High Luminosity LHC Upgrade Research Articles

Test Result of a Full-Scale Prototype of Beam Separation Dipole Magnet for the High-Luminosity LHC Upgrade

High Energy Accelerator Research Organization (KEK) is developing Nb-Ti based beam separation dipole (MBXF) for the high-luminosity Large Hadron Collider (HL-LHC) upgrade within the framework of CERN–KEK collaboration. This magnet produces field integral of 35 T•m in a 150 mm bore at 12 kA and 1.9 K. KEK has fabricated and tested three 2 m-long model magnets as in-house activities. After the technologies cultivated in these model magnet development was transferred from KEK to a manufacture, construction of the first full-scale prototype (MBXFP1) started in Hitachi. This paper reports test result of cold test for MBXFP1 including training, mechanical behavior, magnetic field quality and quench protection.

Radiation hard 3D silicon pixel sensors for use in the ATLAS detector at the HL-LHC

The High Luminosity LHC (HL-LHC) upgrade requires the planned Inner Tracker (ITk) of the ATLAS detector to tolerate extremely high radiation doses. Specifically, the innermost parts of the pixel system will have to withstand radiation fluences above 1 × 1016 neqcm-2. Novel 3D silicon pixel sensors offer a superior radiation tolerance compared to conventional planar pixel sensors, and are thus excellent candidates for the innermost parts of the ITk. This paper presents studies of 3D pixel sensors with pixel size 50 × 50 μm2 mounted on the RD53A prototype readout chip. Following a description of the design and fabrication steps, Test Beam results are presented for unirradiated as well as heavily irradiated sensors. For particles passing at perpendicular incidence, it is shown that average efficiencies above 96% are reached for sensors exposed to fluences of 1 × 1016 neqcm-2 when biased to 80 V.

The ATLAS ITk detector for High Luminosity LHC upgrade

The High Luminosity upgrade of the LHC (HL-LHC) will require a significant upgrade of the detectors used in the experiments, in particular for the trackers. The current ATLAS Inner Detector will be replaced with an all-silicon tracker consisting of a pixel and a strip subsystem. The design and conception are now complete and the construction of the detector is starting. The paper reviews the expected performance of the new tracker and the process of construction.

Mechanical and thermal design of the target neutral beam absorber for the High-Luminosity LHC upgrade

The High-Luminosity target neutral beam absorber (TAXN) is the radiation absorber of the neutral particle debris generated at the beam collisions carried out in the ATLAS and CMS detectors at the Large Hadron Collider (LHC). The new absorber will protect the superconducting magnets from this radiation to prevent their quenching at a design luminosity of $7.5\ifmmode\times\else\texttimes\fi{}{10}^{34}\text{ }\text{ }{\mathrm{cm}}^{\ensuremath{-}2}\text{ }{\mathrm{s}}^{\ensuremath{-}1}$. This article describes the mechanical design of the TAXN assembly and the recombination chamber together with the thermal computations performed for the water-cooling and bakeout system prepared for the engineering design review held in January, 2021. It takes into account the internal integration of the zero degree calorimeter and beam rate of neutrals luminosity detector as well as their physics case overview. In addition, it provides the beam aperture breakdown and the heat deposition expected in the absorber.

FPGA implementation of RDMA for ATLAS readout with FELIX at high luminosity LHC

The FELIX system is used as an interface between front-end electronics and commodity hardware in the server farm. FELIX is using RDMA through RoCE to transmit data from its host servers to the software readout driver using off-the-shelf networking equipment. RDMA communication is implemented using software on both end of the links. Exploring opportunities to improve data throughput as part of the high luminosity LHC upgrade, an implementation for RDMA support in the front-end FELIX FPGA is being developed. We present a proof-of-concept RDMA FPGA implementation, which will help inform the design of the FELIX platform for high luminosity LHC.

An upgraded cryogenic test stand for HL-LHC cryo-assemblies

The Fermilab horizontal test stand previously used for testing the LHC inner triplet quadrupoles has been upgraded to test cryo-assemblies for the high-luminosity LHC upgrade (HL-LHC). The test requirements of these new cryo-assemblies required additional capabilities of the test stand cryogenic system, including controlled cool-down and warm-up, helium recovery after a quench, and operation at higher pressures. Most of these upgrades were completed to support a zero-magnet test in late 2020, with the remainder of the upgrades completed to support the first pre-series cryo-assembly test in early 2022. An overview of the design and initial operating experience of the upgraded test stand cryogenic system and associated process controls system are presented in this paper.

Test system for the service hybrid of the 2S module for the CMS Phase-2 Outer Tracker upgrade

Alongside the High Luminosity LHC upgrade, the silicon tracker of the CMS detector will be replaced within the scope of the so-called Phase-2 upgrade. The new tracker will consist of an inner part (Inner Tracker with pixelated modules) and at larger radii the Outer Tracker with two different module types (PS and 2S modules). One hybrid type used on these modules is the 2S service hybrid. It provides the optical link connection of a 2S module via the Low Power Giga Bit Transceiver (lpGBT) and a Versatile Transceiver Plus module (VTRx+). It is also responsible for the module power distribution. The different responsibilities of the hybrid require a complete testing, which is performed by a dedicated custom made test card. After a hybrid has been installed on the test card, all signal connections can be tested and verified. The test system is designed to handle a high throughput during mass production. The requirements and the design for the 2S service hybrid test card are presented together with testing results of the first final 2S service hybrid prototypes.

High rate capability studies of triple-GEM detectors for the ME0 upgrade of the CMS muon spectrometer

The high-luminosity LHC (HL-LHC) upgrade is presenting new challenges for particle detector technologies. In the CMS muon system gaseous detectors, the increase in luminosity will produce a particle background ten times higher than at the LHC. To cope with the high rate environment and maintain current performance, the triple-gas electron multiplier technology is a promising candidate for high-rate capable detectors for the CMS-ME0 upgrade project in the innermost region of the forward muon spectrometer of the CMS experiment. An intense R&D and prototyping phase is currently ongoing to prove that such technology meets the stringent performance requirements of highly efficient particle detection in the harsh background environment expected in the innermost ME0 region. Here, we describe the recent rate capability studies of triple-GEM detectors operated with an Ar/CO2 (70/30) gas mixture at an effective gas gain of 2 × 104 by using a high intensity 22 keV X-ray generator. Moreover, we present a novel foil design based on double-sided segmented GEM-foils, high voltage power distribution and filtering, which the CMS muon collaboration adopted for realization of the CMS-ME0 project, and their impact on the performance of the detector in the light of new rate capability studies, with a summary of the ongoing R&D activities.

Development of a High Throughput PCIe Card for DAQ System in the ATLAS and DUNE Experiments

In the Run 3 upgrade of ATLAS experiment, the FELIX (Front-End LInk eXchange) system has been prepared as the interface between front-end electronics and common Data Acquisition (DAQ) systems. Based on a PCIe card hosted in commodity server, FELIX's flexibilty makes it has also been adopted by other experiments, such as the Single-Phase ProtoDUNE (Prototype for the Deep Underground Neutrino Experiment), sPHENIX and CBM experiments. The same PCIe based architecture is proposed for use in the ATLAS HL-LHC (High Luminosity Large Hadron Collider) upgrade and the DUNE experiment. To this end, the next generation of FELIX I/O card FLX-801 has been developed. It supports 25+ Gbps high speed fiber optical links and 16-lane Gen4 PCIe interface. There is an on-card DDR4 module to buffer event data for DUNE experiment. This paper reports on the test results for the demonstrator of this next generation card, with which main functions have been successfully evaluated.

In-pixel automatic threshold calibration for the CMS Endcap Timing Layer readout chip

We present the implementation and verification of an in-pixel automatic threshold calibration circuit for the CMS Endcap Timing Layer (ETL) in the High-Luminosity LHC upgrade. The discriminator threshold of the ETL readout chip (ETROC) needs to be calibrated regularly to mitigate the circuit baseline change. Traditional methods need a lot of communication through a slow control system hence are time-consuming. This paper describes an in-pixel automatic scheme with improvements in operating time and usability. In this scheme, a sample-accumulation circuit is used to measure the average discriminator output. A binary successive approximation and linear combination scan are applied to find the equivalent baseline. The actual calibration procedure has been first implemented in FPGA firmware and tested with the ETROC front-end prototype chip (ETROC0). The calibration circuit has been implemented with Triple Modular Redundancy (TMR) and verified with Single Event Effects (SEEs) simulation. A complete calibration process lasts 35 ms with a 40 MHz clock. In the worst case, the dynamic and static power consumption are estimated to be 300 μW and 10.4 μW, respectively. The circuit design, implemented in a 65 CMOS technology, will be integrated into ETROC2, the next iteration of the ETROC with a 16 × 16 pixel matrix.

Characterization of the CMS Endcap Timing Layer readout chip prototype with charge injection

We present the characterization of a readout Application-Specific Integrated Circuit (ASIC) for the CMS Endcap Timing Layer (ETL) of the High-Luminosity LHC upgrade with charge injection. The ASIC, named ETROC and developed in a 65 nm CMOS technology, reads out a 16× 16 pixel matrix of the Low-Gain Avalanche Detector (LGAD). The jitter contribution from ETROC is required to be below 40 ps to achieve the 50 ps overall time resolution per hit. The analog readout circuits in ETROC consist of the preamplifier and the discriminator. The preamplifier handles the LGAD charge signal with the most probable value of around 15 fC. The discriminator generates the digital pulse, which provides the Time-Of-Arrival (TOA, leading edge) and Time-Over-Threshold (TOT, pulse width) information. The prototype of ETROC (ETROC0) that implements a single channel of analog readout circuits has been evaluated with charge injection. The jitter of the analog readout circuits, measured from the discriminator's leading edge, is better than 16 ps for a charge larger than 15 fC with the sensor capacitance. The time walk resulting from different pulse heights can be corrected using the TOT measurement. The time resolution distribution has a standard deviation of 29 ps after the time-walk correction from the charge injection. At room temperature, the preamplifier's power consumption is measured to be 0.74 mW and 1.53 mW per pixel in the low- and high-power mode, respectively. The measured power consumption of the discriminator is 0.84 mW per pixel. With the ASIC alone or the LGAD sensor, The characterization performances fulfill the ETL's challenging requirements.

The Development of the Superconducting Dipoles D2 for the High Luminosity Upgrade of LHC

The recombination dipoles D2 (MBRD) for the luminosity upgrade of the Large Hadron Collider (LHC) are double aperture magnets to be placed on each side of ATLAS and CMS experiments, generating 4.5 T along a magnetic length of 7.78 m and a bore diameter of 105 mm. Its development plan foresees the construction of a short model 1.6 m long, followed by a prototype and by the series of 6 magnets. The magnet design was carried out at INFN Genova in a collaboration framework with CERN and the construction is ongoing in the industry (ASG Superconductors, Italy). The short model activities have just been accomplished after a successful power test performed at CERN, while the prototype is in its construction phase. In this contribution, the main features of the D2 magnet will be described, underlining the improvements implemented in the prototype with respect to the short model design. Then, the main results of the power test will be presented, focusing on training performance, protection scheme effectiveness and magnetic measurements.

Thermomechanical Characterisation of Copper Diamond and Benchmarking with the MultiMat Experiment

The High-Luminosity Large Hadron Collider upgrade at CERN will result in an increase in the energy stored in the circulating particle beams, making it necessary to assess the thermomechanical performance of currently used and newly developed materials for use in beam intercepting devices such as collimators and absorbers. This study describes the thermomechanical characterisation of a novel copper diamond grade selected for use in tertiary collimators of the HL-LHC. The data obtained are used to build an elastoplastic material model and implemented in numerical simulations performed to benchmark experimental data obtained from the recently completed MultiMat experiment conducted at CERN’s HiRadMat facility, where various materials shaped as slender rods were tested under particle beam impact. The analyses focus on the dynamic longitudinal and flexural response of the material, with results showing that the material model is capable of replicating the material behaviour to a satisfactory level in both thermal and structural domains, accurately matching experimental measurements in terms of temperature, frequency content, and amplitude.

Optimizing the performance of the CMS Electromagnetic Calorimeter to measure Higgs properties during Phase I and Phase II of the LHC

The CMS Electromagnetic Calorimeter (ECAL), is a high granularity lead tungstate (PbWO4) crystal calorimeter operating at the CERN LHC. The ECAL performance has been crucial in the discovery and subsequent characterization of the Higgs boson. The original ECAL design considerations, and the improvements to the energy reconstruction and energy calibration algorithms to cope with the LHC Run II are described. For the High-Luminosity LHC (HL-LHC) upgrades to ECAL are necessary. The crystals in the barrel region will be retained, defining the HL-LHC CMS barrel electromagnetic calorimeter ECAL. The readout electronics will be upgraded and operating at lower temperatures, to maintain the required performance of ECAL from 2027 onwards. The new readout electronics, the timing resolution and the electron and photon reconstruction efficiencies and energy resolution expected for HL-LHC are presented. The performance relevant to a number of key Higgs decay channels is reported.

Performance of the ATLAS Resistive Plate Chamber detector and Level-1 muon barrel trigger at √s = 13 TeV

The ATLAS experiment at the Large Hadron Collider (LHC) utilises a trigger system consisting of a first level (Level-1) trigger based on custom hardware and a higher level trigger based on computer farms. The Level-1 muon trigger system selects muon candidates with six thresholds of transverse momentum and associates them with correct LHC bunch crossings. The Level-1 muon barrel trigger uses Resistive Plate Chamber (RPC) detectors to form trigger decisions in the region of |η | < 1.05. The RPC detectors are arranged in three concentric double layers, for a total of 3700 gas volumes, with a total surface of more than 4000 square meters, operating in a toroidal magnetic field. The performance of the RPC detector system and of the Level-1 muon barrel trigger during the 2018 data-taking period is discussed in this contribution. 60.8 fb−1 out of 62.2 fb−1 of data recorded by the ATLAS detector at LHC are used. Measurements of the RPC detector response and time resolution, obtained using muon candidates produced in LHC collisions, are presented. Trigger performance and efficiency are measured with muons originating from the decay of Z bosons. Finally, studies of the RPC detector response at different high voltage and threshold settings are shown, as a preview of the expected detector performance after the High Luminosity LHC upgrade.

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.

Design and hardware evaluation of the optical-link system for the ATLAS Liquid Argon Calorimeter Phase-II Upgrade

An optical link system is being developed for the ATLAS Liquid Argon Calorimeter Phase-II upgrade. The optical link system is responsible for transmit the data of over 182 thousand detector channels from 1524 Front-End Boards (FEBs) through 26 optical fibers per FEB over 150 meters to the counting room and brings clocks, bunch crossing reset signals and slow control/monitoring signals back to the FEBs. The optical link system is based on the Low-Power GigaBit Transceivers (lpGBTs) and the Versatile optical Transceiver (VTRx+) modules, which both are being developed for the High-Luminosity LHC upgrade. An evaluation board is designed and the major functions of the optical link system are being evaluated. The design of the optical link system and the evaluation of major functions are presented in the paper.

Data-acquisition system developments for ATLAS pixel QA and QC test toward High-Luminosity LHC

In preparation for the High-luminosity LHC upgrade, the whole ATLAS inner tracker will be replaced by a new silicon detector tracker. The innermost region will be covered by silicon pixel detectors as a high density of produced particles is expected. To operate in such an environment, high-resolution sensors and a high-speed readout system are required. At the moment, the front-end readout chip prototype RD53A and a data acquisition system (the YARR system) based on a commercial FPGA board and dedicated software for quality assurance and quality control test have been developed. Due to the high density of sensor channels, the output speed from RD53A is at maximum 1.28 Gbps per line, sixteen times faster than the readout front-end chip currently used in the ATLAS pixel system. The data acquisition system needs to establish communication with 1.28 Gbps speed during the quality control tests, to validate the data acquisition path, and to optimize the procedure for data taking at high speed. From the quality control perspective this optimization allows to test large numbers of modules simultaneously exploiting the data acquisition speed reducing the time needed for the tests. Another challenging point is the novel concept of readout structure planned for the operation after installation. In High-luminosity LHC, large parts of the ATLAS data acquisition system infrastructure are going to be shared among all sub-detectors, using FELIX systems, while current ATLAS data acquisition systems are dedicated for each sub-detector. This means that all processes done in the present data acquisition system hardware need to be overhauled into software running on the new data acquisition system. To minimize the differences between the data acquisition system for operation and quality control test, we introduced the prototype FELIX system into the data acquisition path of the YARR system. In this proceeding, an established data acquisition structure for quality assurance and quality control test of the new pixel detector is introduced, and results from basic quality control tests of the pixel detector with the new readout chip are presented.

Measurement of splice resistance and normal zone propagation velocity in REBCO tapes for the Superconducting Link of HL-LHC

The Superconducting Link (SC-Link) being developed at CERN in the context of the LHC High-Luminosity upgrade (HL-LHC) will supply the current to superconducting magnets of the HL-LHC Inner Triplets and Matching Sections. The SC-Link consists of MgB2 highcurrent cables, and it includes high temperature superconducting REBCO cables making the electrical transition between the MgB2 and the current leads. Electrical protection of superconducting devices made of REBCO against unexpected quenches is challenging especially when operation is at high current density. Adequate electrical protection of REBCO cables is crucial to insure good performance of the circuit over the lifetime of the machine; protection relies on the detailed knowledge of the quench propagation velocity. In this paper we reviewed the electromagnetic properties of REBCO tapes procured for prototype work. We measured the splice resistance (Rs ) of the REBCO conductors and found a significant variation among the different batches of conductor. The normal zone propagation velocity (NZPV) was reported to be affected by the interfacial resistance which is governing the splice resistance: increasing the interfacial resistance enhances the NZPV. In order to determinate the influence of the internal resistance on the quench behaviour of the tapes, we investigated the normal zone propagation velocity of the epoxy-impregnated tapes at 77 K in self-field and 4.2 K in field up to 7 T in the FRESCA test station. We found that despite the Rs variation observed (up to factor 4), the tapes show similar NZPV at both temperatures. In addition we observed a significant field dependence of the NZPV of the tapes at 4.2 K. The results are compared to numerical simulation and discussed.

Improvement in Training Performance by Enhancing Coil Mechanical Support in the Beam Separation Dipole Model Magnet for the HL-LHC Upgrade

Nb-Ti based large-aperture beam separation dipoles (MBXFs) will be installed on both sides of two interaction points, ATLAS and CMS, for the high-luminosity LHC upgrade. The most important requirements for MBXF is a coil aperture of 150 mm and the field integral of 35 T⋅m. Nominal dipole field is 5.6 T at 12 kA and 1.9 K. KEK is in charge of developing MBXF within a framework of CERN-KEK collaboration. This study reports training performance of three 2-m long model magnets (MBXFS1–3) assembled under different mechanical support conditions. Azimuthal pre-stress both in the straight section and at coil end, and axial pre-load were controlled to counteract Lorentz force. In MBXFS2 and 3, wet-winding was also applied but solely to the coil end. Quench start locations for the model magnets are compared to validate the effectiveness of each support method.