Large Hadron Collider Upgrade Research Articles

LHC Upgrades in preparation of Run 3

The Large Hadron Collider (LHC) Long Shutdown 2 (2019–2021), following LHC Run 2, was primarily dedicated to the upgrade of the LHC Injectors but it included also a significant amount of activities aimed at consolidation of the LHC machine components, removal of known limitations and initial upgrades in view of the High-Luminosity LHC (HL-LHC) to favour the intensity ramp-up during Run 3 (2022–2025). An overview of the major modifications to the accelerator and its systems is followed by a summary of the results of the superconducting magnet training campaign to increase the LHC operation energy beyond the maximum value of 6.5 TeV reached during Run 2. The LHC configuration and the scenarios for proton and ion operation for Run 3 are presented considering the expected performance of the upgraded LHC Injectors and the proton beam intensity limitations resulting from the heat load on the cryogenic system due to beam-induced electron cloud and impedance.

High intensity beam dynamics assessment and challenges for HL-LHC

The High Luminosity (HL-LHC) project aims to increase the integrated luminosity of CERN's Large Hadron Collider (LHC) by an order of magnitude compared to its initial design. This requires a large increase in bunch intensity and beam brightness compared to the first three LHC runs, and hence poses serious collective-effects challenges, related in particular to electron cloud, instabilities from beam-coupling impedance, and beam-beam effects. Here, we present the associated constraints and the mitigation measures proposed to achieve the baseline performance of the upgraded LHC machine. We also discuss the interplay of these mitigation measures with other aspects of the accelerator, such as optics, physical and dynamic apertures, the collimation system, and crab cavities. Additional potential sources of intensity limitations are also briefly discussed.

Development of the Beam Conditions Monitoring Prime system for beam abort and luminosity monitoring in ATLAS based on a segmented polycrystalline CVD diamond system and dedicated front-end ASIC

The High Luminosity upgrade of Large Hadron Collider (HL-LHC) will increase the LHC luminosity and with it the density of particles on the detector by an order of magnitude. For protecting the inner silicon detectors of the ATLAS experiment and for monitoring the delivered luminosity, a radiation hard beam monitor was developed based on polycrystalline Chemical Vapor Deposition (pCVD) diamond detectors and a new dedicated rad-hard front-end ASIC. Due to the large range of particle flux through the detector, flexibility is very important. To satisfy the requirements imposed by the HL-LHC, our solution is based on segmenting diamond sensors into devices of varying size and reading them out with new multichannel readout ASICs divided into two independent parts — each of them serving one of the tasks of the system. This paper describes the system design including detectors, electronics, mechanics and services and presents preliminary results from the most recent detectors fabricated, using our prototype ASIC with data from beam tests at CERN.

Radiation protection challenges for the Large Hadron Collider upgrade.

In the context of the so-called Long Shutdown 3 (2026-2028), the Large Hadron Collider will be upgraded to the High-Luminosity Large Hadron Collider, allowing for approximately five more instantaneous collisions. The upgrade, maintenance and decommissioning of equipment will be mainly performed in the experimental insertions of Points 1 and 5, requiring to perform multiple interventions in high-residual radiation environment. This poses complex radiological challenges that the CERN Radiation Protection group is called to address. Radiation protection studies are performed to plan and optimise (ALARA) these future interventions using the advanced Monte Carlo techniques and tools such as FLUKA, ActiWiz, SESAME and the FCC method. This paper aims to provide an overview of the studies conducted to estimate the residual radiation field in the experimental insertions, the activation levels in terms of multiple of the Swiss clearance limits/specific activity and to provide preliminary considerations on the upgrade/decommissioning of key equipment.

Development of a System for Beam Abort and Luminosity Determination at the HL-LHC based on polycrystalline CVD diamond

The high luminosity upgrade of Large Hadron Collider will increase its luminosity by an order of magnitude increasing with it the density of particles on the detector. For protecting the inner detectors of experiments and for monitoring the delivered luminosity, a radiation hard beam monitor is being developed. Text describes the proposed system’s principles of operation and its design. It details on the poly-crystalline chemical vapor deposition diamonds as sensor material, a dedicated radiation hard ASIC, as well as on electronics and data processing. The latter finally offers beam abort and luminosity measurement functionalities of the system.

Unsupervised Learning and Online Anomaly Detection

The Large Hadron Collider (LHC) demands a huge amount of computing resources to deal with petabytes of data generated from High Energy Physics (HEP) experiments and user logs, which report user activity within the supporting Worldwide LHC Computing Grid (WLCG). An outburst of data and information is expected due to the scheduled LHC upgrade, viz., the workload of the WLCG should increase by 10 times in the near future. Autonomous system maintenance by means of log mining and machine learning algorithms is of utmost importance to keep the computing grid functional. The aim is to detect software faults, bugs, threats, and infrastructural problems. This paper describes a general-purpose solution to anomaly detection in computer grids using unstructured, textual, and unsupervised data. The solution consists in recognizing periods of anomalous activity based on content and information extracted from user log events. This study has particularly compared One-class SVM, Isolation Forest (IF), and Local Outlier Factor (LOF). IF provides the best fault detection accuracy, 69.5%.

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.

Gain reduction mechanism observed in Low Gain Avalanche Diodes

Low Gain Avalanche Diodes (LGADs) is one of the candidate sensing technologies for future 4D-tracking applications and recently have been qualified to be used in the ATLAS and CMS timing detectors for the CERN High Luminosity Large Hadron Collider upgrade. LGADs can achieve an excellent timing performance by the presence of an internal gain that improves the signal-to-noise ratio leading to a better time resolution.These detectors are designed to exhibit a moderate gain with an increase of the reverse bias voltage. The value of the gain strongly depends on the temperature. Thus, these two values must be kept under control in the experiments to maintain the gain within the required values. A reduction in the reverse bias or an increase in the temperature will reduce the gain significantly.In this paper, a mechanism for gain reduction in LGADs is going to be presented. It was observed, that the gain measured in these devices depends on the charge density projected into the gain layer, generated by a laser or a charged particle in their bulk. Measurements performed with different detectors showed that ionizing processes that induce more charge density in the detector bulk lead to a decrease in the detector’s measured gain.Measurements conducted with an IR-laser and a Sr-90 in the lab, modifying the charge density generated in the detector bulk, confirmed this mechanism and will be presented here.

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.

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.

Study of the ATLAS new small wheel read-out controller ASIC in a neutron irradiation environment

Following the Large Hadron Collider upgrade phase from 2019-2020, the innermost station of the ATLAS Muon Spectrometer is being replaced with a newly enhanced detector system. The new associated electronic system will provide improved precision tracking and triggering for the expected high background rates. In this system, the Read-Out Controller (ROC) ASIC is an essential on-detector custom real-time data packet processor. It buffers, filters and aggregates the digitized data from up to 512 upgraded muon detectors and distributes phase-adjustable clock signals and control commands. It is fundamental to verify the robustness of ROC and its data integrity despite the neutron dose at which it is expected to be exposed. This paper briefly describes the ROC architecture, data formats, die layout and implemented techniques for the mitigation of radiation effects. The ROC test apparatus and irradiation testing are thoroughly presented, giving emphasis to the immunity to the produced single event upsets (SEUs) and the effects of data corruption inside its SRAM. Two ROC samples were subjected to neutron beams with 20, 22 and 24 MeV energies, for over 39 hours, at an average flux of 9.5 × 105 n⋅cm−2⋅s−1, totaling a dose equivalent to 8 months of operation in LHC at L = 1034 cm−2⋅s−1. Flip-Flops were affected by 69 SEUs yet the ROC operation was not disturbed by this, but data corruption in memories occurred with a considerable rate. Statistics of the resulting errors are presented.

Humidity sensitivity of large area silicon sensors: Study and implications

The production of large area sensors is one of the main challenges that the ATLAS collaboration faces for the new Inner-Tracker full-silicon detector. During the prototype fabrication phase for the High Luminosity Large Hadron Collider upgrade, several ATLAS institutes observed indications of humidity sensitivity of large area sensors, even at relative humidities well below the dew point. Specifically, prototype Barrel and End-Cap silicon strip sensors fabricated in 6-inch wafers manifest a prompt decrease of the breakdown voltage when operating under high relative humidity, adversely affecting the performance of the sensors. In addition to the investigation of these prototype sensors, a specific fabrication batch with special passivation is also studied, allowing for a deeper understanding of the responsible mechanisms.This work presents an extensive study of this behaviour on large area sensors. The locations of the hotspots at the breakdown voltage at high humidity are revealed using different infrared thermography techniques. Several palliative treatments are attempted, proving the influence of sensor cleaning methods, as well as baking, on the device performance, but no improvement on the humidity sensitivity was achieved. Furthermore, a study of the incidence of the sensitivity in different batches is also presented, introducing a hypothesis of the origins of the humidity sensitivity associated to the sensor edge design, together with passivation thickness and conformity. Several actions to be taken during sensor production and assembly are extracted from this study, in order to minimize the impact of humidity sensitivity on the performance of large area silicon sensors for High Energy Physics experiments.

Design, Implementation, and Experimental Verification of 5 Gbps, 800 Mrad TID and SEU-Tolerant Optical Modulators Drivers

This paper presents the design and experimental verification of two drivers designed to be compliant with the high radiation dose levels present in the inner layers of the CERN’s Large Hadron Collider (LHC) experimental chambers. The drivers, designed to face up to 800 Mrad (SiO2) Total Ionizing Dose, are able to sustain up to 5 Gbps bit-rate links when integrated in a 65 nm CMOS technology. They are designed to drive two Silicon Photonics optical modulators, Mach Zehnder Modulator and Ring Resonator, which have shown high rad-tolerant levels. The high dose level hardness of the drivers has been achieved by adopting the following Radiation Hardening By Design (RHBD) techniques: enhancement of the MOSFETs model to take into account the effects of high radiation dose levels and of single event effects on the devices, avoidance of using P-MOSFETs, increase of the minimum MOSFET lengths for the switching devices, and the use of Enclosed Layout Transistors shape plus some layout precautions. Moreover, to increase the drivers speed, techniques like buffer chain and inductive peaking are used in the drivers’ design. The experimental results have verified the matching of the high-speed high-voltage constraint required by the application. The Total Ionization Dose tests have shown, at 800 Mrad (SiO2), a 30% and 25% amplitude reduction of the output signals eye diagrams of the Mach Zehnder Modulator driver and of the Ring Resonator driver, respectively. In the worst case, in which the drivers will be placed within 5 cm from the beamline of the CMS experiment of the upgraded LHC, the heavy ions tests have shown a BER of 5.19e-8.

US contribution to the High Luminosity LHC Upgrade: focusing quadrupoles and crab cavities

In the early 2000’s, the US High Energy Physics community contributing to the Large Hadron Collider (LHC) launched the LHC Accelerator R&D Program (LARP), a long-vision focused R&D program, intended to contribute to a quick LHC commissioning and to bring the Nb3Sn and other technologies to a maturity level that would allow applications in HEP machines. Around 2015, the technologies developed by LARP, CERN and other institutions were mature enough to allow the spin-off of a major upgrade project to the LHC complex, the High Luminosity LHC (HL-LHC) [3]. This paper will focus on the US contribution to HL-LHC, namely the large-aperture low-β focusing Nb3Sn quadrupoles and the Radio Frequency Dipole (RFD) Crab Cavities, located in close proximity to the ATLAS and CMS experiments. This contribution, called the HL-LHC Accelerator Upgrade Project (HL-LHC AUP), focuses on production of these quadrupoles and cavities by sharing the work among a consortium of US Laboratories (FNAL, LBNL, BNL and SLAC) and Universities and in close connection with the CERN-led HL-LHC Collaboration. The collaboration achieved commonality of specifications and uniformity of performance. Final development of design, construction and first results from the prototypes are described to indicate the status of these critical components for HL-LHC.

Application of the New Generic Quench Detection System for LHC's 11 T Dipole Magnet

The high luminosity upgrade of large hadron collider (LHC) introduces a large number of new superconducting elements of various technologies. In order to ensure protection of these elements, a modular, versatile quench detection system had been developed. Designed to be flexible enough to detect quenches in superconducting bus-bars as well as in magnets, one generic base system is applied to various detection tasks. The fully customized system is based on a field programmable gate array that is connected to 16 galvanically insulated front-end channels. Due to the presence of radiation in some of the dedicated installation areas, the system is designed to be radiation tolerant up to 1 Gy/y. The first application of this system is the 11 T dipole magnet in Nb3Sn technology, which is foreseen to be installed during LHC's long shutdown 2. To gain experience with magnets made with this superconductor, which had not been used in LHC so far, the development of the detection system follows the tests of the magnet prototypes. Especially, the mitigation of flux jumps to avoid false triggers is a challenge for the system. A description of the hardware and firmware is given. Measurements from the recent magnet prototype and mitigation techniques against electrical oscillations are presented.

Transient Heat Transfer in Superfluid Helium Cooled Nb&lt;inline-formula&gt; &lt;tex-math notation="LaTeX"&gt;$_3$&lt;/tex-math&gt; &lt;/inline-formula&gt;Sn Superconducting Coil Samples

An experimental setup is operational at the Central Cryogenics Laboratory of the European Organization for Nuclear Research to measure the cooling mechanisms of superfluid 4 He (He II) from prepared Rutherford-type superconducting cable stacks to a stagnant He II bath. For novel magnets designed for the so-called high-luminosity large hadron collider upgrade, a segment of a fully impregnated Nb 3 Sn 11T dipole magnet was measured. A dataset on the thermal behavior is presented, with homogeneous heat inputs of up to approximately 4.8 mW cm -3 corresponding to an average steady-state temperature of 3.1 K for the inner layer and 4.0 K for the outer layer when cooled via a 1.9 K He II bath. We discuss the steady state as well as transient behavior observed.

FCC-hh: The Hadron Collider

In response to the 2013 Update of the European Strategy for Particle Physics (EPPSU), the Future Circular Collider (FCC) study was launched as a world-wide international collaboration hosted by CERN. The FCC study covered an energy-frontier hadron collider (FCC-hh), a highest-luminosity high-energy lepton collider (FCC-ee), the corresponding 100 km tunnel infrastructure, as well as the physics opportunities of these two colliders, and a high-energy LHC, based on FCC-hh technology. This document constitutes the third volume of the FCC Conceptual Design Report, devoted to the hadron collider FCC-hh. It summarizes the FCC-hh physics discovery opportunities, presents the FCC-hh accelerator design, performance reach, and staged operation plan, discusses the underlying technologies, the civil engineering and technical infrastructure, and also sketches a possible implementation. Combining ingredients from the Large Hadron Collider (LHC), the high-luminosity LHC upgrade and adding novel technologies and approaches, the FCC-hh design aims at significantly extending the energy frontier to 100 TeV. Its unprecedented centre of-mass collision energy will make the FCC-hh a unique instrument to explore physics beyond the Standard Model, offering great direct sensitivity to new physics and discoveries.

HE-LHC: The High-Energy Large Hadron Collider

In response to the 2013 Update of the European Strategy for Particle Physics (EPPSU), the Future Circular Collider (FCC) study was launched as a world-wide international collaboration hosted by CERN. The FCC study covered an energy-frontier hadron collider (FCC-hh), a highest-luminosity high-energy lepton collider (FCC-ee), the corresponding 100 km tunnel infrastructure, as well as the physics opportunities of these two colliders, and a high-energy LHC, based on FCC-hh technology. This document constitutes the third volume of the FCC Conceptual Design Report, devoted to the hadron collider FCC-hh. It summarizes the FCC-hh physics discovery opportunities, presents the FCC-hh accelerator design, performance reach, and staged operation plan, discusses the underlying technologies, the civil engineering and technical infrastructure, and also sketches a possible implementation. Combining ingredients from the Large Hadron Collider (LHC), the high-luminosity LHC upgrade and adding novel technologies and approaches, the FCC-hh design aims at significantly extending the energy frontier to 100 TeV. Its unprecedented centre-of-mass collision energy will make the FCC-hh a unique instrument to explore physics beyond the Standard Model, offering great direct sensitivity to new physics and discoveries.

Design optimization and evaluation of the 3 kA MgB2 cable at 4.3 K for the superconducting link project at CERN

High-current superconducting links (SC links) are being developed at CERN for powering the superconducting magnets of the High-Luminosity Large Hadron Collider upgrade. The links contain MgB2 cables, each about 100 m long, rated at currents of up to 18 kA. The assembly of the cables is carried out with reacted wires; cable geometry and cabling processes take into account the mechanical properties of the reacted MgB2 conductor. The production of the cables as well as their final installation requires good mechanical stability, flexibility and electrical performance. The superconductor should have good mechanical strength in view of the stresses during cabling (tension and bending), operation at cryogenic temperatures (Lorentz forces and thermal contraction) and handling installation (tension and bending) at room temperature. Moreover, the electrical integrity of the MgB2 wire (IC degradation ≤5%) should be ensured after the cabling process for the SC links. Therefore, the study of the mechanical properties of the MgB2 wire and the definition of the cable design parameters are crucial for the project. In the present work we report on the optimization and validation of the design of the 18-strand, 3 kA MgB2 cable by assessing the electromechanical behaviour of 3 kA MgB2 superconducting cables produced with different cabling parameters. The critical current (IC) of the MgB2 wires was measured after triple bending and axial tensile load, and strands extracted from the cables were tested to quantify the critical current degradation. Electrical measurements of two, 2 m long, 18-strand MgB2 cables were carried out in the FRESCA test facility at CERN and no degradation was observed. Cabling parameters such as the bending radius and the twist pitch were evaluated, and the most appropriate geometries for the MgB2 18-strand cables have been selected. Numerical simulations were performed to allow a detailed study of the strains developed in the MgB2 strands due to the mechanical loading. The present results have been successfully transferred to industry for the first industrial production in the framework of the SC Link project.