Micromegas Research Articles

Electronics performance of the ATLAS New Small Wheel Micromegas wedges at CERN

A series of upgrades are planned for the LHC accelerator to increase its instantaneous luminosity to 7.5 × 1034 cm−2s−1. The luminosity increase drastically impacts the ATLAS trigger and readout data rates. The present ATLAS small wheel muon detector will be replaced with a New Small Wheel (NSW) detector which is expected to be installed in the ATLAS underground cavern by the end of the Long Shutdown 2 of the LHC . With the final micromegas (MM) quadruplets (modules) already produced the activities concerning the integration of the modules into the final, fully equipped MM wedges, that will then be installed on the wheel structure on surface, are currently in full swing at CERN. One crucial part of the integration procedure concerns the installation, testing and validation of the on-detector electronics and readout chain for a very large system with more than 2.1 millions electronic channels in total. These include ∼4 thousands MM Front-End Boards (MMFE8), custom printed circuit boards each one housing eight 64-channel VMM Application Specific Integrated Circuits (ASICs) that interface with the ATLAS Trigger and Data Acquisition (TDAQ) system through ∼1 thousands data-driver cards (ADDC & L1DDC, respectively). The readout chain is based on optical link technology (GigaBit Transceiver links) connecting the back-end to the front-end electronics via the Front-End LInk eXchange (FELIX), a newly developed system that will serve as the next generation readout driver for ATLAS. Experience and performance results from the first large-scale electronics integration tests performed at CERN on final MM wedges, including system validation with cosmic-rays, are presented.

Mechanical modelling of the micromegas detectors for the atlas new small wheel

In order to benefit from the expected high luminosity performance provided by the Phase-I upgraded LHC at CERN, the New Small Wheel (NSW) will be installed in the ATLAS detector during the Long Shutdown 2. The ATLAS NSW will be equipped with a new technology for the detection of muons: the MicroMegas (MM) detectors. They consist of different panels made of composite materials and when charged particles traverse the drift space, the gas is ionized and electrons are liberated; the avalanche of electrons takes place in the amplification region after the mesh and they are detected by read-out strips to reconstruct the trajectory of muons produced after the collision. Very tight mechanical tolerances are given in the design phase and they must be preserved from the panel construction to the final operation in the ATLAS cavern.In this paper the construction procedure of these very precise particle detectors is described and the mechanical modelling to predict their mechanical behaviour is presented. Finally, the experimental tests done to validate the numerical models are discussed.

High voltage stability and cleaning of 2 m2 resistive strip micromegas detectors (SM2) for the upgrade of the forward muon spectrometer of the ATLAS experiment

Abstract For the upgrade of the innermost station of the forward muon spectrometer of the ATLAS experiment large Micromegas (MM) detectors of 2 and 3 m 2 with 4 active layers each are foreseen. Four types of MM chambers are produced among four sites. Each sites has to deliver 32 quadruplets or 128 active planes. The tiny 120 μ m distance between the 600 V resistive strip anodes and the ground micro-meshes for these large areas require adequate and well adapted cleaning procedures to guarantee high voltage stability. This is particularly critical for strip shaped surfaces made from resistive material where remnants from the lithographic production processes must be completely removed. The procedure foreseen a visual inspections to be carried on during cleaning and assembly procedures; a wet cleaning procedure to remove dust and possible ionic components of salts from the anode surfaces; a dry cleaning procedure to remove dust; HV tests to be done to validate the cleaning. The cleaning procedure will be illustrated for a New Small Wheel (NSW) Outer Small Module (SM2) of 2 m 2 .

Characterization of a hybrid GEM-Micromegas detector with respect to its application in a continuously read out TPC

In the context of the upgrade of the LHC during the second long shutdown the interaction rate of the ALICE experiment will be increased up to 50 kHz for Pb-Pb collisions. As a consequence, a continuous read-out of the Time Projection Chamber (TPC) will be required. To keep the space-charge distortions at a manageable size, the ion backflow of the charge amplification system has to be significantly reduced. At the same time an excellent detector performance and stability of the system has to be maintained. A solution with four Gaseous Electron Multipliers (GEMs) has been adopted as baseline solution for the upgraded chambers. As an alternative approach a hybrid GEM-Micromegas detector consisting of one Micromegas (MM) and two GEMs has been investigated. The recent results of the study of the hybrid GEM-Micromegas detector will be presented and compared to measurements with four GEM foils.

Construction and performance of the sTGC and MicroMegas chambers for ATLAS NSW upgrade

The innermost stations of the current ATLAS muon end-cap system, the Small Wheels, must be upgraded in 2019 to retain their good precision tracking and trigger capabilities in the high background environment expected with the upcoming luminosity increase of the LHC. The New Small Wheels (NSW) will employ two chamber technologies: eight layers of MicroMegas (MM) arranged in two quadruplets, sandwiched between two quadruplets of small-strip Thin Gap Chambers (sTGC) for a total of about 2400 m2 of detection planes. All quadruplets have trapezoidal shapes with surface areas between 1 and 3 m2. Both MM and sTGC systems will independently provide trigger and tracking capabilities. The readout boards are industrially produced for both technologies and an accurate quality control is needed. In order to achieve a 15% transverse momentum resolution for 1 TeV muons, in addition to an excellent intrinsic resolution (010 μm), the mechanical precision of each plane of the assembled modules must be as good as 30 μm along the precision coordinate and 80 μm perpendicular to the chamber. In 2016 the milestone to build the first module-0 prototypes for both technologies has been reached. The construction procedure of the module-0 detectors will be reviewed, along with the results of the quality control checks performed during construction. The module-0 have been measured and subjected to a thorough validation. Results obtained with high-energy particle beams, with cosmic rays and with X-rays will be presented.

A compact multi-plate fission chamber for the simultaneous measurement of 233U capture and fission cross-sections

233 U plays the essential role of fissile nucleus in the Th-U fuel cycle. A particularity of 233 U is its small neutron capture cross-section which is about one order of magnitude lower than the fission cross-section on average. Therefore, the accuracy in the measurement of the 233 U capture cross-section essentially relies on efficient capture-fission discrimination thus a combined setup of fission and γ-detectors is needed. At CERN n_TOF the Total Absorption Calorimeter (TAC) coupled with compact fission detectors is used. Previously used MicroMegas (MGAS) detectors showed significant γ-background issues above 100 eV coming from the copper mesh. A new measurement campaign of the 233 U capture cross-section and alpha ratio is planned at the CERN n_TOF facility. For this measurement, a novel cylindrical multi ionization cell chamber was developed in order to provide a compact solution for 14 active targets read out by 8 anodes. Due to the high specific activity of 233 U fast timing properties are required and achieved with the use of customized electronics and the very fast ionizing gas CF4 together with a high electric field strength. This paper describes the new fission chamber and the results of the first tests with neutrons at GELINA proving that it is suitable for the 233 U measurement.

Track distortion in the Large prototype of a Time Projection Chamber for the International Linear Collider

A Micromegas (MM) based Time Projection Chamber (TPC) can meet the ILC requirements of continuous 3-D tracking, excellent spatial resolution and efficient pattern recognition. Seven MM modules which are commissioned on the end-plate of a Large Prototype TPC (LPTPC) at DESY, have been tested with a 5 GeV electron beam, under a 1 T magnetic field. Due to the grounded peripheral frame of the MM modules, at short drift, the electric field near the detector edge remain no longer parallel to the TPC axis. This causes signal loss along the boundaries of the MM modules as well as distortion in the reconstructed track. In presence of magnetic field, the distorted electric field introduces E×B effect. A detailed numerical study has been accomplished to understand the features of this distortion. Four Micromegas modules have been simulated resembling the experimental setup. The field lines, drift line of electrons considering diffusion in gas, nature of track distortion, residuals are numerically calculated in presence and in absence of magnetic field. The E×B effect has been simulated as well. Simulated results follow the experimental observations.

Study of a Large Prototype TPC for the ILC using Micro-Pattern Gas Detectors

In the last decade, R&D for detectors for the future International Linear Collider (ILC) has been performed by the community. The International Large Detector (ILD) is one of two detector concepts at the ILC. Its tracking system consists of a Si vertex detector, forward tracking disks and a large volume Time Projection Chamber (TPC). Within the LCTPC collaboration, a Large Prototype (LP) TPC has been built as a demonstrator. Its endplate is able to house up to seven identical modules with Micro-Pattern Gas Detectors (MPGD) amplification. Recently, the LP has been equipped with resistive anode Micromegas (MM) or Gas Electron Multiplier (GEM) modules. Both the MM and GEM technologies have been studied with an electron beam up to 6 GeV in a 1 Tesla solenoid magnet. After introducing the current R&D status, recent results will be presented including field distortions, ion gating and spatial resolution as well as future plans of the LCTPC R&D.

Development and test of the DAQ system for a Micromegas prototype to be installed in the ATLAS experiment

A Micromegas (MM) quadruplet prototype with an active area of 0.5 m2 that adopts the general design foreseen for the upgrade of the innermost forward muon tracking systems (Small Wheels) of the ATLAS detector in 2018-2019, has been built at CERN and is going to be tested in the ATLAS cavern environment during the LHC RUN-II period 2015-2017.The integration of this prototype detector into the ATLAS data acquisition system using custom ATCA equipment is presented. An ATLAS compatible Read Out Driver (ROD) based on the Scalable Readout System (SRS), the Scalable Readout Unit (SRU), will be used in order to transmit the data after generating valid event fragments to the high-level Read Out System (ROS). The SRU will be synchronized with the LHC bunch crossing clock (40.08 MHz) and will receive the Level-1 trigger signals from the Central Trigger Processor (CTP) through the TTCrx receiver ASIC. The configuration of the system will be driven directly from the ATLAS Run Control System. By using the ATLAS TDAQ Software, a dedicated Micromegas segment has been implemented, in order to include the detector inside the main ATLAS DAQ partition. A full set of tests, on the hardware and software aspects, is presented.

Micromegas detectors for the muon spectrometer upgrade of the ATLAS experiment

Large area Micromegas (MM) detectors will be employed for the Muon Spectrometer upgrade of the ATLAS experiment at the LHC. A total surface of about 150m2of the forward regions of the Muon Spectrometer will be equipped with 8 layers of MM modules. Each module covers a surface area of approximately 2–3m2 for a total active area of 1200m2. Together with the small-strips Thin Gap Chambers, they will compose the two New Small Wheels, which will replace the innermost stations of the ATLAS Endcap Muon tracking system in the planned 2018/2019 shutdown. This upgrade will maintain a low pT threshold for single muons and provide excellent tracking capabilities for the HL-LHC phase. The New Small Wheel (NSW) project requires fully efficient MM chambers with spatial resolution down to 100μm, at rate capability up to about 15kHz/cm2 and operation in a moderate (highly inhomogeneous) magnetic field up to B=0.3T. The required tracking capability is provided by the intrinsic spatial resolution combined with a challenging mechanical precision. The design, recent progress in the construction and results from the substantial R& D phase (with a focus on novel technical solutions) is presented. In the R& D phase, small and medium size single layer prototypes have been built, along with, more recently, the first two MM quadruplets in a configuration very close to the final one chosen for the NSW. Several tests have been performed on these prototypes at a high-energy test-beam at CERN, to demonstrate that the achieved performances fulfil the requirements. Recent tests applying various configuration and operating conditions are presented.

Measurement and simulation of two-phase CO2 cooling in Micromegas modules for a Large Prototype of Time Projection Chamber

The readout electronics of a Micromegas (MM) module consume nearly 26 W of electric power, which causes the temperature of electronic board to increase upto 70 ̂C. Increase in temperature results in damage of electronics. Development of temperature gradient in the Time Projection Chamber (TPC) may affect precise measurement as well. Two-phase CO2 cooling has been applied to remove heat from the MM modules during two test beam experiments at DESY, Hamburg. Following the experimental procedure, a comprehensive study of the cooling technique has been accomplished for a single MM module by means of numerical simulation. This paper is focused to discuss the application of two-phase CO2 cooling to keep the temperature below 30 ̂C and stabilized within 0.2 ̂C.

Deflection Monitoring Method Using Fiber Bragg Gratings Applied to Tracking Particle Detectors

This paper proposes the use of fiber Bragg gratings (FBGs) for the deflection monitoring of a micromegas (MM) tracking particle detector to be installed at the European Organization for Nuclear Research during a major upgrade of the experiment ATLAS within 2018. MM detectors are designed to reach high spatial and time resolution, even if the design is not yet finalized. One mandatory issue for the MM detector is a precise monitoring of the deflection of the drift and read-out electrodes and/or of the panel hosting the electrodes. To this aim, FBG strain sensors are proposed and experimentally investigated as a sensing solution to monitor the strain state of the detector support panel hosting the drift and read-out electrodes. Finally, simple postprocessing analysis based on classical beam theory considering a rigid body permits calculating the panel deflection. Preliminary experimental results on first prototypes of small and large detector panels are presented and discussed.

Status and progress of the novel photon detectors based on THGEM and hybrid MPGD architectures

We are developing large size THick GEM (THGEM)-based detectors of single photons, mainly meant for Cherenkov imaging applications. The R&D programme includes the complete characterisation of the THGEM electron multipliers, the study of the aspects related to the detection of single photons and the engineering towards large size detector prototypes. Our most recent achievements include dedicated studies concerning the ion backflow to the photocathode; relevant progress in the engineering aspects, in particularly related to the production of large-size THGEMs, where the strict correlation between the local gain-value and the local thickness-value has been demonstrated and a 300×300mm2 active area detector has been successfully operated at the CERN PS T10 test beam; the introduction of a new hybrid detector architecture, offering promising performance, which is formed by a THGEM layer which acts both as photocathode and pre-amplification device, followed by a MICROMEGAS (MM) multiplication stage. We report about the general status of the R&D programme and, in detail, about the recent progress.

Performance studies of MicroMegas for the ATLAS experiment

The performance of MicroMegas (MM) has been extensively studied during several test beam campaigns with high energy particle beams at CERN up to the year 2012, and more recently (June 2013) with electron beams at DESY. Main objectives of the tests were to demonstrate that the requirements could be achieved for the upgrade of the ATLAS Muon Spectrometer, where the MicroMegas will be mounted (along with small-strip Thin Gap Chambers — sTGC) on the New Small Wheel for forward muon detection. The MM layout and operating settings have then been chosen to satisfy the ATLAS upgrade requirements and trigger timing constraints. Results for efficiencies, time resolution and spatial resolution for perpendicular and inclined tracks are presented. Moreover, in ATLAS the MM will operate in a non-uniform magnetic field up to 0.3 T. Dedicated test beam measurements have been carried out in a variable magnetic field between 0 and 1 T. The performance of MM in magnetic fields is also reported along with a comparison to simulations.

NEXT prototypes based on micromegas

The NEXT experiment searches for neutrinoless double beta decay in 136Xe in a high pressure TPC. The detector is based on electroluminescence light measured with PMT's and SiPM's. In parallel with this baseline, a R&D program based on micromegas (MMs) detectors with pixelized anode is developed as an option to detect both energy and topology of the signals. MMs are considered as a readout for TPCs in the field of rare event searches (dark matter, axions or double beta decay). They are a good option for such experiments because of their high radiopurity, robustness and good performance regarding energy resolution and pattern recognition. In the R&D line, prototypes chambers based on micromegas were constructed to study their properties at different pressures and gas mixtures and also to test microbulk micromegas in conditions where electron tracks could be fully contained. The results on the commissioning and performance of these prototypes are here presented.

Simultaneous measurement of neutron-induced capture and fission reactions at CERN

The measurement of the capture cross-section of fissile elements, of utmost importance for the design of innovative nuclear reactors and the management of nuclear waste, faces particular difficulties related to the $ \gamma$ -ray background generated in the competing fission reactions. At the CERN neutron time-of-flight facility n_TOF we have combined the Total Absorption Calorimeter (TAC) capture detector with a set of three 235U loaded MicroMegas (MGAS) fission detectors for measuring simultaneously two reactions: capture and fission. The results presented here include the determination of the three detection efficiencies involved in the process: $\ensuremath \varepsilon_{TAC}(n,f)$ , $\ensuremath \varepsilon_{TAC}(n,\gamma)$ and $\ensuremath \varepsilon_{MGAS}(n,f)$ . In the test measurement we have succeeded in measuring simultaneously with a high total efficiency the 235U capture and fission cross-sections, disentangling accurately the two types of reactions. The work presented here proves that accurate capture cross-section measurements of fissile isotopes are feasible at n_TOF.