| Paper | Title | Page |
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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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| 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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| 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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| WEPMW032 | Radiation-induced Effects on LHC Collimator Materials under Extreme Beam Conditions | 2502 |
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| Over the last years, several samples of present and novel LHC collimator materials were irradiated under various beam conditions (using protons, fast neutrons, light and heavy ions at different energies and fluences) in different facilities around the world. This was achieved through an international collaboration including many companies and laboratories over the world. The main goal of the beam tests and the post-irradiation campaign is the definition of a threshold for radiation damage above which LHC collimators need to be replaced. In this paper, highlights of the measurements performed will be presented. First conclusions from the available data are also discussed. | ||
| DOI • | reference for this paper ※ DOI:10.18429/JACoW-IPAC2016-WEPMW032 | |
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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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| 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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