projection chambers [5]. However, the MWPC has two significant limita tions, that is, the spatial resolution and count rate. The wires cannot be located very close to each other due to
mechanical and electrostatic problems, and thus ions can’t be collected sufficiently fast. To cope with this problem, A. Oed proposed the microstrip gaseous chamber in 1985 (MSGC) [6]. The MSGC was the first of a new breed of detectors, known as micro pat tern gas detectors (MPGD). MSGC The electrode structure of a microstrip gas cham ber is shown in Fig. 1. The MSGC, which cons
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