Performances and Ageing Study of Resistive-Anodes Micromegas Detectors for HL-LHC Environment

With the tenfold luminosity increase envisaged at the HL-LHC, the background (i.e., photons, neutrons, <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$\ldots$</tex> </formula> ) and the event pileup probability are expected to highly increase in proportion in the different experiments, especially in the forward regions, for instance the muons chambers of the ATLAS detector. Detectors based on the Micromegas principle should be good alternatives for the detector upgrade in the HL-LHC framework because of its good spatial <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex Notation="TeX">$(&lt; 100\mu{\hbox{m}})$</tex></formula> and time (few ns) resolutions, high-rate capability, radiation hardness, good robustness, and the possibility to build large areas. The aim of this study is to demonstrate that it is possible to reduce the discharge probability and protect the electronics by using a resistive anode plane in a high-flux hadrons environment. Several prototypes of <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$10 \times 10~{\hbox{cm}}^{2}$</tex></formula> , with different pitches (0.5–2 mm) and different resistive layers have been tested at CERN <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex Notation="TeX">$(\pi^{+}@{\rm SPS})$</tex></formula> . Several tests have been performed with a telescope at different voltages to assess the performance of the detectors in terms of position resolution and efficiency. The spark behavior in these conditions has also been evaluated. Resistive coating has been shown to be a successful method to reduce the effect of sparks on the efficiency of micromegas. A good spatial resolution <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex Notation="TeX">$(\sim 80\ \mu{\hbox{m}})$</tex></formula> can be reached with a resistive strip coating detector of 1-mm pitch, and a high efficiency <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$( &gt; 98\%)$</tex></formula> can be achieved with resistive-anode micromegas detector. An X-rays irradiation has also been performed, showing no ageing effect after more than 21 days exposure and an integrated charge of almost 1C.