Search

During some periods in its second physics run (2015-2018), the LHC has been operated with 208Pb⁸²⁺ ion beams at an energy of 6.37 ZTeV. The LHC is equipped with a betatron collimation system, which intercepts the transverse beam halo and protects sensitive equipment such as superconducting magnets against beam losses. However, hadronic fragmentation and electromagnetic dissociation of heavy ions in collimators generate off-rigidity particles, which can be lost in the downstream dispersion suppressor, putting the magnets at risk to quench. An accurate modelling of the beam-induced energy deposition in the collimation system and superconducting magnets is important for quantifying possible performance limitations arising from magnet quenches. In this paper, we compare FLUKA shower simulations against beam loss monitor measurements recorded during the 2018 208Pb⁸²⁺ run. In particular, we investigate fast beam loss events, which lead to recurring beam aborts in 2018 operation. Based on these studies, we assess the ability of the simulation model to reproduce the observed loss patterns in the collimation region and dispersion suppressor., Proceedings of the 13th International Particle Accelerator Conference, IPAC2022, Bangkok, Thailand

Understanding and mitigating particle losses in the Large Hadron Collider (LHC) is essential for both machine safety and efficient operation. Abnormal loss distributions are telltale signs of abnormal beam behaviour or incorrect machine configuration. By leveraging the advancements made in the field of Machine Learning, a novel data-driven method of detecting anomalous loss distributions during machine operation has been developed. A neural network anomaly detection model was trained to detect Unidentified Falling Object events using stable beam, Beam Loss Monitor (BLM) data acquired during the operation of the LHC. Data-driven models, such as the one presented, could lead to significant improvements in the autonomous labelling of abnormal loss distributions, ultimately bolstering the ever ongoing effort toward improving the understanding and mitigation of these events., Proceedings of the 13th International Particle Accelerator Conference, IPAC2022, Bangkok, Thailand

Among the various future lepton colliders under study, muon colliders offer the prospect of reaching the highest collision energies. Despite the promising potential of a multi-TeV muon collider, the short lifetime of muons poses a severe technological challenge for the collider design. In particular, the copious production of decay electrons and positrons along the collider ring requires the integration of continuous radiation absorbers inside superconducting magnets. The absorbers are needed to avoid quenches, reduce the heat dissipation in the cold mass and prevent magnet failures due to long-term radiation damage. In this paper, we present FLUKA shower simulations assessing the shielding requirements for high-field magnets of a 10 TeV muon collider. We quantify in particular the role of synchrotron photon emission by decay electrons and positrons, which helps in dispersing the energy carried by the decay products. For comparison, selected results for a 3 TeV muon collider are also presented., Proceedings of the 13th International Particle Accelerator Conference, IPAC2022, Bangkok, Thailand

The LHC heavy-ion program with 208Pb⁸²⁺ beams is foreseen to benefit from a significant intensity upgrade in 2022. A performance limitation may arise from ion fragments scattered out of the collimators in the betatron cleaning insertion, which risk quenching superconducting magnets during periods of short beam lifetime. In order to mitigate this risk, an alternative collimation technique, relying on bent crystals as primary collimators, will be used in future heavy-ion runs. In this paper, we study the power deposition in superconducting magnets by means of FLUKA shower simulations, comparing the standard collimation system against the crystal-based one. The studies focus on the dispersion suppressor regions downstream of the betatron cleaning insertion, where the ion fragment losses are the highest. Based on these studies, we quantify the expected quench margin expected in future runs with 208Pb⁸²⁺ beams., Proceedings of the 13th International Particle Accelerator Conference, IPAC2022, Bangkok, Thailand

Muon colliders offer enormous potential for research of the particle physics frontier. Leptons can be accelerated without suffering large synchrotron radiation losses. The International Muon Collider Collaboration is considering 3 and 10 TeV (CM) machines for a conceptual stage. In the core of the Muon Collider facility lays a MW class production target, which will absorb a high power (1 and 3 MW) proton beam to produce muons via pion decay. The target must withstand high dynamic thermal loads induced by 2 ns pulses at 5-50 Hz. Also, operational reliability must be guaranteed to reduce target exchanges to a minimum. Several technologies for these systems are being studied in different laboratories. We present in this paper the results of a preliminary feasibility study of a graphite-based target, and the different layouts under study for a demonstrator target complex at CERN. Synergies with advanced nuclear systems are being explored for the development of a liquid metal target., Proceedings of the 13th International Particle Accelerator Conference, IPAC2022, Bangkok, Thailand

The international FCC study group published in 2019 a Conceptual Design Report for an electron-positron collider with a centre-of-mass energy from 90 to 365 GeV with a beam currents of up to 1.4 A per beam. The high beam current of this collider create challenging requirements on the injection chain and all aspects of the linac need to be carefully reconsidered and revisited, including the injection time structure. The entire beam dynamics studies for the full linac, damping ring and transfer lines are major activities of the injector complex design. A key point is that any increase of positron production and capture efficiency reduces the cost and complexity of the driver linac, the heat and radiation load of the converter system, and increases the operational margin. In this paper we will give an overview of the status of the injector complex design and introduce the new layout that has been proposed by the study group working in the context of the CHART collaboration. In this framework, furthermore, we also present the preliminary studies of the FCC-ee positron source highlighting the main requirements and constraints., Proceedings of the 13th International Particle Accelerator Conference, IPAC2022, Bangkok, Thailand

The Future Circular electron-positron Collider (FCC-ee) will have stored beam energies of up to 20 MJ. This is a factor 100 higher than any current or past lepton collider. A safe and reliable disposal of the beam onto a beam dump block is therefore critical for operation. To ensure the survival of the dump core blocks, transversal dilution of the beam is necessary. To reduce the complexity of the system and guarantee high availability, an optimized, semi-passive beam dumping system has been designed. The main dump absorber design has been optimized following recent studies for high energy dump block materials for the LHC High Luminosity upgrade. First simulations regarding the radiation environment of the dumping system have been carried out, allowing the definition of preliminary constraints for the integration with respect to radiation sensitive equipment. The performance of the system has been evaluated using Monte-Carlo simulations as well as thermomechanical Finite-Element-Analysis to investigate potential material failure and assess safety margins. An experiment at the CERN HiRadMat facility has been carried out and preliminary results show good agreement with simulations., Proceedings of the 13th International Particle Accelerator Conference, IPAC2022, Bangkok, Thailand

The beam stored energy and the peak intensity of CERN Large Hadron Collider (LHC) will grow in the next few years. The former will increase from the 320 MJ values of Run2 (2015-2018) to almost 540 MJ during Run3 (2022 onwards) and 680 MJ during the HL-LHC era putting stringent requirements on beam intercepting devices, such as absorbers and dumps. The HiRadMat-56-HED (High-Energy Dumps) experiment performed in Autumn 2021 executed at CERN HiRadMat facility employed the Super Proton Synchrotron accelerator (SPS) 440 GeV/c proton beam to impact different low-density carbon-based materials targets to assess their performance to these higher energy beam conditions. The study focused on advanced grades of graphitic materials, including isostatic graphite, carbon-fiber reinforced carbon and carbon-SiC materials in addition to flexible expanded graphite. Some of them specifically tailored in collaboration with industry to very specific properties. The objectives of this experiment are: (i) to assess the performance of existing and potentially suitable advanced materials for the currently operating LHC beam dumps and (ii) to study alternative materials for the HL-LHC main dump or for the Future Circular Collider dump systems. The contribution will detail the R phase during design, the execution of the experiment, the pre-irradiation tests as well as the first post irradiation examination of the target materials. Lessons learnt and impact on operational devices will also be drawn., Proceedings of the 13th International Particle Accelerator Conference, IPAC2022, Bangkok, Thailand

For an electron-positron collider like FCC-ee, the production of positrons plays a crucial role. One of the design options considered for the FCC-ee positron source employs a superconducting solenoid made of HTS coils as an adiabatic matching device. The solenoid, which is placed around the production target, is needed to capture positrons before they can be accelerated in a linear accelerator. A superconducting solenoid yields a higher peak field than a conventional-normal conducting magnetic flux concentrator, therefore increasing the achievable positron yield. In order to achieve an acceptable positron production, the considered target is made of tungsten-rhenium, which gives also a significant flux of un-wanted secondary particles, that in turn could generate a too large radiation load on the superconducting coils. In this study, we assess the feasibility of such a positron source by studying the heat load and long-term radiation damage in the superconducting matching device and surrounding structures. Results are presented for different geometric configurations of the superconducting matching device., Proceedings of the 13th International Particle Accelerator Conference, IPAC2022, Bangkok, Thailand

After its second successful run period, the Large Hadron Collider (LHC) shut down for three years with the plan of being recommissioned in 2022 for a three-year physics production period, the Run 3. The future restart of the machine coincides with the completion of the LHC Injectors Upgrade (LIU) project, offering to the LHC the opportunity and the challenge to operate with up to two times higher beam brightness, pending the complete installation of the High-Luminosity LHC (HL-LHC), which should take place in Long Shutdown 3 (LS3). In this context, Run 3 is clearly a transition between the LHC and the HL-LHC, with key ingredients which will be made available, either gradually (LIU beam) or immediately (ATS optics). Run 3 shall therefore be exploited not only for performance, but also as a full scale demonstrator of the HL-LHC in terms of beams, optics and beam manipulation (e.g. β∗ levelling over a very large dynamic range). To this aim, the so-called LHC configuration, namely the optics, needs to be adapted in order to cope or mitigate constraints of different nature, from beam brightness limitations due to the machine impedance, to specific desiderata of some LHC experiments. After reviewing these constraints, including the intensity limitations coming from the existing hardware, the beam parameters targeted for the LHC in Run 3 are given. A possible solution for the machine configuration will then be described, and analyzed from various perspectives, which should not limit the machine performance over the full Run 3, and should enable to double the integrated luminosity delivered so far to the two high luminosity insertions of the LHC.

During CERN’s LS2, several upgrades were performed to beam intercepting devices in the framework of the HL-LHC Project. Upgraded equipment includes two internal beam dumps (TDIS) intended for machine protection located at the injection points from the SPS to the LHC. These two devices have been assembled, tested, and installed around LHC Point 2 and Point 8 and are currently ready to get commissioned with the beam. They are 5.8m-long, three-module-segmented vacuum chambers, with large aperture to accommodate the injected and circulating beam and equipped with absorbing materials, These comprise graphite and higher Z alloys that are embedded on sub-assemblies reinforced with back-stiffeners made of TZM. The current contribution covers three main matters. First, it details the TDIS design and its key technical features. The second topic discussed is the outcome of an experiment where a prototype module was tested under high-energy beam impacts at CERN’s HiRadMat facility. To conclude it is presented the return of experience from the pre-series construction, validation and installation in the LHC tunnel., Proceedings of the 12th International Particle Accelerator Conference, IPAC2021, Campinas, SP, Brazil

For the first time, a full characterization of the Pb-Pb and Pb-p collision debris as well as its impact in terms of energy deposition in the long straight section (LSS) of CERN’s Large Hadron Collider has been carried out. By means of Monte Carlo simulations with FLUKA, both inelastic nuclear interaction and electromagnetic dissociation were taken into account as source term for lead ion operation, while for Pb-p operation only nuclear interaction is of importance. The radiation exposure of detectors exclusively destined for ion beam runs is assessed, allowing drawing implications of their use. This work gave the opportunity for an unprecedented validation of simulation results against measurement of beam loss monitors (BLM) in the experimental LSS during ion operation. Pb-Pb operation refers to the 2018 ion run at 6.37 TeV per charge with a +160 microrad half crossing angle in the vertical plane at the ATLAS interaction point. Instead, Pb-p operation was benchmarked for the 2016 ion run at 6.5 TeV per charge with -140 microrad half crossing angle in the vertical plane at the same location., Proceedings of the 12th International Particle Accelerator Conference, IPAC2021, Campinas, SP, Brazil

The power deposited in dispersion suppressor magnets downstream of the Large Hadron Collider (LHC) betatron cleaning insertion is governed by off-momentum particles scattered out of the primary collimators. In order to mitigate the risk of magnet quenches during periods of short beam lifetime in future High-Luminosity (HL-LHC) operation, new dispersion suppressor (DS) collimators are considered for installation (one per beam). In this paper, we present FLUKA simulations for both protons and Pb ions at 7 TeV, predicting the power deposition in the DS magnets, including the new higher-field dipoles 11T which are needed to integrate the collimator in the cold region next to the cleaning insertion. The simulated power deposition levels for the adopted HL-LHC collimator configuration and settings are used to assess the quench margin by comparison with the present estimated quench levels., Proceedings of the 12th International Particle Accelerator Conference, IPAC2021, Campinas, SP, Brazil

The Large Hadron Collider (LHC) beam dump (TDE) is essential for safe and reliable operation of the collider. It absorbs particles extracted from the accelerator whenever required. The original design of the TDE dates from the mid 2000 and it is constituted of an eight-meter-long cylindrical stainless-steel tube, filled with low-Z carbon-based materials from different grades and densities. The Sigraflex®, an expanded low-density graphite, is employed in the middle section of the TDE core. Due to unexpected behaviour observed in the past LHC runs, several major upgrades were recently implemented in order for the TDE to be ready for LHC Run3 (2021-2024), where up to 555 MJ beam energy is expected to be dumped every few hours. According simulations, temperatures in the Sigraflex core will reach locally up to 1500°C in the regular dump cases, and above 2300°C for failure scenarios. The objective of this contribution is to summarize the LS2 hardware upgrades and the plan for the evaluation of the Sigraflex performance during LHC Run3. This work will also detail the last experimental and numerical findings applied to the Sigraflex®, and possible alternative materials for the future., Proceedings of the 12th International Particle Accelerator Conference, IPAC2021, Campinas, SP, Brazil

To avoid any damage to the beam dump target in the Future Circular Collider, the beam will be swept over its surface using oscillating kickers in the x/y planes with a 90-degree phase difference, and an amplitude changing in time, creating a spiral pattern. The ideal pattern must have an increasing spiral pitch towards smaller radii to produce an even energy deposition density. We recommend the realization of the optimal pattern using two beating frequencies. This method enables a flat energy deposition density while only using simple independent damped oscillators. In this poster, we also present the study of the beamline optics and hardware that can realize the needed pattern. Two different possible hardware layouts were examined and optimized as well., Proceedings of the 12th International Particle Accelerator Conference, IPAC2021, Campinas, SP, Brazil

After the High Luminosity (HL-LHC) upgrade, the LHC will be exposed to a higher risk of magnet quenches during periods of short beam lifetime. Collimators in the extraction region (IR6) assure the protection of magnets against asynchronous beam dumps, but they also intercept a fraction of the beam halo leaking from the betatron cleaning insertion. In this paper, we assess the risk of quenching nearby quadrupoles during beam lifetime drops. In particular, we present an empirical analysis of halo losses in IR6 using LHC Run 2 (2015-2018) beam loss monitor measurements. Based on these results, the halo-induced power density in magnet coils expected in HL-LHC is estimated using FLUKA Monte Carlo shower simulations., Proceedings of the 12th International Particle Accelerator Conference, IPAC2021, Campinas, SP, Brazil

This MD allowed confirming that the solenoid installed in 16L2 during Technical Stop 2 (TS22017) could be held responsible for the performance improvement observed after TS2. The MD was performed on 30th November 2017 in parallel with MD#2889 and the procedure was adjusted for both MDs to profit as much as possible of the available time.

This note summarises the LHC Machine Development (MD) 4044, which studied the beam-loss and quench behaviour during asynchronous beam dumps at injection and at top energy using bunched beam in the abort gap. The main MD results are presented together with energy-deposition studies and calculations of the relevant quench limits.

This note summarises the results of LHC Machine Development (MD) 2930, which studied the beam-loss behaviour during asynchronous beam dumps at 450 GeV and at 6.5 TeV using bunched beam in the abort gap. The MD consisted of three main parts. First, single pilot bunches were injected into the abort gap, dumped and the resulting beam loss patterns were recorded. Second, trains of 48 bunches were injected into the abort gap with successively increasing bunch intensity and dumped. No quenches of superconducting magnets were observed up to a bunch intensity of 1.25e11 protons. In the last part, single pilots were ramped to 6.5 TeV. The last dump caused the beam-induced quench of the MQY.4R6, the MB.A8R6 and the MQY.4L6 magnets.

A variety of processes can cause unavoidable beam losses during normal and abnormal beam operation. Because of the high stored energy of about 700 MJ and the small transverse beam sizes, the HL-LHC beams are highly destructive. Even a local beam loss of a tiny fraction of the full beam in a superconducting magnet could cause a quench, and larger beam losses could cause damage to accelerator components. Therefore, all beam losses must be tightly controlled. For this purpose, a multistage collimation system has been installed, to safely dispose of beam losses. Unlike other high-energy colliders, where the main purpose of collimation is typically to reduce experimental backgrounds, the LHC and the HL-LHC require efficient beam collimation during all stages of operation from injection to top energy. The requirement to operate efficiently and safely with high-intensity hadron beams at small colliding beam sizes provides significant challenges, which drive the key design aspects of the collimation system at the HL-LHC.

The beam transfer into the LHC is achieved by the two transfer lines TI2 and TI8, together with the septum and injection kickers, plus associated systems to ensure the protection of the LHC elements in case of a mis- steered beam. The foreseen increase in injected intensity and brightness for the HL-LHC means that the protection functionality of the beam-intercepting devices (TDI) needs upgrading. In addition, the higher beam current significantly increases the beam-induced power deposited in many elements, including the injection kicker magnets in the LHC ring. The beam dumping system is also based on DC septa and fast kickers, with various beam intercepting protection devices including the beam dump block. Again, the significant change in the beam parameters for the HL-LHC implies redesign of several of the dump system devices, both because of the increased energy deposition in the case of direct impact and because of increased radiation background that could affect the reliability of this key machine protection system.

Micrometer sized particles (UFOs) entering the beam are a known cause of localized beam losses since the beginning of high intensity beam operation, however the origin of these particles is not fully known. Furthermore, during 2017 a new type of UFO events appeared around the 16L2 interconnection in the LHC, leading to beam instabilities resulting in major impact on beam availability. In MD#2036 a proof-of-concept method utilizing blown-up bunches and a fast loss detection system for studying the dynamics of UFOs, simulated by the wirescanners, was successfully attempted. In this MD it was shown that real UFO dynamics are possible to study employing this method. The MD was done in parallel with MD#2934 and the procedure was adjusted for both MDs to profit as much as possible. In the end a single 16L2 induced beam dump occurred, but several conclusions about the UFO dynamics can already be drawn.

This report discusses the feasibility and limitations for operating the LHC and HL-LHC at the ultimate beam energy of 7.5 TeV, corresponding to a main dipole magnetic field of 8.93 T and an operating current of 12748 A.

The HL-LHC upgrade baseline foresees to replace all secondary collimators of IR7 until LS3 in order to ensure a sufficient margin for beam stability with the high-brightness upgraded beams. The present TCSG design is based on a carbon-fibre composite (CFC) material and will be replaced with a new low-impedance design (TCSPM). The TCSPM design is based on a Molybdenum-Graphite (MoGr) composite material coated with pure Molybdenum. These collimators also embed in-jaw beam position monitors (BPMs) for a fast alignment and local orbit monitoring as well as an additional BPM for measurements of the orbit transverse to the collimation pane. A staged deployment strategy of the low-impedance upgrade is proposed that foresees to install 4 TCSPM collimators per beam in LS2 and the remaining 7 in LS3. In this note, the slots to be equipped with the TCSPM in LS2 are defined.