Micromegas Research Articles

A novel diamond-like carbon based photocathode for PICOSEC Micromegas detectors

The PICOSEC Micromegas (MM) detector is a precise timing gaseous detector based on a MM detector operating in a two-stage amplification mode and a Cherenkov radiator. Prototypes equipped with cesium iodide (CsI) photocathodes have shown promising time resolutions as precise as 24 picoseconds (ps) for Minimum Ionizing Particles. However, due to the high hygroscopicity and susceptibility to ion bombardment of the CsI photocathodes, alternative photocathode materials are needed to improve the robustness of PICOSEC MM. Diamond-like Carbon (DLC) film have been introduced as a novel robust photocathode material, which have shown promising results. A batch of DLC photocathodes with different thicknesses were produced and evaluated using ultraviolet light. The quantum efficiency measurements indicate that the optimized thickness of the DLC photocathode is approximately 3 nm. Furthermore, DLC photocathodes show good resistance to ion bombardment in aging test compared to the CsI photocathode. Finally, a PICOSEC MM prototype equipped with DLC photocathodes was tested in muon beams. A time resolution of around 42 ps with a detection efficiency of 97% for 150 GeV/c muons were obtained. These results indicate the great potential of DLC as a photocathode for the PICOSEC MM detector.

The New Small Wheel Trigger for the ATLAS experiment

The ATLAS New Small Wheel (NSW) Muon spectrometer upgrade, completed in 2022, was the largest Phase I detector upgrade among LHC experiments. The NSW enhances triggering in the endcap region (1.3<|η|<2.4) by confirming muons from the Interaction Point (IP) and rejecting fake contributions. It also improves muon tracking with 2.5 million high-resolution channels across 16 layers. The NSW Trigger, based on small-strip Thin Gap Chambers (sTGC) and Micromegas (MM) technologies, provides Level-1 triggers at every Bunch Crossing (BC) with a fixed low latency (44 BC). Integrated into ATLAS in 2023, the NSW Trigger significantly reduces fake rates and overall readout deadtime. The custom electronics of the NSW Trigger system efficiently collect, process, and trigger on IP muons, focusing on the fully operational sTGC pad-only path based on the Pad Trigger (PT) and Trigger Processor (TP) FPGA based boards. Performance studies using 13.6TeV pp collisions are presented, demonstrating NSW’s readiness for the High Luminocity LHC (HL-LHC) era and outlining Phase II upgrade perspectives.

ATLAS New Small Wheel performance studies after first year of operation

After successfully completing Phase I upgrades during LHC Long Shutdown 2, the ATLAS detector is back in operation with several upgrades implemented. The most important and challenging upgrade is in the Muon Spectrometer, where the two inner forward muon stations have been replaced with the New Small Wheels (NSWs) system featuring two entirely new detector technologies: small strip Thin Gap Chambers (sTGC) and the resistive Micromegas (MM). After massive construction, testing and installation work in ATLAS, the two NSWs end-caps have now been in operation for about a year in the experiment, participating in the muon spectrometer tracking system and muon trigger system. A huge effort has gone into the operation of the new data acquisition system, as well as the implementation of a new processing chain within the muon software framework. Tracking is performed with full consideration of the absolute alignment of each individual detector module by the ATLAS Muon Spectrometer optical alignment system. All the deviations from the nominal geometry of all the constituent elements of each sTGC and MM module are accounted for through the modelling of the real chamber geometry reconstructed from the information of the construction databases. After an overview of the strategies adopted for the simulations and reconstruction, the studies on the performance of the NSW system in its first year of operation with LHC Run3 data will be reported.

Studying signals in particle detectors with resistive elements such as the 2D resistive strip bulk MicroMegas

Abstract As demonstrated by the ATLAS New Small Wheel community with their MicroMegas (MM) design, resistive electrodes are now used in different detector types within the Micro Pattern Gaseous Detector family to improve their robustness. The extended form of the Ramo-Shockley theorem for conductive media has been applied to a 1 MΩ/□ 2D resistive strip bulk MM to calculate the signal spreading over neighbouring channels using an 80 GeV/c muon track. For this geometry, the dynamic weighting potential was obtained numerically using a finite element solver by applying a junction condition and coordinate scaling technique to accurately represent the boundary conditions of a 10 × 10 cm2 active area. Using test beam measurements, the results of this model will be used to benchmark this microscopic modelling methodology for signal induction in resistive particle detectors.

Towards robust PICOSEC Micromegas precise timing detectors

The PICOSEC Micromegas (MM) detector is a precise timing gaseous detector consisting of a Cherenkov radiator combined with a photocathode and a MM amplifying structure. A 100-channel PICOSEC MM prototype with 10 × 10 cm2 active area equipped with a Cesium Iodide (CsI) photocathode demonstrated a time resolution below σ = 18 ps. The objective of this work is to improve the PICOSEC MM detector robustness aspects, i.e. integration of resistive MM and carbon-based photocathodes, while maintaining good time resolution. The PICOSEC MM prototypes have been tested in laboratory conditions and successfully characterised with 150 GeV/c muon beams at the CERN SPS H4 beam line. The excellent timing performance below σ = 20 ps for an individual pad obtained with the 10 × 10 cm2 area resistive PICOSEC MM of 20 MΩ/□ showed no significant time resolution degradation as a result of adding a resistive layer. A single-pad prototype equipped with a 12 nm thick Boron Carbide (B4C) photocathode presented a time resolution below σ = 35 ps, opening up new possibilities for detectors with robust photocathodes. The results made the concept more suitable for the experiments in need of robust detectors with good time resolution.

Ready for LHC Run III: the ATLAS New Small Wheel and the MicroMegas chambers performances

The two New Small Wheels (NSW) for the upgrade of the ATLAS Muon Spectrometer are now installed in the experiment and ready to collect data in LHC Run III, started in July 2022. The NSW is the largest Phase-1 upgrade project of ATLAS. Its challenging completion and readiness for data taking is a remarkable achievement of the Collaboration. The two wheels (10 meters in diameter) replace the first muon stations in the high-rapidity regions of ATLAS and are equipped with multiple layers of two new detector technologies: the small strips Thin Gap Chambers (sTGC) and the MicroMegas (MM). The latter, belong to the family of Micro Pattern Gaseous Detectors (MPGD), for the first time used in such a large scale in HEP experiments. Each detector technology will cover more than 1200 m2 of active area. The new system is designed to assure high tracking efficiency, reduction of fake trigger rates and precision measurement of muon tracks, also in view of the higher background environment foreseen for Hi-Lumi LHC. In this presentation, the motivation of the NSW upgrade and the steps from the commissioning to the data taking together with the first results using the Run III data will be presented, focusing on the MicroMegasperformances.

Validation of the New Small Wheel Micromegas sectors for the phase 1 upgrade of the muon forward spectrometer of the ATLAS experiment at CERN

The ATLAS experiment is currently upgrading the first muon station in the high-rapidity region with the New Small Wheels (NSW), based on large-size resistive Micromegas (MM) technology and small-strip Thin Gap Chambers (sTGC). The NSW system is going to be installed in the ATLAS underground cavern during the LHC long shutdown 2 (2021) to enter in operation for Run3 (starting in the first months of 2022). 128 Micromegas quadruplets, each composed by four measurement layers two to three square meters in size, are needed to build the two New Small Wheels, covering a total active area of about 1280 m2. The construction of all MM modules, carried out in France, Germany, Italy, Russia and Greece, is completed. Their mechanical integration into sectors, the installation of on-detector services and electronics, for the first NSW is also completed, along with all validation and acceptance tests. The preparation of the second NSW is very well advanced. The advanced status of the project, in view of the imminent installation of the two NSW in ATLAS by the fall of 2021 will be reported. Micromegas detector construction and integration into sectors is presented, together with results obtained with cosmic rays data during the validation tests and the impressive steps of the wheel assembly completion.

Charge sensitive preamplifier design optimization for low-pressure Micro-Megas gaseous detector operations

Using a bulk Micro-Megas (MM) detector an energy measurement can be obtained collecting the total charge reaching the mesh electrode connected to a low noise charge sensitive preamplifier. When operating such a device in a low-pressure gas regime, it is necessary to modify the amplification gap geometry to reach the optimal detector gain. This implies changes in the input capacitance of the preamplifier influencing its signal to noise ratio and thus the detector energy resolution. An ad-hoc high-gain and low-noise charge preamplifier has been developed to cope with the requirements of our application field. In this short report, we present the development activities focused to the study of a configurable charge amplifier to be connected to a MM detector having different mesh capacitances.

Cosmic results with the final Micromegas sectors for the ATLAS Muon upgrade

With the upgraded beam luminosity in LHC Run 3, the detector technology for the innermost end-cap muon station (small wheel) of the ATLAS detector needs to be upgraded. The new technology should be able to meet the demands of spatial resolution, high efficiency as well as fast response of the present system at the expected higher background rate, up to 20 kHz/cm2. The detectors which perform precision tracking and triggering in the New Small Wheel (NSW) are Micromegas (MM) and small-strip Thin Gas Chamber (sTGC) respectively. The detectors are also complementary to each other. The Micromegas quadruplets are delivered to CERN from the different construction sites. Two Micromegas quadruplets are integrated to build a double wedge. After the electronic integration, the double wedges are tested with cosmic muons at the cosmic stand at CERN. The final high voltage configuration is verified and various parameters like the efficiency, cluster size, strip multiplicity per readout layer are measured. The double wedge of the Micromegas sector is qualified for the final integration with the sTGC wedges before mounting on the NSW. The procedure and the cosmic test results of the final validation of Micromegas double wedges is presented.

The New Small Wheel High Voltage Infrastructure

The ATLAS Muon Spectrometer is subjected to a series of upgrades in order to face the High Luminosity era of Phase-II. One of the main projects is the New Small Wheel (NSW), which has replaced the existing Small Wheel (SW), and is a perfect complement to the ATLAS Muon Spectrometer (MS) in the Endcap regions. The NSW is the combination of two prototype detector technologies, the small Thin Gap Chambers (sTGC) and the resistive Micromegas (MM). In order to operate smoothly the two technologies, a dedicated hardware infrastructure has been installed and modified accordingly based on the needs of each muon sub-system. In order to control and monitor the hardware for both technologies a Detector Control System (DCS) has been developed, following the architecture of the legacy Muon sub-systems. Aim of this work is the presentation of the development and implementation of these HV DCS systems under the Point 1 schema.

The ATLAS ‘New Small Wheel’ Muon detector stations recently commissioned for LHC Run3

After nearly a decade of intense effort, the two New Small Wheels (NSW) for the upgrade of the ATLAS Muon spectrometer is now installed in the experiment and ready for final commissioning and to collect data in LHC Run3, starting March 2022. The NSW is the largest phase-1 upgrade project of ATLAS. It is challenging completion and readiness for data taking is a remarkable achievement of the collaboration. The two wheels (10 meters in diameter) replace the first Muon stations in the high-rapidity regions of ATLAS and are equipped with multiple layers of two completely new detector technologies: the small strips Thin Gap Chambers (sTGC) and the Micromegas (MM). The latter belongs to the family of Micro Pattern Gaseous Detectors (MPGD, for the first time used in such a large scale in HEP experiment). Each detector will cover more than 1200 m2 of the active area. The new system is required to maintain the present detector’s efficiency and momentum resolution level in the expected higher background level, given the ongoing LHC luminosity upgrades. In addition, it is necessary to keep an acceptable Muon trigger rate with the same Muon momentum threshold.11Copyright 2022 CERN for the benefit of the ATLAS muon collaboration. Reproduction of this article or parts of it is allowed as specified in the CC-BY-4.0 license.

Characterization of a low-pressure Micro-Megas-like gaseous detector with low energy x-ray sources

Within the family of the Micro Strip Gas Detectors (MSGD), the intrinsic characteristics of the bulk Micro-Megas (MM) device represent the most promising features for the construction of a new instrument to be operated as a TPC gas chamber in a low-pressure regime. In this study, we present the main properties of a low-pressure bulk MM detector in which the amplification gap was slightly increased to improve the gas gain. Two configurations have been deeply studied: the first one with a gap of 128μm and a second one with a 192μm gap, both filled and operated with a gas mixture (Ar-CO2) at pressures below 100 mbar. The dependence of the gain and the energy resolution on the amplification field, gas pressure and drift field have been evaluated. The reliability of the measured performance, combined with the simple and robust structure of the detector even with an increased length of amplification gap, make it an attractive choice for applications where the track length of low energy particles is detected by using a low-pressure filling gas.

Micromegas sectors for the ATLAS muon upgrade, towards the installation of the New Small Wheel in 2021

The ATLAS experiment is currently upgrading the first muon station in the high-rapidity region with the construction of new detector structures, named New Small Wheels (NSW), based on large-size multi-gap resistive strip Micromegas (MM) technology and small-strip Thin Gap Chambers (sTGC). The NSW is being installed in the ATLAS underground cavern during the on-going LHC long shutdown 2 to enter operation for run 3. 128 Micromegas quadruplets, each of which provides four measurements of a particle track, are needed to build the two New Small Wheels, covering a total active area of about 1280 m2. The construction of all MM modules, carried out in France, Germany, Italy, Russia and Greece, is completed. Their mechanical integration into sectors, and the installation of on-detector services and electronics for the first NSW is also completed, along with all validation and acceptance tests. The preparation of the second NSW is well advanced. The advanced status of the project, in view of the imminent installation of the two NSW in ATLAS by the 2021 is reported. The integration workflow of Micromegas detectors into sectors is described with focus on cosmic rays results of the final validation tests.

Construction and operation of large scale Micromegas detectors for the ATLAS Muon upgrade

After the forthcoming upgrade of the LHC accelerator at CERN, its luminosity will increase up to 7.5 × 1034 cm−2s−1. That will raise the readout rates and the background data to unmanageable levels for the existing ATLAS muon spectrometer. The ATLAS collaboration has proposed to replace the present small wheel muon detector with the New Small Wheel (NSW) to surpass those limitations. The new wheels consist of Micromegas (MM) and small-strip Thin Gap Chambers (sTGC). The first technology aims for precision tracking, and the last one for trigger purposes. Each wheel will be equipped with eight small and eight large sectors, while each sector will have a double MM wedge surrounded by sTGC wedges. The MM detectors for the NSW will be the largest developed Micro Pattern Gaseous Detector (MPGD) as they will cover an area up to 1280 m2. During detectors’ manufacture have been used various custom materials (PCBs, mesh) and innovative construction techniques. This paper describes the MM drift panels production at Aristotle University of Thessaloniki laboratory. Then will be presented resolution results of the MM detectors with cosmic-ray tests at CERN facilities.

The Micromegas Surface Commissioning For the ATLAS New Small Wheel

In order to cope with the required precision tracking and trigger capabilities from Run III onward in the ATLAS experiment, the innermost layer of the Muon Spectrometer end-cap (Small Wheels) will be upgraded. Each of the two New Small Wheels (NSW) will be equipped with eight layers of MicroMegas (MM) detectors and eight layers of small-strip Thin Gap Chambers (sTGC), both arranged in two quadruplets. MM detectors of large size (up to 3m2) will be employed for the first time in HEP experiments.Four different types of MM quadruplet modules (SM1, SM2, LM1, LM2), built by different Institutes, compose the NSW. The modules are then sent to CERN, integrated into double wedges (DW), tested and sent for commissioning on the wheel itself. At the commissioning stage the MM double wedges along with the sTGC wedges are assembled together into sectors which are then installed and tested on the wheel. Each wheel comprises 8 small (made of SM1 and SM2 modules) and 8 large (made of LM1 and LM2 modules) sectors, in order to provide full coverage of the end caps.The first of the two wheels (NSW-A) has been fully commissioned, installed in ATLAS and the first tests are currently ongoing. The second wheel (NSW-C) is currently under commissioning and is expected to be ready by October this year.

Implementation of the DCS System for the validation of MM HV Boards and the DCS System of the new BIS78 Chambers for the upgrade of muon system of the ATLAS Experiment

The ATLAS Muon Spectrometer is going through upgrades on the Phase I in order to achieve higher rates for the upcoming LHC runs. The two main projects of this Phase I upgrade are the New Small Wheels (NSW), which are expected to complement the ATLAS muon spectrometer in the end-cap regions and a smaller size project, known as BIS78 (Barrel Inner Small sectors).The NSW is expected to replace the Small Wheel (SW) and it will be installed in the ATLAS underground cavern during the summer by the end of the LHC Long Shutdown 2. This new system will be consisted by two prototype detectors, the sTGC (small Thin Gas Chambers) and the resistive Micromegas (MM).In order to cope with higher LHC luminosities, the installation of NSW will help the reduction of the trigger rate in the forward region. With half of the rate in the barrel-endcap transition region reduced by the existing TGCs, the other half of the fake trigger rate in transition region will be reduced by the new BIS78 stations. The BIS78 subproject foresees the replacement of the existing Monitored Drift Tubes (MDTs), used for the precise position measurement in this area, with muon stations formed by integrated smaller diameter tubes (sMDT) and a new generation of RPCs, capable of withstanding the higher rates and provide a robust standalone muon confirmation. The existing BIS7 and BIS8 MDT Chambers will be replaced by 16 new muon stations of one small (sMDT) chamber and two RPC triplets, and it will be the pilot project for the Phase II BI Upgrade.This work is divided into two parts. First will be presented the development and the implementation of a Detector Control System (DCS) for the HV system for the MM detectors of NSW and specifically the validation of a new type of HV Boards (A7038AP). Second, the development of the DCS for the monitoring and operation of the new sMDT chambers of the MDT Sub-System will be presented.

An overview of the ATLAS New Small Wheel Micromegas construction project at Aristotle University

The upcoming luminosity upgrade of the LHC will impose new requirements for the detector installations. To perform under these conditions the Micromegas (MM) technology was selected to be adopted in the New Small Wheel (NSW) upgrade, dedicated to precision tracking. A large surface of the forward regions of the Muon Spectrometer will be equipped with 8 layers of MM modules forming a total active area of 1200 m2. The NSW is planned to be installed in the forward region of [Formula: see text] of ATLAS. This new system will have to operate in a high background radiation region, while reconstructing muon tracks as well as furnishing information for the Level-1 trigger. The project requires fully efficient MM chambers with spatial resolution down to 100 [Formula: see text]m, a rate capability up to about 15 kHz/cm2 and operation in a moderate (highly inhomogeneous) magnetic field up to [Formula: see text][Formula: see text]T. The required tracking is linked to the intrinsic spatial resolution in combination with the demanding mechanical accuracy. An overview of the design, construction and QA/QC procedures followed at the Aristotle University of Thessaloniki for the Micromegas LM2 Drift panels production will be presented.

New Small Wheels for the ATLAS Muon Spectrometer

The ATLAS collaboration at Large Hadron Collider (LHC) has chosen the Large size multi-gap resistive strips Micromegas (MM) technology along with the small-strip Thin Gap Chambers (sTGC) for the High Luminosity (HL) upgrade of the first muon station in the high-rapidity region, the so called New Small Wheel (NSW) project. The NSW is expected to be installed in the ATLAS underground cavern in the current long shutdown. After the R&D, design and prototyping phase, series production MM and sTGC chambers are being constructed. At CERN, the final validation and integration of the modules in sectors composing the wheel is well advanced. The achievement of the requirements for these detectors revealed to be even more challenging than expected, when scaling from the small prototypes to the large dimensions. In this document the main challenges of the project, the adopted solutions and performance results are presented.

Small-strip thin gap chambers for the muon spectrometer upgrade of the ATLAS experiment

The instantaneous luminosity of the Large Hadron Collider at CERN will be increased by about a factor of five with respect to the design value after the extensive upgrade program over the coming decade. In order to cope with the increasing luminosity, the ATLAS experiment is being upgraded as well. The largest phase-1 upgrade project for the ATLAS Muon System is the replacement of the present first station in the forward regions with the New Small Wheels (NSWs) during the long-LHC shutdown in 2019-2021. The NSWs are based on two detector technologies: Micromegas (MM) and small-strip TGC (sTGC), the later arranged in two quadruplets, each consisting of 8 layers. To retain the good precision tracking and trigger capabilities in the high background environment of the high luminosity LHC, each sTGC plane must achieve a spatial resolution better than 100 μm. It will allow to reconstruct tracks with an angular resolution of approximately 1 mrad. The sTGC design, performance, construction and integration status are discussed, along with results from tests of the chambers with nearly final electronics with beams, cosmic rays and high-intensity radiation sources.

The Micromegas chambers for the ATLAS New Small Wheel upgrade

The ATLAS collaboration at the LHC has chosen the resistive Micromegas (MM) technology, along with the small-strip Thin Gap Chambers (sTGC), for the high luminosity upgrade of the first muon station in the high-rapidity region, the so called New Small Wheel (NSW) project. After the R&D, design and prototyping phase, the first series production Micromegas quadruplets are being constructed at the involved construction sites in France, Germany, Italy, Russia and Greece. At CERN, the final validation and the integration of the modules in Sectors are in progress. These are big steps forward for the installation of the NSW foreseen for the LHC long shutdown in 2019 and 2020. The construction of the four types of large size quadruplets, all having trapezoidal shapes with surface areas between 2 and 3 m2, will be reviewed. Achieving the requirements for these detectors has proven to be even more challenging than expected, when scaling from the small prototypes to large dimensions. We will describe the encountered problems, to a large extent common to other micro-pattern gaseous detectors, and the adopted solutions. Final quality assessment of the High-Voltage stability of the modules, with and without irradiation, will be presented together with the most relevant steps and results.