Abstract
The ATLAS collaboration has chosen the Micromegas technology along with the small-strip Thin Gap Chambers for the upgrade of the inner muon station in the high-rapidity region, the so called New Small Wheel upgrade project. It will employ eight layers of Micromegas and eight layers of small-strip Thin Gap Chambers per wheel. The New Small Wheel project requires fully efficient Micromegas chambers, able to cope with the maximum expected rate of 15 kHz/cm 2 featuring single plane spatial resolution better than 100 μm. The Micromegas detectors will cover a total active area of ~ 1200 m 2 and will be operated in a moderate magnetic field (≤ 0.3 T). Moreover, together with their precise tracking capability the New Small Wheel Micromegas chambers will contribute to the ATLAS Level-1 trigger system. Several studies have been performed on small (10 × 10 cm 2 ) and medium (1 × 0.5 m 2 ) size prototypes using medium (1 − 5 GeV/c) and high momentum (120 – 150 GeV/c) hadron beams at CERN. A brief overview of the results obtained is presented.
Highlights
The upgrade of the Large Hadron Collider (LHC) at CERN foresees a luminosity increase by a factor 5
The results demonstrate the excellent performance of the MM chambers that fulfil the requirements of the New Small Wheel system (NSW) project in terms of hit reconstruction accuracy and efficiency
After an intensive R&D phase, which begun in 2007, the MM technology has evolved significantly over the last years and it was approved as one of the technologies that will be used in the NSW upgrade project of the ATLAS experiment
Summary
The upgrade of the Large Hadron Collider (LHC) at CERN foresees a luminosity increase by a factor 5. The electron avalanche takes place in the thin amplification region in about a nanosecond, resulting in a fast pulse on the readout strip [7]. Sparks may damage the detector structure or the readout electronics and lead to large dead times as a result of high voltage breakdown. By adding a layer of resistive strips on top of a thin insulator directly above the readout electrode, as shown, the MM becomes spark-insensitive. By adding the resistive protection some fraction of the signal amplitude is lost but the chamber can be operated at higher gas gain because sparking is reduced by about three orders of magnitude and the effect is only locally constrained in a small region of the detector [9]. Resistive MM chambers can be efficiently operated in a high-rate environment as was demonstrated by testing small resistive prototypes inside the ATLAS experiment with particle rates up to 80 kHz/cm2 [10, 11]
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