IPAC2016 - List of Authors (Redaelli, S.)

Paper	Title	Page
MOPOR008	Beam Induced RF Heating in LHC in 2015	602
	B. Salvant, O. Aberle, M. Albert, R. Alemany-Fernandez, G. Arduini, J. Baechler, M.J. Barnes, P. Baudrenghien, O.E. Berrig, N. Biancacci, G. Bregliozzi, J.V. Campelo, F. Carra, F. Caspers, P. Chiggiato, A. Danisi, H.A. Day, M. Deile, D. Druzhkin, J.F. Esteban Müller, S. Jakobsen, J. Kuczerowski, A. Lechner, R. Losito, A. Masi, N. Minafra, E. Métral, A.A. Nosych, A. Perillo Marcone, D. Perini, S. Redaelli, F. Roncarolo, G. Rumolo, E.N. Shaposhnikova, J.A. Uythoven, C. Vollinger, A.J. Välimaa, N. Wang, M. Wendt, J. Wenninger, C. Zannini CERN, Geneva, Switzerland M. Bozzo INFN Genova, Genova, Italy J.F. Esteban Müller EPFL, Lausanne, Switzerland N. Wang IHEP, Beijing, People's Republic of China
	Following the recurrent beam induced RF issues that perturbed LHC operation during LHC Run 1, a series of actions were put in place to minimize the risk that similar issues would occur in LHC Run 2: longitudinal impedance reduction campaign and/or improvement of cooling for equipment that were problematic or at the limit during Run 1, stringent constraints enforced on new equipment that would be installed in the machine, tests to control the bunch length and longitudinal distribution, additional monitoring of temperature, new monitoring tools and warning chains. This contribution reports the outcome of these actions, both successes as well as shortcomings, and details the lessons learnt for the future runs.
DOI •	reference for this paper ※ DOI:10.18429/JACoW-IPAC2016-MOPOR008
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TUPMW006	Power Deposition in LHC Magnets Due to Bound-Free Pair Production in the Experimental Insertions	1418
	C. Bahamonde Castro, B. Auchmann, M.I. Besana, K. Brodzinski, R. Bruce, F. Cerutti, J.M. Jowett, A. Lechner, T. Mertens, V. Parma, S. Redaelli, M. Schaumann, N.V. Shetty, E. Skordis, G.E. Steele, R. van Weelderen CERN, Geneva, Switzerland
	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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TUPMW014	Improved Aperture Measurements at the LHC and Results from their Application in 2015	1446
	P.D. Hermes, R. Bruce, M. Fiascaris, H. Garcia, M. Giovannozzi, A. Mereghetti, D. Mirarchi, E. Quaranta, S. Redaelli, B. Salvachua, G. Valentino CERN, Geneva, Switzerland R. Kwee-Hinzmann Royal Holloway, University of London, Surrey, United Kingdom E. Quaranta Politecnico/Milano, Milano, Italy
	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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TUPMW021	Roman Pot Insertions in High-Intensity Beams for the CT-PPS Project at LHC	1473
	M. Deile, R. Bruce, A. Mereghetti, D. Mirarchi, S. Redaelli, B. Salvachua, B. Salvant, G. Valentino CERN, Geneva, Switzerland
	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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TUPMW027	The 2015 Heavy-Ion Run of the LHC	1493
	J.M. Jowett, R. Alemany-Fernandez, R. Bruce, M. Giovannozzi, P.D. Hermes, W. Höfle, M. Lamont, T. Mertens, S. Redaelli, M. Schaumann, J.A. Uythoven, J. Wenninger CERN, Geneva, Switzerland
	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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TUPMW031	Combined Ramp and Squeeze to 6.5 TeV in the LHC	1509
	M. Solfaroli Camillocci, S. Redaelli, R. Tomás, J. Wenninger CERN, Geneva, Switzerland
	The cycle of the LHC is composed of an energy ramp followed by a betatron squeeze, needed to reduce the beta- star value in the interaction points. Since Run 1, studies have been carried out to investigate the feasibility of combining the two operations, thus considerably reducing the duration of the operational cycle. In Run 2, the LHC is operating at the energy of 6.5 TeV that requires a much longer cycle than that of Run 1. Therefore, the performance gains from a Combined Ramp and Squeeze (CRS) is more interesting. Merging the energy ramp and the betatron squeeze could result in a gain of several minutes for each LHC cycle. With increasing maturity of LHC operation, it is now possible to envisage more complex beam manipulations; this paper describes the first machine experiment with beam, aiming at validating the combination of ramp and squeeze, which was performed in 2015, during a machine development phase. The operation experience with the LHC run at 2.51 TeV, when CRS down to 4 meters was deployed and a the first results of 2016 run are also reviewed.
DOI •	reference for this paper ※ DOI:10.18429/JACoW-IPAC2016-TUPMW031
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WEOCA01	Operation of the LHC with Protons at High Luminosity and High Energy	2066
	G. Papotti, M. Albert, R. Alemany-Fernandez, G.E. Crockford, K. Fuchsberger, R. Giachino, M. Giovannozzi, G.H. Hemelsoet, W. Höfle, D. Jacquet, M. Lamont, D. Nisbet, L. Normann, M. Pojer, L. Ponce, S. Redaelli, B. Salvachua, M. Solfaroli Camillocci, R. Suykerbuyk, J.A. Uythoven, J. Wenninger CERN, Geneva, Switzerland
	In 2015 the Large Hadron Collider (LHC) entered the first year in its second long Run, after a 2-year shutdown that prepared it for high energy. The first two months of beam operation were dedicated to setting up the nominal cycle for proton-proton operation at 6.5 TeV/beam, and culminated with the first physics with 3 nominal bunches/ring at 13 TeV CoM on 3 June. The year continued with a stepwise intensity ramp up that allowed reaching 2244 bunches/ring for a peak luminosity of ~5·10³³ cm^-2s⁻¹ and a total of just above 4 fb-1 delivered to the high luminosity experiments. Beam operation was shaped by the high intensity effects, e.g. electron cloud and macroparticle-induced fast losses (UFOs), which on a few occasions caused the first beam induced quenches at high energy. This paper describes the operational experience with high intensity and high energy at the LHC, together with the issues that had to be tackled along the way.
	Slides WEOCA01 [4.013 MB]
DOI •	reference for this paper ※ DOI:10.18429/JACoW-IPAC2016-WEOCA01
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WEPMW006	First Design of a Proton Collimation System for 50 TeV FCC-hh	2423
	M. Fiascaris, R. Bruce, D. Mirarchi, S. Redaelli CERN, Geneva, Switzerland
	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
	B. Salvachua, P. Baudrenghien, R. Bruce, H. Garcia, P.D. Hermes, S. Jackson, M. Jaussi, A. Mereghetti, D. Mirarchi, S. Redaelli, H. Timko, G. Valentino, A. Valloni CERN, Geneva, Switzerland R. Kwee-Hinzmann Royal Holloway, University of London, Surrey, United Kingdom
	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
	J.F. Wagner Goethe Universität Frankfurt, Frankfurt am Main, Germany R. Bruce, H. Garcia Morales, W. Höfle, G. Kotzian, R. Kwee-Hinzmann, A. Langner, A. Mereghetti, E. Quaranta, S. Redaelli, A. Rossi, B. Salvachua, R. Tomás, G. Valentino, D. Valuch, J.F. Wagner CERN, Geneva, Switzerland G. Stancari Fermilab, Batavia, Illinois, USA
	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.
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
	P.D. Hermes, R. Bruce, F. Cerutti, A. Ferrari, J.M. Jowett, A. Lechner, A. Mereghetti, D. Mirarchi, P.G. Ortega, S. Redaelli, B. Salvachua, E. Skordis, G. Valentino, V. Vlachoudis CERN, Geneva, Switzerland
	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.
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
	D. Mirarchi, A. Bertarelli, R. Bruce, F. Cerutti, P.D. Hermes, A. Lechner, A. Mereghetti, E. Quaranta, S. Redaelli CERN, Geneva, Switzerland R.B. Appleby UMAN, Manchester, United Kingdom H. Garcia Morales, R. Kwee-Hinzmann Royal Holloway, University of London, Surrey, United Kingdom
	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
	E. Quaranta, A. Bertarelli, N. Biancacci, R. Bruce, F. Carra, E. Métral, S. Redaelli, A. Rossi, B. Salvant CERN, Geneva, Switzerland F. Carra Politecnico di Torino, Torino, Italy
	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.
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WEPMW032	Radiation-induced Effects on LHC Collimator Materials under Extreme Beam Conditions	2502
	E. Quaranta, A. Bertarelli, F. Carra, P.D. Hermes, S. Redaelli, A. Rossi CERN, Geneva, Switzerland K. Bunk Goethe Universität Frankfurt, Frankfurt am Main, Germany F. Carra Politecnico di Torino, Torino, Italy J. Guardia Valenzuela Universidad de Zaragoza, Zaragoza, Spain P.D. Hermes Westfaelische Wilhelms-Universität Muenster, Muenster, Germany C.L. Hubert, M. Tomut GSI, Darmstadt, Germany P. Nocera Università di Roma I La Sapienza, Roma, Italy C. Porth TU Darmstadt, Darmstadt, Germany N. Simos BNL, Upton, Long Island, New York, USA
	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.
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WEPMW033	Validation of Simulation Tools for Fast Beam Failure Studies in the LHC	2506
	E. Quaranta, C. Bracco, R. Bruce, S. Redaelli CERN, Geneva, Switzerland
	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
	G. Valentino, G. Baud, R. Bruce, M. Gąsior, J. Olexa, S. Redaelli, A. Valloni, J. Wenninger CERN, Geneva, Switzerland
	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
	A. Valloni, R. Bruce, A. Mereghetti, E. Quaranta, S. Redaelli CERN, Geneva, Switzerland R.B. Appleby UMAN, Manchester, United Kingdom J. Molson LAL, Orsay, France H. Rafique University of Huddersfield, Huddersfield, United Kingdom
	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.
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WEPMW037	MERLIN Simulations of the LHC Collimation System with 6.5 TeV Beams	2518
	A. Valloni Rome University La Sapienza, Roma, Italy R.B. Appleby, S.C. Tygier UMAN, Manchester, United Kingdom R. Bruce, A. Mereghetti, S. Redaelli CERN, Geneva, Switzerland J. Molson LAL, Orsay, France H. Rafique University of Huddersfield, Huddersfield, United Kingdom
	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.
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WEPOY047	LHC Collimation and Energy Deposition Studies Using Beam Delivery Simulation (BDSIM)	3101
	L.J. Nevay, S.T. Boogert, S.M. Gibson, R. Kwee-Hinzmann JAI, Egham, Surrey, United Kingdom R. Bruce, H. Garcia, S. Redaelli CERN, Geneva, Switzerland
	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.
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Paper

Title

Page

Beam Induced RF Heating in LHC in 2015

602

B. Salvant, O. Aberle, M. Albert, R. Alemany-Fernandez, G. Arduini, J. Baechler, M.J. Barnes, P. Baudrenghien, O.E. Berrig, N. Biancacci, G. Bregliozzi, J.V. Campelo, F. Carra, F. Caspers, P. Chiggiato, A. Danisi, H.A. Day, M. Deile, D. Druzhkin, J.F. Esteban Müller, S. Jakobsen, J. Kuczerowski, A. Lechner, R. Losito, A. Masi, N. Minafra, E. Métral, A.A. Nosych, A. Perillo Marcone, D. Perini, S. Redaelli, F. Roncarolo, G. Rumolo, E.N. Shaposhnikova, J.A. Uythoven, C. Vollinger, A.J. Välimaa, N. Wang, M. Wendt, J. Wenninger, C. Zannini
CERN, Geneva, Switzerland
M. Bozzo
INFN Genova, Genova, Italy
J.F. Esteban Müller
EPFL, Lausanne, Switzerland
N. Wang
IHEP, Beijing, People's Republic of China

Following the recurrent beam induced RF issues that perturbed LHC operation during LHC Run 1, a series of actions were put in place to minimize the risk that similar issues would occur in LHC Run 2: longitudinal impedance reduction campaign and/or improvement of cooling for equipment that were problematic or at the limit during Run 1, stringent constraints enforced on new equipment that would be installed in the machine, tests to control the bunch length and longitudinal distribution, additional monitoring of temperature, new monitoring tools and warning chains. This contribution reports the outcome of these actions, both successes as well as shortcomings, and details the lessons learnt for the future runs.

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reference for this paper ※ DOI:10.18429/JACoW-IPAC2016-MOPOR008

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TUPMW006

Power Deposition in LHC Magnets Due to Bound-Free Pair Production in the Experimental Insertions

1418

C. Bahamonde Castro, B. Auchmann, M.I. Besana, K. Brodzinski, R. Bruce, F. Cerutti, J.M. Jowett, A. Lechner, T. Mertens, V. Parma, S. Redaelli, M. Schaumann, N.V. Shetty, E. Skordis, G.E. Steele, R. van Weelderen
CERN, Geneva, Switzerland

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.

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reference for this paper ※ DOI:10.18429/JACoW-IPAC2016-TUPMW006

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TUPMW014

Improved Aperture Measurements at the LHC and Results from their Application in 2015

1446

P.D. Hermes, R. Bruce, M. Fiascaris, H. Garcia, M. Giovannozzi, A. Mereghetti, D. Mirarchi, E. Quaranta, S. Redaelli, B. Salvachua, G. Valentino
CERN, Geneva, Switzerland
R. Kwee-Hinzmann
Royal Holloway, University of London, Surrey, United Kingdom
E. Quaranta
Politecnico/Milano, Milano, Italy

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.

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TUPMW021

Roman Pot Insertions in High-Intensity Beams for the CT-PPS Project at LHC

1473

M. Deile, R. Bruce, A. Mereghetti, D. Mirarchi, S. Redaelli, B. Salvachua, B. Salvant, G. Valentino
CERN, Geneva, Switzerland

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.

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TUPMW027

The 2015 Heavy-Ion Run of the LHC

1493

J.M. Jowett, R. Alemany-Fernandez, R. Bruce, M. Giovannozzi, P.D. Hermes, W. Höfle, M. Lamont, T. Mertens, S. Redaelli, M. Schaumann, J.A. Uythoven, J. Wenninger
CERN, Geneva, Switzerland

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.

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TUPMW031

Combined Ramp and Squeeze to 6.5 TeV in the LHC

1509

M. Solfaroli Camillocci, S. Redaelli, R. Tomás, J. Wenninger
CERN, Geneva, Switzerland

The cycle of the LHC is composed of an energy ramp followed by a betatron squeeze, needed to reduce the beta- star value in the interaction points. Since Run 1, studies have been carried out to investigate the feasibility of combining the two operations, thus considerably reducing the duration of the operational cycle. In Run 2, the LHC is operating at the energy of 6.5 TeV that requires a much longer cycle than that of Run 1. Therefore, the performance gains from a Combined Ramp and Squeeze (CRS) is more interesting. Merging the energy ramp and the betatron squeeze could result in a gain of several minutes for each LHC cycle. With increasing maturity of LHC operation, it is now possible to envisage more complex beam manipulations; this paper describes the first machine experiment with beam, aiming at validating the combination of ramp and squeeze, which was performed in 2015, during a machine development phase. The operation experience with the LHC run at 2.51 TeV, when CRS down to 4 meters was deployed and a the first results of 2016 run are also reviewed.

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WEOCA01

Operation of the LHC with Protons at High Luminosity and High Energy

2066

G. Papotti, M. Albert, R. Alemany-Fernandez, G.E. Crockford, K. Fuchsberger, R. Giachino, M. Giovannozzi, G.H. Hemelsoet, W. Höfle, D. Jacquet, M. Lamont, D. Nisbet, L. Normann, M. Pojer, L. Ponce, S. Redaelli, B. Salvachua, M. Solfaroli Camillocci, R. Suykerbuyk, J.A. Uythoven, J. Wenninger
CERN, Geneva, Switzerland

In 2015 the Large Hadron Collider (LHC) entered the first year in its second long Run, after a 2-year shutdown that prepared it for high energy. The first two months of beam operation were dedicated to setting up the nominal cycle for proton-proton operation at 6.5 TeV/beam, and culminated with the first physics with 3 nominal bunches/ring at 13 TeV CoM on 3 June. The year continued with a stepwise intensity ramp up that allowed reaching 2244 bunches/ring for a peak luminosity of ~5·10³³ cm^-2s⁻¹ and a total of just above 4 fb-1 delivered to the high luminosity experiments. Beam operation was shaped by the high intensity effects, e.g. electron cloud and macroparticle-induced fast losses (UFOs), which on a few occasions caused the first beam induced quenches at high energy. This paper describes the operational experience with high intensity and high energy at the LHC, together with the issues that had to be tackled along the way.

Slides WEOCA01 [4.013 MB]

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WEPMW006

First Design of a Proton Collimation System for 50 TeV FCC-hh

2423

M. Fiascaris, R. Bruce, D. Mirarchi, S. Redaelli
CERN, Geneva, Switzerland

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.

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WEPMW007

Validation of Off-momentum Cleaning Performance of the LHC Collimation System

2427

B. Salvachua, P. Baudrenghien, R. Bruce, H. Garcia, P.D. Hermes, S. Jackson, M. Jaussi, A. Mereghetti, D. Mirarchi, S. Redaelli, H. Timko, G. Valentino, A. Valloni
CERN, Geneva, Switzerland
R. Kwee-Hinzmann
Royal Holloway, University of London, Surrey, United Kingdom

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.

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WEPMW028

First Attempts at using Active Halo Control at the LHC

2486

J.F. Wagner
Goethe Universität Frankfurt, Frankfurt am Main, Germany
R. Bruce, H. Garcia Morales, W. Höfle, G. Kotzian, R. Kwee-Hinzmann, A. Langner, A. Mereghetti, E. Quaranta, S. Redaelli, A. Rossi, B. Salvachua, R. Tomás, G. Valentino, D. Valuch, J.F. Wagner
CERN, Geneva, Switzerland
G. Stancari
Fermilab, Batavia, Illinois, USA

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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WEPMW029

Simulation of Heavy-Ion Beam Losses with the SixTrack-FLUKA Active Coupling

2490

SUPSS008

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P.D. Hermes, R. Bruce, F. Cerutti, A. Ferrari, J.M. Jowett, A. Lechner, A. Mereghetti, D. Mirarchi, P.G. Ortega, S. Redaelli, B. Salvachua, E. Skordis, G. Valentino, V. Vlachoudis
CERN, Geneva, Switzerland

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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WEPMW030

Cleaning Performance of the Collimation System of the High Luminosity Large Hadron Collider

2494

D. Mirarchi, A. Bertarelli, R. Bruce, F. Cerutti, P.D. Hermes, A. Lechner, A. Mereghetti, E. Quaranta, S. Redaelli
CERN, Geneva, Switzerland
R.B. Appleby
UMAN, Manchester, United Kingdom
H. Garcia Morales, R. Kwee-Hinzmann
Royal Holloway, University of London, Surrey, United Kingdom

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.

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WEPMW031

Towards Optimum Material Choices for the HL-LHC Collimator Upgrade

2498

E. Quaranta, A. Bertarelli, N. Biancacci, R. Bruce, F. Carra, E. Métral, S. Redaelli, A. Rossi, B. Salvant
CERN, Geneva, Switzerland
F. Carra
Politecnico di Torino, Torino, Italy

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.

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WEPMW032

Radiation-induced Effects on LHC Collimator Materials under Extreme Beam Conditions

2502

E. Quaranta, A. Bertarelli, F. Carra, P.D. Hermes, S. Redaelli, A. Rossi
CERN, Geneva, Switzerland
K. Bunk
Goethe Universität Frankfurt, Frankfurt am Main, Germany
F. Carra
Politecnico di Torino, Torino, Italy
J. Guardia Valenzuela
Universidad de Zaragoza, Zaragoza, Spain
P.D. Hermes
Westfaelische Wilhelms-Universität Muenster, Muenster, Germany
C.L. Hubert, M. Tomut
GSI, Darmstadt, Germany
P. Nocera
Università di Roma I La Sapienza, Roma, Italy
C. Porth
TU Darmstadt, Darmstadt, Germany
N. Simos
BNL, Upton, Long Island, New York, USA

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.

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WEPMW033

Validation of Simulation Tools for Fast Beam Failure Studies in the LHC

2506

E. Quaranta, C. Bracco, R. Bruce, S. Redaelli
CERN, Geneva, Switzerland

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.

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WEPMW034

First Operational Experience with Embedded Collimator BPMs in the LHC

2510

G. Valentino, G. Baud, R. Bruce, M. Gąsior, J. Olexa, S. Redaelli, A. Valloni, J. Wenninger
CERN, Geneva, Switzerland

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.

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WEPMW036

MERLIN Cleaning Studies with Advanced Collimator Materials for HL-LHC

2514

A. Valloni, R. Bruce, A. Mereghetti, E. Quaranta, S. Redaelli
CERN, Geneva, Switzerland
R.B. Appleby
UMAN, Manchester, United Kingdom
J. Molson
LAL, Orsay, France
H. Rafique
University of Huddersfield, Huddersfield, United Kingdom

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.

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WEPMW037

MERLIN Simulations of the LHC Collimation System with 6.5 TeV Beams

2518

A. Valloni
Rome University La Sapienza, Roma, Italy
R.B. Appleby, S.C. Tygier
UMAN, Manchester, United Kingdom
R. Bruce, A. Mereghetti, S. Redaelli
CERN, Geneva, Switzerland
J. Molson
LAL, Orsay, France
H. Rafique
University of Huddersfield, Huddersfield, United Kingdom

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.

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WEPOY047

LHC Collimation and Energy Deposition Studies Using Beam Delivery Simulation (BDSIM)

3101

L.J. Nevay, S.T. Boogert, S.M. Gibson, R. Kwee-Hinzmann
JAI, Egham, Surrey, United Kingdom
R. Bruce, H. Garcia, S. Redaelli
CERN, Geneva, Switzerland

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.

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