05 Beam Dynamics and EM Fields
D06 Coherent and Incoherent Instabilities - Measurements and Countermeasures
Paper Title Page
Studies of Horizontal Instabilities in the CERN-SPS  
  • M.S. Beck
    CERN, Geneva, Switzerland
  Student poster award talk  
slides icon Slides TUYGBD6 [1.227 MB]  
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TUPMK001 Removal of RF-Fingers at the Edges of the Injection Kickers 1485
  • T.F.G. Günzel, N. Ayala, F.F.B. Fernández, U. Iriso, M. Pont
    ALBA-CELLS Synchrotron, Cerdanyola del Vallès, Spain
  The ALBA storage ring injection kickers are equipped with RF-fingers to close a 2.5 mm gap between the ceramic tube and the metallic flange. After two distortion incidents that required the replacement of the fingers, their removal was decided. The decision could be supported by the observation that most of the additional impedance is created above the cut-off frequency of the beam pipe. This was later confirmed by a temperature decrease in that zone after the removal. Furthermore it was checked that the thresholds of the longitudinal coupled bunch instabilities of modes trapped around the resulting open gap are above the maximal applied beam current of 400 mA.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-TUPMK001  
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THPAF034 Studies of Horizontal Instabilities in the CERN SPS 3032
SUSPF091   use link to see paper's listing under its alternate paper code  
  • M.S. Beck, H. Bartosik, M. Carlà, K.S.B. Li, G. Rumolo, M. Schenk
    CERN, Geneva, Switzerland
  • U. van Rienen
    Rostock University, Faculty of Engineering, Rostock, Germany
  In the framework of the LHC Injectors Upgrade (LIU), beams with double intensity with respect to the present values will have to be successfully accelerated by the CERN Super Proton Synchrotron (SPS) and extracted towards the Large Hadron Collider (LHC). However, first experience running with intensity higher than the nominal LHC beam has shown that coherent instabilities in the horizontal plane may develop, becoming a potential intensity limitation for the future high intensity operation. To understand the mechanism of these instabilities, the PyHEADTAIL code has been used to check if the SPS impedance model reproduces the observations. The instability growth rates have been studied for different machine models and different chromaticity settings. In addition, the effect of other stabilizing methods, like the octupoles and the transverse damper, has also been investigated. Measurements are presented to benchmark the simulations.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-THPAF034  
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THPAF041 Uncontrolled Longitudinal Emittance Blow-Up during RF Manipulations in the CERN PS 3056
  • A. Lasheen, H. Damerau, G. Favia
    CERN, Geneva, Switzerland
  The CERN Proton Synchrotron (PS) determines the basic bunch spacing for the Large Hadron Collider (LHC) by means of rf manipulations. Several rf systems in a frequency range from 2.8 MHz to 200 MHz are available for beam acceleration and manipulations. Each of the six bunches injected from the PS Booster is split in several steps into 12 bunches spaced by 25 ns, yielding a batch of 72 bunches at transfer to the Super Proton Synchrotron (SPS). In the framework of the LHC Injector Upgrade (LIU) project the bunch intensity must be doubled. However, with most of the planned upgrades already in place this intensity has not yet been achieved due to collective effects. One of them is uncontrolled longitudinal emittance blow-up during the bunch splittings. In this contribution, measurements of the blow-up during the splitting process are presented and compared with particle simulations using the present PS impedance model. Beam-based measurements of the impedances of the rf cavities have been performed. They revealed that to reproduce the instability an additional impedance source is required in the PS impedance model.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-THPAF041  
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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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THPAK016 Measurement and Analysis of Synchrotron Tune Variation with Beam Current in BEPCII 3237
  • N. Wang, Z. Duan, G. Xu, H.S. Xu, C.H. Yu, Y. Zhang
    IHEP, Beijing, People's Republic of China
  Coherent synchrotron frequency shift is observed during machine studies in BEPCII (Beijing Electron Positron Collider Upgrade). The results show that the synchrotron frequency varies parabolically with the increase of the beam current. This phenomenon is supposed to be induced by the interaction of the beam with the fundamental mode of the accelerating cavity. In order to explain this phenomenon, a simple physical model is developed from the couple bunch instability theory. The analytical estimations based on the physical model show good agreement with the measurements.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-THPAK016  
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THPAK024 A new method to measure the Beta function in a Paul trap 3262
SUSPF080   use link to see paper's listing under its alternate paper code  
  • L. Martin, S.L. Sheehy
    JAI, Oxford, United Kingdom
  • K. Ito, H. Okamoto
    HU/AdSM, Higashi-Hiroshima, Japan
  • D.J. Kelliher
    STFC/RAL/ASTeC, Chilton, Didcot, Oxon, United Kingdom
  • S. Machida
    STFC/RAL/ISIS, Chilton, Didcot, Oxon, United Kingdom
  The Simulator of Particle Orbit Dynamics (S-POD) is a linear Paul trap at Hiroshima University, Japan, used to study beam physics. S-POD has so far been used to study resonances in high intensity beams, predominantly using a simple alternating gradient lattice configuration. Recently a similar apparatus, the Intense Beam Experiment (IBEX), has been constructed at the Rutherford Appleton Lab in the UK. To use either of these experiments to study beam dynamics in more complex lattice configurations in the future further diagnostic techniques must be developed for Paul traps. Here we describe a new method to measure the beta function and emittance at a given time in a Paul trap.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-THPAK024  
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THPAK029 Studies of the Micro-Bunching Instability in the Presence of a Damping Wiggler 3273
  • M. Brosi, A. Bernhard, J. Gethmann, B. Kehrer, A.-S. Müller, A.I. Papash, P. Schreiber, P. Schönfeldt, J.L. Steinmann
    KIT, Karlsruhe, Germany
  Funding: Funded by BMBF (grant: 05K16VKA) & Helmholtz (contract: VH-NG-320). Supported by the Helmholtz International Research School for Teratronics & Karlsruhe School of Elementary and Astroparticle Physics.
At the KIT storage ring KARA (KArlsruhe Research Accelerator), the momentum compaction factor can be reduced leading to natural bunch lengths in the ps range. Due to the high degree of longitudinal compression the micro-bunching instability arises. During this longitudinal instability the bunches emit bursts of intense coherent synchrotron radiation in the THz frequency range caused by the complex longitudinal dynamics. The temporal pattern of the emitted bursts depends on given machine parameters, like momentum compaction factor, acceleration voltage, and damping time. In this paper the influence of the damping time is studied by utilizing the CLIC damping wiggler prototype installed in KARA as well as by simulations using the Vlasov-Fokker-Planck solver Inovesa.
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-THPAK029  
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THPAK055 Suppression of Transverse Beam Instabilities by Stripline Kickers at TPS 3346
  • P.J. Chou, C.K. Chan, C.-C. Chang, K.T. Hsu, K.H. Hu, C.K. Kuan, I.C. Sheng, F.H. Tseng
    NSRRC, Hsinchu, Taiwan
  Collective beam instabilities could limit the accelerator performance if proper countermeasures are not in place. Active beam feedback systems are commonly used to suppress beam instabilities. The resistive wall impedance including phase-II insertion devices at TPS are calculated with analytical formulas. The growth rate of transverse coupled bunch instabilities due to wall impedance is estimated by theory. The RF properties of existing stripline kickers in TPS are analyzed with a 3-D electromagnetic simulation code GdfidL. Based on the above analysis, the requirements for a beam feedback system are calculated and the results are reported.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-THPAK055  
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