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| TUPMW006 | Power Deposition in LHC Magnets Due to Bound-Free Pair Production in the Experimental Insertions | 1418 |
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| The peak luminosity achieved during Pb-Pb collisions in the LHC in 2015 (3x1027cm-2s−1) well exceeded the design luminosity and is anticipated to increase by another factor 2 after the next Long Shutdown (2019- 2020). A significant fraction of the power dissipated in ultra-peripheral Pb-Pb collisions is carried by ions from bound-free pair production, which are lost in the dispersion suppressors adjacent to the experimental insertions. At higher luminosities, these ions risk to quench superconducting magnets and might limit their operation due to the dynamic heat load that needs to be evacuated by the cryogenic system. In this paper, we estimate the power deposition in superconducting coils and the magnet cold mass and we quantify the achievable reduction by deviating losses to less sensitive locations or by installing collimators at strategic positions. The second option is considered for the dispersion suppressor next to the ALICE insertion, where a selective displacement of losses to a magnet-free region is not possible. | ||
| DOI • | reference for this paper ※ DOI:10.18429/JACoW-IPAC2016-TUPMW006 | |
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| TUPMW007 | Impact of Long Range Beam-Beam Effects on Intensity and Luminosity Lifetimes from the 2015 LHC Run | 1422 |
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Funding: Research supported by the High Luminosity LHC project Luminosity is one of the key parameters that determines the performance of colliding beams in the Large Hadron Collider (LHC). Luminosity can therefore be used to quantify the impact of beam-beam interactions on the beam lifetimes and emittances. The High Luminosity Large Hadron Collider (HL-LHC) project aims to reach higher luminosities, approximately a factor of 7 larger than the nominal LHC at peak luminosity without crab cavities. Higher luminosities are achieved by increasing the bunch populations and reducing the transverse beam sizes. This results in stronger beam-beam effects. Here the LHC luminosity and beam intensity decay rates are analysed as a function of reducing beam separation with the aim of characterising the impact of beam-beam effects on the luminosity and beam lifetime. The analysis and results are discussed with possible application to the HL-LHC upgrade. |
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| DOI • | reference for this paper ※ DOI:10.18429/JACoW-IPAC2016-TUPMW007 | |
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| TUPMW014 | Improved Aperture Measurements at the LHC and Results from their Application in 2015 | 1446 |
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| A good knowledge of the available aperture in the LHC is essential for a safe operation due to the risk of magnet quenches or even damage in case of uncontrolled beam losses. Experimental validations of the available aperture are therefore crucial and were in the past carried out by either a collimator scan combined with beam excitations or through the use of local orbit bumps. In this paper, we show a first comparison of these methods in the same machine configuration, as well as a new very fast method based on a beam-based collimator alignment and a new faster variant of the collimator scan method. The methods are applied to the LHC operational configuration for 2015 at injection and with squeezed beams and the measured apertures are presented. | ||
| DOI • | reference for this paper ※ DOI:10.18429/JACoW-IPAC2016-TUPMW014 | |
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| TUPMW015 | Symplectic Tracking of Multi-Isotopic Heavy-Ion Beams in SixTrack | 1450 |
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Funding: Work suppported by the Wolfgang Gentner Programme of the German BMBF The software SixTrack provides symplectic proton tracking over a large number of turns. The code is used for the tracking of beam halo particles and the simulation of their interaction with the collimators to study the efficiency of the LHC collimation system. Tracking simulations for heavy-ion beams require taking into account the mass to charge ratio of each particle because heavy ions can be subject to fragmentation at their passage through the collimators. In this paper we present the derivation of a Hamiltonian for multi-isotopic heavy-ion beams and symplectic tracking maps derived from it. The resulting tracking maps were implemented in the tracking software SixTrack. With this modification, SixTrack can be used to natively track heavy-ion beams of multiple isotopes through a magnetic accelerator lattice. |
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| DOI • | reference for this paper ※ DOI:10.18429/JACoW-IPAC2016-TUPMW015 | |
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| TUPMW021 | Roman Pot Insertions in High-Intensity Beams for the CT-PPS Project at LHC | 1473 |
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| The CMS-TOTEM Precision Proton Spectrometer (CT-PPS) at the LHC IP5 aims at exploring diffractive physics at high luminosity in standard LHC fills. It is based on 14 Roman Pots (RPs), designed to host tracking and time-of-flight detectors for measuring the kinematics of leading protons. To reach the physics goals, the RPs will finally have to approach the beams to distances of 15 beam σs (i.e. ~1.5 mm) or closer. After problems with showers and impedance heating in first high-luminosity RP insertions in 2012, the LS1 of LHC was used for upgrades in view of impedance minimisation and for adding new collimators to intercept RP-induced showers. In 2015 the effectiveness of these improvements was shown by successfully inserting the RPs in all LHC beam intensity steps to a first-phase distance of ~25 σs. This contribution reviews the measurements of debris showers and impedance effects, i.e. the data from Beam Loss Monitors, beam vacuum gauges and temperature sensors. The dependences of the observables on the luminosity are shown. Extrapolations to L=1034 cm-2 s-1 and smaller distances to the beam do not indicate any fundamental problems. The plans for 2016 are outlined. | ||
| DOI • | reference for this paper ※ DOI:10.18429/JACoW-IPAC2016-TUPMW021 | |
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| TUPMW025 | Machine Protection from Fast Crab Cavity Failures in the High Luminosity LHC | 1485 |
| SUPSS005 | use link to see paper's listing under its alternate paper code | |
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| The time constant of a crab cavity (CC) failure can be faster than the reaction time of the active protection system. In such a scenario, the beams cannot be immediately extracted, making the the protection of the machine rely on the passive protection devices. At the same time, the energy stored in the High Luminosity (HL) LHC beams will be doubled with respect to the LHC to more than 700 MJ, which increases the risk of damaging the machine and the experiments in a failure scenario. In this study we estimate the impact that different CC failures have on the collimation system. We also give a first quantitative estimate of the effect of these failures on the elements near the experiments based on FLUKA simulations, using an updated HL-LHC baseline. | ||
| DOI • | reference for this paper ※ DOI:10.18429/JACoW-IPAC2016-TUPMW025 | |
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| TUPMW027 | The 2015 Heavy-Ion Run of the LHC | 1493 |
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| In late 2015 the LHC collided lead nuclei at a beam energy of 6.37 Z TeV, chosen to match the 5.02 TeV per colliding nucleon pair of the p-Pb collision run in 2013. In so doing, it surpassed its design luminosity by a factor of 2. Besides the higher energy, the operational configuration had a number of new features with respect to the previous Pb-Pb run at 3.5 Z TeV in 2011; unusual bunch patterns providing collisions in the LHCb experiment for the first time, luminosity levelling and sharing requirements, a vertical displacement of the interaction point in the ALICE experiment, and operation closer to magnet quench limits with mitigation measures. We present a summary of the commissioning and operation and what has been learned in view of future heavy-ion operation at higher luminosity. | ||
| DOI • | reference for this paper ※ DOI:10.18429/JACoW-IPAC2016-TUPMW027 | |
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| WEPMW006 | First Design of a Proton Collimation System for 50 TeV FCC-hh | 2423 |
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| We present studies aimed at defining a first conceptual solution for a collimation system for the hadron-hadron option for the Future Circular Collider (FCC-hh). The baseline collimation layout is based on the scaling of the present LHC collimation system to the FCC-hh energy. It currently includes a dedicated betatron cleaning insertion as well as collimators in the experimental insertions to protect the inner triplets. An aperture model for the FCC-hh is defined and the geometrical acceptance is calculated at top energy taking into account mechanical and optics imperfections. Based on these studies the collimator settings needed to protect the machine are defined. The performance of the collimation system is then assessed with particle tracking simulation tools assuming a perfect machine. | ||
| DOI • | reference for this paper ※ DOI:10.18429/JACoW-IPAC2016-WEPMW006 | |
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| WEPMW007 | Validation of Off-momentum Cleaning Performance of the LHC Collimation System | 2427 |
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| The LHC collimation system is designed to provide effective cleaning against losses coming from off-momentum particles, either due to un-captured beam or to an unexpected RF frequency change. For this reason the LHC is equipped with a hierarchy of collimators in IR3: primary, secondary and absorber collimators. After every collimator alignment or change of machine configuration the off-momentum cleaning efficiency is validated with loss maps at low intensity. We describe here the improved technique used in 2015 to generate such loss maps without completely dumping the beam into the collimators. The achieved performance of the collimation system for momentum cleaning is reviewed. | ||
| DOI • | reference for this paper ※ DOI:10.18429/JACoW-IPAC2016-WEPMW007 | |
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| WEPMW028 | First Attempts at using Active Halo Control at the LHC | 2486 |
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Funding: Research supported by the High Luminosity LHC project. The beam halo population is a non-negligible factor for the performance of the LHC collimation system and the machine protection. In particular this could become crucial for aiming at stored beam energies of 700 MJ in the High Luminosity (HL-LHC) project, in order to avoid beam dumps caused by orbit jitter and to ensure safety during a crab cavity failure. Therefore several techniques to safely deplete the halo, i.e. active halo control, are under development. In a first attempt a novel way for safe halo depletion was tested with particle narrow-band excitation employing the LHC Transverse Damper (ADT). At an energy of 450 GeV a bunch selective beam tail scraping without affecting the core distribution was attempted. This paper presents the first measurement results, as well as a simple simulation to model the underlying dynamics. |
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| DOI • | reference for this paper ※ DOI:10.18429/JACoW-IPAC2016-WEPMW028 | |
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| WEPMW029 | Simulation of Heavy-Ion Beam Losses with the SixTrack-FLUKA Active Coupling | 2490 |
| SUPSS008 | use link to see paper's listing under its alternate paper code | |
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Funding: Work suppported by the Wolfgang Gentner Programme of the German BMBF The LHC heavy-ion program aims to further increase the stored ion beam energy, putting high demands on the LHC collimation system. Accurate simulations of the ion collimation efficiency are crucial to validate the feasibility of new proposed configurations and beam parameters. In this paper we present a generalized framework of the SixTrack-FLUKA coupling to simulate the fragmentation of heavy-ions in the collimators and their motion in the LHC lattice. We compare heavy-ion loss maps simulated on the basis of this framework with the loss distributions measured during heavy-ion operation in 2011 and 2015. |
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| DOI • | reference for this paper ※ DOI:10.18429/JACoW-IPAC2016-WEPMW029 | |
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| WEPMW030 | Cleaning Performance of the Collimation System of the High Luminosity Large Hadron Collider | 2494 |
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| Different upgrades of the LHC will be carried out in the framework of the High Luminosity project (HL-LHC), where the total stored energy in the machine will increase up to about 700 MJ. This unprecedented stored energy poses serious challenges for the collimation system, which was designed to handle safely up to about 360 MJ. In this paper the baseline collimation layout for HL-LHC is described, with main focus on upgrades related to the cleaning of halo and physics debris, and its expected performance is discussed. The main upgrade items include the presence of new collimators in the dispersion suppressor of the betatron cleaning insertion installed between two 11 T dipoles, and two additional collimators for an improved local protection of triplet magnets. Thus, optimized settings for the entire and upgraded collimation chain were conceived and are shown here together with the resulting cleaning performance. Moreover, the cleaning performance taking into account crab cavities it is also discussed. | ||
| DOI • | reference for this paper ※ DOI:10.18429/JACoW-IPAC2016-WEPMW030 | |
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| WEPMW031 | Towards Optimum Material Choices for the HL-LHC Collimator Upgrade | 2498 |
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| The first years of operation at the LHC showed that collimator material-related concerns might limit the performance. In addition, the HL-LHC upgrade will bring the accelerator beyond the nominal performance through more intense and brighter proton beams. A new generation of collimators based on advanced materials is needed to match present and new requirements. After several years of R&D on collimator materials, studying the behaviour of novel composites with properties that address different limitations of the present collimation system, solutions have been found to fulfil various upgrade challenges. This paper describes the proposed staged approach to deploy new materials in the upgraded HL-LHC collimation system. Beam tests at the CERN HiRadMat facility were also performed to benchmark simulation methods and constitutive material models. | ||
| DOI • | reference for this paper ※ DOI:10.18429/JACoW-IPAC2016-WEPMW031 | |
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| WEPMW033 | Validation of Simulation Tools for Fast Beam Failure Studies in the LHC | 2506 |
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| The LHC collimation system protects passively the most sensitive machine equipment against beam losses. In particular, collimators are the last line of defense in case of single-turn failures that cannot be caught by the standard interlock system. The collimator settings are conceived to protect the machine even for very rare events, like beam abort failures with a full machine. Collimator settings are established in simulations through a dedicated tracking setup but also empirically validated by beam measurements at low intensities. A benchmark of simulations is essential for reliably estimating the response of the system for future machine configurations and beam parameters. In the paper, results are presented of tracking simulations for different optics deployed in the LHC Run II at 6.5 TeV and compared with data. | ||
| DOI • | reference for this paper ※ DOI:10.18429/JACoW-IPAC2016-WEPMW033 | |
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| WEPMW034 | First Operational Experience with Embedded Collimator BPMs in the LHC | 2510 |
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| During Long Shutdown 1, 18 Large Hadron Collider (LHC) collimators were replaced with a new design, in which beam position monitor (BPM) pick-up buttons are embedded in the collimator jaws. The BPMs provide a direct measurement of the beam orbit at the collimators, and therefore can be used to align the collimators more quickly than using the standard technique which relies on feedback from beam losses. Online orbit measurements also mean that margins in the collimation hierarchy placed specifically to cater for unknown orbit drifts can be reduced, therefore increasing the beta-star and luminosity reach of the LHC. In this paper, the first operational results are presented, including a comparison with the standard alignment technique and a fill-to-fill analysis of the measured orbit in different machine modes in the first year of running after the shutdown. | ||
| DOI • | reference for this paper ※ DOI:10.18429/JACoW-IPAC2016-WEPMW034 | |
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| WEPMW036 | MERLIN Cleaning Studies with Advanced Collimator Materials for HL-LHC | 2514 |
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| The challenges of the High-Luminosity upgrade of the Large Hadron Collider require improving the beam collimation system. An intense R&D program has started at CERN to explore novel materials for new collimator jaws to improve robustness and reduce impedance. Particle tracking simulations of collimation efficiency are performed using the code MERLIN which has been extended to include new materials based on composites. After presenting two different implementations of composite materials tested in MERLIN, we present simulation studies with the aim of studying the effect of the advanced collimators on the LHC beam cleaning. | ||
| DOI • | reference for this paper ※ DOI:10.18429/JACoW-IPAC2016-WEPMW036 | |
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| WEPMW037 | MERLIN Simulations of the LHC Collimation System with 6.5 TeV Beams | 2518 |
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| The accelerator physics code MERLIN has been extended in many areas to make detailed studies of the LHC collima- tion system and calculate loss maps from beam halo losses. Large scale tracking simulations have been produced for the 2015 run configuration at 6.5 TeV. We present results of cleaning inefficiency simulations of the LHC's multi-stage collimation system along with a detailed comparison be- tween MERLIN, SixTrack, and measured beam losses. | ||
| DOI • | reference for this paper ※ DOI:10.18429/JACoW-IPAC2016-WEPMW037 | |
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| WEPOY047 | LHC Collimation and Energy Deposition Studies Using Beam Delivery Simulation (BDSIM) | 3101 |
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| Beam Delivery Simulation (BDSIM) is a program that uses a suite of high energy physics software including Geant4, CLHEP & ROOT, that seamlessly tracks particles through accelerators and detectors utilising the full range of particles and physics processes from Geant4. A comparison of the collimator cleaning efficiency and energy deposition throughout the full length of the Large Hadron Collider (LHC) with the established SixTrack simulations of the CERN collimation group is presented. The propagation of the full hadronic showers from collimators provides unparalleled detail in energy deposition maps and these are compared with the data from beam loss monitors that measure radiation outside the magnet body. | ||
| DOI • | reference for this paper ※ DOI:10.18429/JACoW-IPAC2016-WEPOY047 | |
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| THPOY043 | Time Scale of Crab Cavity Failures Relevant for High Luminosity LHC | 4196 |
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Funding: Research supported by the High Luminosity LHC project A good knowledge of the effects of the crab cavities, required for the baseline High Luminosity LHC (HL-LHC), is needed before the results of the first tests of crab cavity prototypes in the SPS, planned for 2018, will be available. In case of crab cavity failures, we have to make sure that time scales are long enough so that the beams can be cleanly dumped before damage by beam loss occurs. We discuss our present knowledge and modeling of crab cavity induced beam losses, combined with mechanical deformation. We discuss lower limits on the time scales required for safe operation, and possible failure mitigation methods. |
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| DOI • | reference for this paper ※ DOI:10.18429/JACoW-IPAC2016-THPOY043 | |
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