ATLAS Barrel Research Articles

Production and test of BI-RPC detectors for ATLAS Phase-2 upgrade

The current Resistive Plate Chamber (RPC) system is undergoing a major upgrade (ATL (2017)), consisting in the installation of approximately 1000 RPC detector units in the innermost barrel layer of the ATLAS Muon Spectrometer. The goal of the project is to increase the detector coverage, currently limited to approximately 80%, and improve the trigger robustness and efficiency. The production of the gas volumes takes place in Italy, in Germany and China, while the readout panels in Cosenza (Italy) and Hefei (China). The Italian collaboration is taking care of the construction and test of the chambers located in the large sectors of the ATLAS barrel (BIL). Here we present the state of the art of the production, certification and logistics related to all the components produced at the Italian sites, as well as the assembly line and characterization of the BIL chambers at CERN with cosmic rays. The certification results of the components produced are analyzed and discussed.

Status of the Level-0 ATLAS barrel muon trigger for High-Luminosity LHC

The Muon Spectrometer of the ATLAS detector will be substantially modified during the Phase-II Upgrade to cope with the higher particle rates and radiation levels of the High-Luminosity LHC. The entire trigger and readout electronics of the Resistive Plates Chambers will be replaced. The Resistive Plate Chambers’ hit data will be collected by on-detector Data Transmitter and Collector boards and will be sent off-detector to the Sector Logic boards, which will perform the Level-0 barrel muon trigger algorithm and the readout logic. This contribution presents the design of the Phase-II barrel muon trigger and data acquisition system and the development of the barrel Sector Logic board firmware and its challenges.

Studies of the gas volume current density in the ATLAS Resistive Plate Chamber detector during the 2018 data-taking at the LHC

The ATLAS Resistive Plate Chamber (RPC) detector is a tracking detector, used to primarily trigger muons in the ATLAS barrel region (which corresponds to a pseudorapidity range of |η|<1.05) at the 40 MHz collision rate, and to provide η and ϕ coordinates. The RPC system consists of about 3700 gas volumes covering a sensitive surface of about 4000 m2. It is arranged in three concentric doublet layers at radius 7 m, 8 m and 10 m, and operating in an approximately 0.5–1 T toroidal magnetic field. RPCs provide up to 6 space points along the muon track with a space-time resolution of about 1 cm2 × 1 ns. This document studies systematically the gas volume current as a function of the electric field applied across the gas volume and of temperature both with and without the Large Hadron Collider (LHC) beam induced background and up to an instantaneous luminosity Linst = 2×1034 cm−2 s−1 (twice larger than the design LHC luminosity). These measurements have been used to study the RPC working conditions and to extrapolate the detector response to the High-Luminosity LHC regime with Linst = 7.5×1034 cm−2 s−1.

The BIS78 Resistive Plate Chambers upgrade of the ATLAS Muon Spectrometer for the LHC Run-3

Resistive Plate Chambers (RPCs) are used in the ATLAS experiment for the muon trigger and two coordinate measurements in the central region. In preparation for the coming years of LHC running at higher luminosity, besides the New Small Wheel project which is expected to complement the ATLAS muon spectrometer in the end-cap regions, a smaller size project, known as BIS78 (from Barrel Inner Small sectors), is being developed with a foreseen installation during the LHC Long Shutdown 2 (2019–2020). The BIS78 project will reinforce the fake muon rejection and the selectivity of the muon trigger in the transition region between the ATLAS barrel and end-caps by adding 32 RPC triplets on the edges of the Inner Barrel even sectors (BIS7 and BIS8) as this region is characterized by high rate due to secondary charged tracks generated by beam halo protons and a lack of detector instrumentation. Each triplet will be a station composed by three independent RPC detectors. Due to the narrow available space, the project foresees to replace 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. These new RPCs are based on novel design of the gas volume with a thinner gas gap, thinner resistive electrodes, a lower operating voltage and new high gain front-end electronics with respect to the legacy ATLAS RPCs. Besides the use in Run-3 and onwards, this project is also of particular relevance as a pilot test for the High Luminosity LHC upgrade when an additional full layer of new RPC triplets is expected to complement the full barrel region in the innermost plane. The core of the project is presented, together with a description of the production and the test results. Details on the detector infrastructure and services along with a roadmap towards the final installation and commissioning during the Long Shutdown 2 (2019–2020) are also discussed.

Test up to 80 kA of an Al-Stabilized NbTi Cable With the Upgraded Saclay Superconducting Transformer

An ATLAS Barrel Toroid conductor was tested in the Saclay High Current Test Facility. The conductor is a Nb-Ti Rutherford cable imbedded in a high purity aluminum stabilizer. The conductor's width was reduced from 57 mm to 30 mm in order to be able to use an existing sample holder. We tried to measure the critical current in background fields of up to 3 T. The field was produced by a 0.8 m long superconducting dipole magnet. The test station was equipped with a superconducting transformer transferring maximum primary and secondary currents of respectively 174 A and 80 kA. The secondary current was measured with flux coils and with a superconducting Direct Control Current Transducer (DCCT), a modified version of the “Macc+” 600 A commercial DCCT from Hitec, which was operated at currents of up to 57 kA. This paper reports on the performance of the test station, on the results of the quench current measurements performed on the stabilized ATLAS conductor and on the difficulties to measure the critical current of an aluminum stabilizer conductor.

The Superconducting Toroid for the New International AXion Observatory (IAXO)

IAXO, the new International AXion Observatory, will feature the most ambitious detector for solar axions to date. Axions are hypothetical particles which were postulated to solve one of the puzzles arising in the standard model of particle physics, namely the strong CP (Charge conjugation and Parity) problem. This detector aims at achieving a sensitivity to the coupling between axions and photons of one order of magnitude beyond the limits of the current detector, the CERN Axion Solar Telescope (CAST). The IAXO detector relies on a high-magnetic field distributed over a very large volume to convert solar axions to detectable X-ray photons. Inspired by the ATLAS barrel and end-cap toroids, a large superconducting toroid is being designed. The toroid comprises eight, one meter wide and twenty one meters long racetrack coils. The assembled toroid is sized 5.2 m in diameter and 25 m in length and its mass is about 250 tons. The useful field in the bores is 2.5 T while the peak magnetic field in the windings is 5.4 T. At the operational current of 12 kA the stored energy is 500 MJ. The racetrack type of coils are wound with a reinforced Aluminum stabilized NbTi/Cu cable and are conduction cooled. The coils optimization is shortly described as well as new concepts for cryostat, cold mass, supporting structure and the sun tracking system. Materials selection and sizing, conductor, thermal loads, the cryogenics system and the electrical system are described. Lastly, quench simulations are reported to demonstrate the system's safe quench protection scheme.

Conceptual Design of a New Large Superconducting Toroid for IAXO, the New International AXion Observatory

The International AXion Observatory (IAXO) will incorporate a new generation detector for axions, a hypothetical particle, which was postulated to solve one of the puzzles arising in the standard model of particle physics, namely the strong CP problem. The new IAXO experiment is aiming at achieving a sensitivity to the coupling between axions and photons of one order of magnitude beyond the limits of the current state-of-the-art detector, represented by the CERN Axion Solar Telescope (CAST). The IAXO detector relies on a high-magnetic field distributed over a very large volume to convert solar axions into x-ray photons. Utilizing the designs of the ATLAS barrel and end-cap toroids, a large superconducting toroidal magnet is currently being designed at CERN to provide the required magnetic field. The new toroid will be built up from eight, one meter wide and 20 m long, racetrack coils. The toroid is sized about 4 m in diameter and 22 m in length. It is designed to realize a peak magnetic field of 5.4 T with a stored energy of 500 MJ. The magnetic field optimization process to arrive at maximum detector yield is described. In addition, force and stress calculations are performed to select materials and determine their structure and sizing. Conductor dimensionality, quench protection and the cryogenic design are dealt with as well.

Study of energy response and resolution of the ATLAS barrel calorimeter to hadrons of energies from 20 to 350 GeV

A fully instrumented slice of the ATLAS detector was exposed to test beams from the SPS (Super Proton Synchrotron) at CERN in 2004. In this paper, the results of the measurements of the response of the barrel calorimeter to hadrons with energies in the range 20–350GeV and beam impact points and angles corresponding to pseudo-rapidity values in the range 0.2–0.65 are reported. The results are compared to the predictions of a simulation program using the Geant 4 toolkit.

Measurement of the response of the ATLAS liquid argon barrel calorimeter to electrons at the 2004 combined test-beam

During summer and fall 2004, the response of a full slice of the ATLAS barrel detector to different particles was studied in controlled beam. One module of the ATLAS liquid argon barrel calorimeter—identical to the production modules and read out by the final front-end and back-end electronics—was used for electromagnetic calorimetry. This paper presents and discusses the electron performance of the LAr barrel calorimeter, including linearity, uniformity, and resolution with different amounts of material upstream the calorimeter and energies ranging from 1 to 250 GeV.

Comparison of data with Monte Carlo simulations at the ATLAS barrel combined testbeam 2004

The scheme adopted as baseline by ATLAS for the calibration of hadrons depends strongly on the quality of the description of the data by simulations. In 2004, the calorimeters of the ATLAS barrel region have been exposed to a testbeam in order to evaluate the energy response of pions for the energies ranging from 1 to 350 GeV. For the energy region from 3 to 9 GeV a data analysis with the full systematic uncertainty is available. The data has been compared extensively to GEANT4 simulations. Several combinations of physical models—the so called "physics lists"—are provided by the GEANT4 collaboration and have been evaluated. The best overall description of data is achieved with the physics list QGSP_BERT which describes the energy response of pions within a few percent. QGSP_BERT has been adopted by ATLAS for the simulation of the first data.

Upgrading the ATLAS barrel tracker for the super-LHC

It has been proposed to increase the luminosity of the large hadron collider (LHC) at CERN by an order of magnitude, with the upgraded machine dubbed super-LHC. The ATLAS experiment will require a new tracker for this high-luminosity operation due to radiation damage and event density. In order to cope with the order of magnitude increase in pile-up backgrounds at the higher luminosity, an all-silicon tracker is being designed. The new strip detector will use significantly shorter strips than the current silicon tracker in order to minimize the occupancy. As the increased luminosity will mean a corresponding increase in radiation dose, a new generation of extremely radiation-hard silicon detectors is required. An R&D program is underway to develop silicon sensors with sufficient radiation hardness. New front-end electronics and readout systems are being designed to cope with the higher data rates. The challenges facing the sensors and the cooling and mechanical support will be discussed. A possible tracker layout will be described.

ATLAS tile calorimeter cesium calibration controland analysis software

An online control system to calibrate and monitor ATLAS Barrel hadroniccalorimeter (TileCal) with a movable radioactive source, driven by liquid flow, is described.To read out and control the system an online software has been developed, using ATLASTDAQ components like DVS (Diagnostic and Verification System) to verify the hardware beforerunning, IS (Information Server) for data and status exchange between networked computers,and other components like DDC (DCS to DAQ Connection), to connect to PVSS-based slowcontrol systems of Tile Calorimeter, high voltage and low voltage. A system of scripting facilities,based on Python language, is used to handle all the calibration and monitoring processes fromhardware perspective to final data storage, including various abnormal situations. A QT basedgraphical user interface to display the status of the calibration system during the cesium sourcescan is described. The software for analysis of the detector response, using online data, isdiscussed. Performance of the system and first experience from the ATLAS pit are presented.

Hot Spot in ATLAS Barrel Toroid Quenches

The ATLAS Barrel Toroid, the largest toroid ever built with 1.1 GJ stored energy, has been successfully tested after installation in the underground cavern in fall 2006. The eight coils of the Barrel Toroid were tested individually before and showed fully acceptable performances. We observed only one training quench during an individual coil test (at 30 A below the maximum test current) and no training during the test of the fully assembled toroid. At currents up to the nominal value of 20.5 kA, the toroid has been quenched inducing normal zones by means of heaters or by stopping the helium flow in the current leads. The quench safety system worked perfectly. Given the safe peak temperatures measured in the cold mass following various quenches, it is concluded that the Barrel Toroid can be operated safely. In this paper, the hot spot of the toroid is presented in detail: the measurement data are compared to various theoretical models.

Cryogenic Characteristics of the ATLAS Barrel Toroid Superconducting Magnet

ATLAS, one of the experiments of the LHC accelerator under commissioning at CERN, is equipped with a large superconducting magnet the Barrel Toroid (BT) that has been tested at nominal current (20500 A). The BT is composed of eight race-track superconducting coils (each one weights about 45 tons) forming the biggest air core toroidal magnet ever built. By means of a large throughput centrifugal pump, a forced flow (about 10 liter/second at 4.5 K) provides the indirect cooling of the coils in parallel. The paper describes the results of the measurements carried out on the complete cryogenic system assembled in the ATLAS cavern situated 100 m below the ground level. The measurements include, among other ones, the static heat loads, i.e., with no or constant current in the magnet, and the dynamic ones, since additional heat losses are produced, during the current ramp-up or slow dump, by eddy currents induced on the coil casing.

Mechanical Commissioning of the ATLAS Barrel Toroid Magnet

ATLAS is a general-purpose detector designed to run at the highest luminosity at the CERN Large Hadron Collider. Its features include the 4 T Barrel Toroid magnet, the largest superconducting magnet (25 m long, 20 m diameter) that provides the magnetic field for the ATLAS muon spectrometer. The coils integrated at CERN, were tested individually at maximum current of 22 kA in 2005. Following the mechanical assembly of the Barrel Toroid in the ATLAS underground cavern, the test of the full Barrel Toroid was performed in October 2006. Further tests are foreseen at the end 2007 when the system will include the two End Cap Toroids (ECT). The paper gives an overview of the good mechanical test results achieved in comparison with model predictions and the experience gained in the mechanical behavior of the ATLAS Toroidal coils is discussed.

Recent results from 2004 ATLAS calorimeter combined test beam

During a combined test beam in summer 2004 a slice of the ATLAS barrel detector (including all detector sub systems from the inner tracker, the calorimetry to the muon system) was exposed to particle beams (electrons, pions, photons and muons) with different energies (1 GeV to 350 GeV). The aim was to study the combined performance of the different detector sub systems in ATLAS-like conditions. We will present the electronics calibration scheme of the electromagnetic calorimeter and its implementation. The following studies on the combined test beam data have been performed and will be presented: performance of the electromagnetic calorimetry down to very low energies (E < 10 GeV). These measurements have been compared to Monte Carlo simulations showing a good agreement to the data. Results for electrons will be presented and compared to MC simulation.

ATLAS Liquid Argon Barrel Calorimeter Performance in the 2004 Combined Test-Beam

During the combined test-beam in summer 2004 a slice of the ATLAS barrel detector - including all detector sub systems from the inner tracker and the calorimetry, to the muon system - was exposed to particle beams (electrons, pions, photons, muons) with different energies (1 GeV to 350 GeV). The aim was to study the combined performance of the different detector sub systems in ATLAS-like conditions. We present performance results from the electromagnetic calorimetry, including uniformity, resolution, and linearity using two different calibration approaches.

ATLAS liquid argon barrel calorimeter performance in test-beams

During the combined test-beam in summer 2004 a slice of the ATLAS barrel detector—including all detector sub-systems from the inner tracker, the calorimetry to the muon system—was exposed to particle beams (electrons, pions, photons, muons) with different energies (1–350 GeV). The aim was to study the combined performance of the different detector sub-systems in ATLAS-like conditions. We will present studies with different amounts of material in front of the calorimeter, representing various regions in the ATLAS detector, performance results from the electromagnetic calorimetry, including energy reconstruction, uniformity, resolution and linearity. The performance in the combined ATLAS like set-up will be compared to the one obtained in stand-alone test-beams.

The control on the deformation of the ATLAS barrel toroid warm structure

The ATLAS barrel toroid warm structure supports the barrel toroid and the muon detectors. The warm structure is about 26 meters long with an outer diameter of 20 meters. In order to ensure the physics performance of the muon detectors, the deformation of the warm structure is minimised during the design phase. The barrel toroid assembly has been carried out in the cavern of the ATLAS experiment since end of 2004. In September 2005, the warm structure has been completely released. The release has been followed-up in real time using optical alignment sensors. Good agreement has been found within 1 mm, between the alignment system measurement, the geometer survey and the predicted values according to the finite element analyses results.

ATLAS electromagnetic barrel calorimeter performance in recent testbeams

During the combined testbeam in summer 2004 a slice of the ATLAS barrel detector—including all detector sub systems from the inner tracker, the calorimetry to the muon system—was exposed to particle beams (electrons, pions, photons, muons) with different energies (1–350 GeV). The aim was to study the combined performance of the different detector sub systems in ATLAS-like conditions. We will present studies with different amounts of material in front of the calorimeter, representing various regions in the ATLAS detector, performance results from the electromagnetic calorimetry, including uniformity, resolution, and linearity as well as a discussion of the calibration scheme. The performance in the combined ATLAS-like set-up will be compared to the one obtained in stand-alone testbeams.