Author: Biancacci, N.
Paper Title Page
MOPMF053 Observations, Analysis and Mitigation of Recurrent LHC Beam Dumps Caused by Fast Losses in Arc Half-Cell 16L2 228
 
  • J.M. Jimenez, D. Amorim, S. A. Antipov, G. Arduini, A. Bertarelli, N. Biancacci, B. Bradu, E. Bravin, G. Bregliozzi, K. Brodzinski, R. Bruce, X. Buffat, L.R. Carver, P. Chiggiato, S.D. Claudet, P. Collier, R. Garcia Alia, M. Giovannozzi, L. K. Grob, E.B. Holzer, W. Höfle, G. Iadarola, G. Kotzian, A. Lechner, T.E. Levens, B. Lindstrom, T. Medvedeva, A. Milanese, D. Mirarchi, E. Métral, D. Perini, S. Redaelli, G. Rumolo, B. Salvant, R. Schmidt, M. Valette, D. Valuch, J. Wenninger, D. Wollmann, C. Yin Vallgren, C. Zamantzas, M. Zerlauth
    CERN, Geneva, Switzerland
  • D. Amorim
    Université Grenoble Alpes, Grenoble, France
  • A.A. Gorzawski
    University of Manchester, Manchester, United Kingdom
  • L. Mether
    EPFL, Lausanne, Switzerland
 
  Recurrent beam dumps significantly perturbed the operation of the CERN LHC in the summer months of 2017, especially in August. These unexpected beam dumps were triggered by fast beam losses that built up in the cryogenic beam vacuum at the half-cell 16 left of LHC-IP2 and were detected either at that location but mainly in the collimation insertions. This contribution details the experimental observables (beam losses, coherent instabilities, heat load to cryogenic system, vacuum signals), the extent of the understanding of the beam loss and instability mechanisms and the mitigation steps and new settings that allowed recovering the luminosity performance of the LHC for the rest of the Run.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-MOPMF053  
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TUPAF020 Performance of the CERN Low Energy Ion Ring (LEIR) with Xenon beams 705
 
  • R. Alemany-Fernández, S.C.P. Albright, O. Andujar, M.E. Angoletta, J. Axensalva, H. Bartosik, G. Baud, N. Biancacci, M. Bozzolan, S. Cettour Cave, K. Cornelis, J. Dalla-Costa, M. Delrieux, A. Dworak, A. Findlay, F. Follin, A. Frassier, M. Gabriel, A. Guerrero, M. Haase, S. Hirlaender, S. Jensen, V. Kain, L.V. Kolbeck, Y. Le Borgne, D. Manglunki, O. Marqversen, S. Massot, D. Moreno Garcia, D.J.P. Nicosia, S. Pasinelli, L. Pereira, D. Perez, A. Rey, J.P. Ridewood, F. Roncarolo, Á. Saá Hernández, R. Scrivens, O.G. Sveen, G. Tranquille, E. Veyrunes
    CERN, Geneva, Switzerland
 
  In 2017 the CERN Low Energy Ion Ring demonstrated once more the feasibility of injecting, accumulating, cooling and accelerating a new nuclei, 129Xe39 . The operation of this new ion species started at the beginning of March with the start up of the xenon ion source and the Linac3. Ten weeks later the beam arrived to the Low Energy Ion Ring (LEIR) triggering the start of several weeks of beam commissioning in view of providing the injector complex with Xenon beams for different experiments and a series of machine development experiments in LEIR. Two types of beams were setup, the so called EARLY beam, with a single injection into LEIR from Linac3, and the NOMINAL beam with up to seven injections. 2017 was as well an interesting year for LEIR because several improvements in the control system of the accelerator and in the beam instrumentation were done in view of increasing the machine reliability. This paper summarises the beam commissioning phase and all the improvements carried out during 2017.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-TUPAF020  
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TUPAF024 Impedance and Instability Studies in LEIR with Xenon 720
 
  • N. Biancacci, H. Bartosik, M. Gąsior, S. Hirlaender, V. Kain, T.E. Levens, E. Métral
    CERN, Geneva, Switzerland
  • M. Migliorati
    Rome University La Sapienza, Roma, Italy
 
  In 2017, the LEIR accelerator has been operated with Xe39+ beam for fixed target experiments in the SPS North Area. The different ion species, with respect to the usually operated Pb54+, allowed for additional comparative measurements of tune shift versus intensity at injection energy both in coasting and bunched beams. The fast transverse instability observed for high accumulated intensities has been as well characterized and additional observations relevant to impedance have been collected from longitudinal Schottky signal and BTF measurements. The results of these measurements are summarised and compared to the currently developed machine impedance model.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-TUPAF024  
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TUPAF034 LEIR Injection Efficiency Studies as a Function of the Beam Energy Distribution from Linac3 758
 
  • S. Hirlaender, R. Alemany-Fernández, H. Bartosik, G. Bellodi, N. Biancacci, V. Kain, R. Scrivens
    CERN, Geneva, Switzerland
 
  High intensities in the CERN Low Energy Ion Ring (LEIR) are achieved using multi-turn injections from the pre-accelerator Linac3 combined with simultaneous stacking in momentum and transverse phase spaces. Up to seven consecutive 200 μs long, 200 ms spaced pulses are injected from Linac3 into LEIR by stacking each of them into the six-dimensional phase-space over 70 turns. An inclined septum magnet allows proper filling of the transverse phase-space plane, while longitudinal stacking requires momentum variation achieved by a shift of mean momentum over time provided by phase shifting a combination of 2 RF cavities at the exit of Linac3. The achievable maximum accumulated intensity depends strongly on the longitudinal beam quality of the injected beam. The longitudinal Schottky signal is used to measure the received energy distribution of the circulating beam which is then correlated with the obtained injection efficiency. This paper presents the experimental studies to understand and further improve the injection reliability and the longitudinal stacking.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-TUPAF034  
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TUPAF036 Studies of the Injection and Cooling Efficiency in LEIR Using the Longitudinal Schottky Spectrum 765
 
  • S. Hirlaender, R. Alemany-Fernández, H. Bartosik, N. Biancacci, V. Kain
    CERN, Geneva, Switzerland
 
  The CERN Low Energy Ion Ring (LEIR) has two main operational beams with their associated cycles, the so-called EARLY and the NOMINAL beam. The EARLY beam consists of a single injected pulse from the LINAC3 accelerator, whereas seven consecutive injections are accumulated, and electron cooled for the NOMINAL beam. In both cases, the longitudinal Schottky monitor allows assessing the longitudinal particle distribution during the cooling process on the injection plateau. A method has been established to analyze the Schottky signal, reconstruct the initial particle momentum distribution and derive relevant parameters such as the cooling time, energy off-set of injected and stacked beam or the momentum distribution of the lost beam. The variations of the obtained parameters and the impact on the LEIR performance will be addressed.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-TUPAF036  
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TUPAF039 Electron Cooling Simulation and Experimental Benchmarks at LEIR 776
 
  • A. Latina, H. Bartosik, N. Biancacci, R. Corsini, D. Gamba, S. Hirlaender, A. Huschauer
    CERN, Geneva, Switzerland
 
  A fast and accurate simulation of Electron Cooling has recently been implemented in the tracking code RF-Track. The implementation, which is based on a "hybrid kinetic" model, enables the simulation of a large variety of realistic scenarios, including imperfections such as gradients in the electron density, misalignments of electrons / ions / solenoidal fields, both in the static and in the dynamic regimes. Benchmarks of the simulations against measurements performed at LEIR, using Lead and Xenon ions, are presented.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-TUPAF039  
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WEYGBD3 The CERN Gamma Factory Initiative: An Ultra-High Intensity Gamma Source 1780
 
  • M.W. Krasny
    LPNHE, Paris, France
  • R. Alemany-Fernández, H. Bartosik, N. Biancacci, P. Czodrowski, B. Goddard, S. Hirlaender, J.M. Jowett, R. Kersevan, M. Kowalska, M.W. Krasny, M. Lamont, D. Manglunki, A.V. Petrenko, M. Schaumann, C. Yin Vallgren, F. Zimmermann
    CERN, Geneva, Switzerland
  • P.S. Antsifarov
    Institute of Spectroscopy, Russian Academy of Science, Troitsk, Moscow, Russia
  • A. Apyan
    ANSL, Yerevan, Armenia
  • E.G. Bessonov
    LPI, Moscow, Russia
  • J. Bieron, K. Dzierzega, W. Placzek, S. Pustelny
    Marian Smoluchowski Institute of Physics, Jagiellonian University, Kraków, Poland
  • D. Budker
    Johannes Gutenberg University Mainz, Institut für Physik, Mainz, Germany
  • K. Cassou, I. Chaikovska, R. Chehab, K. Dupraz, A. Martens, Z.F. Zomer
    LAL, Orsay, France
  • F. Castelli
    Università degli Studi di Milano, Milano, Italy
  • C. Curatolo, L. Serafini
    Istituto Nazionale di Fisica Nucleare, Milano, Italy
  • K. Kroeger
    FSU Jena, Jena, Germany
  • V. Petrillo
    Universita' degli Studi di Milano & INFN, Milano, Italy
  • V.P. Shevelko
    LPI RAS, Moscow, Russia
  • T. Stöhlker
    HIJ, Jena, Germany
  • G. Weber
    IOQ, Jena, Germany
  • Y.K. Wu
    FEL/Duke University, Durham, North Carolina, USA
  • M.S. Zolotorev
    LBNL, Berkeley, California, USA
 
  This contribution discusses the possibility of broadening the present CERN research programme making use of a novel concept of light source. The proposed, Partially Stripped Ion beam driven, light source is the backbone of the Gamma Factory (GF) initiative. It could be realized at CERN by using the infrastructure of the already existing accelerators. It could push the intensity limits of the presently operating light-sources by up to 7 orders of magnitude, reaching fluxes of 1017 photons/s in the interesting gamma-ray energy domain between 1 MeV and 400 MeV. The GF light-source cannot be replaced, in this energy domain, by a FEL source as long as the multi TeV electron beams are not available. Its intensity is beyond the reach of the Inverse Compton Scattering sources. The unprecedented-intensity, energy-tuned gamma beams, together with the gamma-beams-driven secondary beams of polarized leptons, neutrinos, neutrons and radioactive ions are the basic research tools of the proposed Gamma Factory. A broad spectrum of new opportunities, in a vast domain of uncharted fundamental and applied physics territories, could be opened by the Gamma Factory research programme.  
slides icon Slides WEYGBD3 [7.537 MB]  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-WEYGBD3  
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WEYGBE4 Low-Impedance Collimators for HL-LHC 1794
 
  • S. A. Antipov, N. Biancacci, R. Bruce, A. Mereghetti, D. Mirarchi, E. Métral, S. Redaelli, B. Salvant
    CERN, Geneva, Switzerland
  • D. Amorim
    Université Grenoble Alpes, Grenoble, France
 
  The High-Luminosity upgrade of the Large Hadron Collider (HL-LHC) will double its beam intensity for the needs of High Energy Physics frontier. This increase requires a reduction of the machine's impedance to ensure the coherent stability of the beams until they are put in collision. A major part of the impedance is the resistive wall contribution of the collimators. To reduce this contribution several coating options have been proposed. We have studied numerically the effect of the novel coatings on the beam stability. The results show that a decrease of up to 30% of the machine impedance and a reduction of up to 120 A in the stabilizing octupole current threshold can be achieved by coating the secondary collimators with Molybdenum. Half of that improvement can be obtained by coating the jaws of a subset of four collimators identified as the highest contributors to machine impedance. The installation of this subset of low-impedance collimators is planned for the Long Shutdown 2 in 2019-2020.  
slides icon Slides WEYGBE4 [5.724 MB]  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-WEYGBE4  
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THPAF035 Single-Collimator Tune Shift Measurement of the Three-Stripe Collimator at the LHC 3036
 
  • S. A. Antipov
    University of Chicago, Chicago, Illinois, USA
  • D. Amorim, N. Biancacci, L.R. Carver, G. Mazzacano, A. Mereghetti, E. Métral, S. Redaelli, B. Salvant, D. Valuch
    CERN, Geneva, Switzerland
 
  Several options of low resistivity coating have been proposed for the collimator upgrade of the Large Hadron Collider. In order to study their effect on the beam dynamics a special collimator has been built and installed in the machine. Its jaws are coated with three different materials and can be moved transversely to selectively expose the beam to the chosen coating. We have measured the resistive wall tune shifts of each coating material and compared them with that of a standard Carbon Fibre Composite (CFC) collimator jaw. A resolution of the tune shift of the order of 10-5 has been achieved in the measurement. The results show a significant reduction of the resistive wall tune shift with novel materials. The largest improvement is obtained with a 5 μm Molybdenum coating of a Molybdenum-Graphite jaw. The observed tune shifts show a good agreement with the impedance model and the bench impedance and resistivity measurements. Obtained results can be used to further improve the precision of the impedance model.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-THPAF035  
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THPAF036 Longitudinal and Quadrupolar Coupling Impedance of an Elliptical Vacuum Chamber With Finite Conductivity in Terms of Mathieu Functions 3040
 
  • M. Migliorati, L. Palumbo
    Sapienza University of Rome, Rome, Italy
  • N. Biancacci
    CERN, Geneva, Switzerland
  • M. Migliorati, L. Palumbo
    INFN-Roma1, Rome, Italy
  • V.G. Vaccaro
    Naples University Federico II and INFN, Napoli, Italy
 
  Funding: Work supported by the CERN PS-LIU project
The resistive wall impedance of an elliptical vacuum chamber in the classical regime with infinite thickness is known analytically for ultra-relativistic beams by means of the Yokoya form factors. Starting from the longitudinal electric field of a point charge moving at arbitrary speed in an elliptical vacuum chamber, which we express in terms of Mathieu functions, in this paper we take into account the finite conductivity of the beam pipe walls and evaluate the longitudinal and quadrupolar impedance for any beam velocity. We also obtain that the quadrupolar impedance of a circular pipe is different from zero, approaching zero only for ultra-relativistic particles. Even if some of the results, in particular in the ultra-relativistic limit, are already known and expressed in terms of form factors, this approach is the first step towards the calculation of the general problem of a multi-layer vacuum chamber with different conductivities and of elliptic cross section.
 
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-THPAF036  
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THPAF048 Destabilising Effect of the LHC Transverse Damper 3076
 
  • E. Métral, D. Amorim, S. A. Antipov, N. Biancacci, X. Buffat, K.S.B. Li
    CERN, Geneva, Switzerland
 
  Three questions motivated this study for the CERN Large Hadron Collider in terms of beam stability: (i) why a chromaticity close to zero seemed more critical than predicted during Run 1 (in 2011 and 2012) and during Run 2 (in 2015)?; (ii) why some past simulations with a chromaticity close to zero revealed a more critical situation with the transverse damper than without?; (iii) what should be the minimum operational chromaticity in the future in the LHC and High-Luminosity LHC? A new Vlasov solver (called GALACTIC) was developed to shed light on the destabilising mechanism of the transverse damper, which is a potential contributor to explain the LHC observation. Due to the features, which are discussed in this paper, the name 'ISR (for Imaginary tune Split and Repulsion) instability' is suggested for this new kind of single-bunch instability with zero chromaticity.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-THPAF048  
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THPAF055 Space Charge Studies on LEIR 3095
 
  • Á. Saá Hernández, H. Bartosik, N. Biancacci, S. Hirlaender, A. Huschauer, D. Moreno Garcia
    CERN, Geneva, Switzerland
 
  The performance of the CERN Low Energy Ion Ring with electron cooled ion beams is presently limited by losses occurring once the beam has been captured in the RF buckets. An intense machine study program was started by the end of 2015 to mitigate the losses and improve the performance of the accelerator. The measurements pointed to the interplay of direct space charge forces and excited betatron resonances as the most plausible driving mechanism of these losses. In this paper, we present the systematic space-charge measurements performed in 2017 and compare them to space-charge tracking simulations based on an adaptive frozen potential.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-THPAF055  
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THPAF057 Instability Observations in the Large Hadron Collider During Run 2 3099
 
  • L.R. Carver, D. Amorim, S. A. Antipov, N. Biancacci, X. Buffat, G. Iadarola, K.S.B. Li, E.H. Maclean, L. Mether, E. Métral, B. Salvant, M. Schenk
    CERN, Geneva, Switzerland
  • L. Mether, M. Schenk
    EPFL, Lausanne, Switzerland
 
  Instabilities of many different types and characteristics have been observed in the LHC during Run 2. The origin of these instabilities come from a variety of stabilising and destabilising mechanisms. Efforts to understand these instabilities and prevent their occurrence has improved the performance of the LHC in all stages of the machine cycle. This paper aims to give an overview into some of the instability observations and details the operational steps to prevent them.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-THPAF057  
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THPAF058 Experimental Characterisation of a Fast Instability Linked to Losses in the 16L2 Cryogenic Half-Cell in the CERN LHC 3103
 
  • B. Salvant, S. A. Antipov, G. Arduini, N. Biancacci, X. Buffat, L.R. Carver, P. Collier, A.A. Gorzawski, W. Höfle, G. Iadarola, G. Kotzian, A. Lechner, T.E. Levens, D. Mirarchi, E. Métral, G. Rumolo, D. Valuch
    CERN, Geneva, Switzerland
  • L. Mether
    EPFL, Lausanne, Switzerland
 
  The operation during the summer months of the 2017 Run of the CERN LHC was plagued with fast beam losses that repeatedly occurred in the 16th arc half-cell at the left of IP2 as well as in the collimation insertion, leading to unwanted beam dumps. Transverse coherent oscillations were observed during this fast process. We detail here the experimental observations of coherent motion that al-lowed shedding light upon parts of the mechanism and identify the potential mitigations that were successfully implemented in the second half of the Run.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-THPAF058  
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THPMF015 Lifetime and Beam Losses Studies of Partially Strip Ions in the SPS (129Xe39+) 4070
 
  • S. Hirlaender, R. Alemany-Fernández, H. Bartosik, N. Biancacci, T. Bohl, S. Cettour Cave, K. Cornelis, B. Goddard, V. Kain, M.W. Krasny, M. Lamont, D. Manglunki, G. Papotti, M. Schaumann, F. Zimmermann
    CERN, Geneva, Switzerland
  • K. Kroeger
    FSU Jena, Jena, Germany
  • V.P. Shevelko
    LPI RAS, Moscow, Russia
  • T. Stöhlker, G. Weber
    IOQ, Jena, Germany
 
  The CERN multipurpose Gamma Factory proposal relies on using Partially Stripped Ion (PSI) beams, instead of electron beams, as the drivers of its light source. If such beams could be successfully stored in the LHC ring, fluxes of the order of 1017 photons/s, in the gamma-ray energy domain between 1 MeV and 400 MeV could be achieved. This energy domain is out of reach for the FEL-based light sources as long as the multi TeV electron beams are not available. The CERN Gamma Factory proposal has the potential of increasing by 7 orders of magnitude the intensity limits of the present Inverse Compton Scattering sources. In 2017 the CERN accelerator complex demonstrated its flexibility by producing a new, xenon, ion beam. The Gamma Factory study group, based on this achievement, requested special studies. Its aim was to inject and to accelerate, in the SPS, partially stripped xenon ions Xe39+ measure their life time, and determine the relative strength of the processes responsible for the PSI beam losses. This study, the results of which are presented in this contribution, was an initial step in view of the the future studies programmed for 2018 with lead PSI beams.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-THPMF015  
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