Keyword: damping
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MOYCA1 Ultimate Field Gradient in Metallic Structures klystron, linac, collider, linear-collider 24
 
  • W. Wuensch
    CERN, Geneva, Switzerland
  
  Significant progress has been made over the past decade by studies of normal-conducting linear colliders, NLC/JLC (Next/Japanese Linear Collider) and CLIC (Compact Linear Collider), to raise achievable accelerating gradient from the range of 20-30 MV/m up to 100-120 MV/m. The gain has come through a greatly increased understanding of high-power rf phenomena, development of quantitative high-gradient rf design methods, refinements in cavity fabrication techniques and through development of high peak rf power sources. Recently accelerating gradients in excess of 100 MV/m, at very low breakdown rates, have been successfully achieved with new techniques of conditioning in numerous prototypes at different laboratories. The talk will report on the impact of these new results on the understanding of the physics of breakdown and of conditioning, and on the ultimate gradients that can be expected in metallic RF structures.  
slides icon Slides MOYCA1 [52.087 MB]  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2017-MOYCA1  
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MOPAB005 The MultiMat Experiment at CERN HiRadMat Facility: Advanced Testing of Novel Materials and Instrumentation for HL-LHC Collimators target, experiment, instrumentation, real-time 76
 
  • F. Carra, A. Bertarelli, E. Berthomé, C. Fichera, J. Guardia, M. Guinchard, L.K. Mettler, S. Redaelli, O. Sacristan De Frutos
    CERN, Geneva, Switzerland
  • T.R. Furness
    University of Huddersfield, Huddersfield, United Kingdom
  • M. Portelli
    UoM, Msida, Malta
  
  Funding: *Part of the work described in this thesis was developed in the scope of the EuCARD-2 Project, WP11 'ColMat ' HDED', co-funded by the partners and the European Commission under Capacities 7th Framework Programme, Grant Agreement n. 312453. Research supported by the HL-LHC project.
The increase of the stored beam energy in future particle accelerators, such as the HL-LHC and the FCC, calls for a radical upgrade in the design, materials and instrumentation of Beam Intercepting Devices (BID), such as collimators Following successful tests in 2015 that validated new composite materials and a novel jaw design conceived for the HL-LHC collimators, a new HiRadMat experiment, named 'HRMT36-MultiMat', is scheduled for autumn 2017. Its objective is to determine the behaviour under high intensity proton beams of a broad range of materials relevant for collimators and beam intercepting devices, thin-film coatings and advanced equipment. The test bench features 16 separate target stations, each hosting various specimens, allowing the exploration of complex phenomena such as dynamic strength, internal damping, nonlinearities due to anisotropic inelasticity and inhomogeneity, effects of energy deposition and radiation on coatings. This paper details the main technical solutions and engineering calculations for the design of the test bench and of the specimens, the candidate target materials and the instrumentation system
#federico.carra@cern.ch 		 
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2017-MOPAB005  
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MOPAB037 Analytical and Numerical Performance Analysis of a Cryogenic Current Comparator cryogenics, dipole, simulation, beam-diagnostic 160
 
  • N. Marsic, H. De Gersem, W.F.O. Müller
    TEMF, TU Darmstadt, Darmstadt, Germany
  • F. Kurian, M. Schwickert, T. Sieber
    GSI, Darmstadt, Germany
  
  Funding: This research is funded by the German Bundesministerium für Bildung und Forschung as the project BMBF-05P15RDRBB Ultra-Sensitive Strahlstrommessung für zukünftige Beschleunigeranlagen.
Nowadays, cryogenic current comparators (CCCs) are among the most accurate devices for measuring extremely small electric currents. Probably the most interesting property of this equipment, is the excellent position independence of the current passing through it. This feature motivated the use of CCCs for beam instrumentation in particle accelerators. A typical CCC consists of a ferrite core, a pick-up coil, a superconducting quantum interference device, appropriate electronics and superconducting shielding consisting of a meander structure. This configuration offers a strong attenuation for all the magnetic field components, except for the azimuthal one. Thus, high precision measurements of extremely low beam currents are made possible. The damping performance of this device is analysed in this work. A 3D finite element (FE) analysis has been carried out and the computed results were compared to an analytical model*. Furthermore, in order to reduce the computation time, a 2.5D FE model is also proposed and discussed.
* K. Grohmann et al., Field attenuation as the underlying principle of
cryo-current comparators 2. Ring cavity elements, Cryogenics, vol. 16, no. 10, pp. 601-605, 1976. 		 
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2017-MOPAB037  
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MOPAB155 Characterization of the Longitudinal Acceptance in a Storage Ring with RF Pinger cavity, synchrotron, dynamic-aperture, storage-ring 497
 
  • G.M. Wang, B. Holub, Y. Li, J. Rose, T.V. Shaftan
    BNL, Upton, Long Island, New York, USA
  
  In modern generation light sources, it is desired to have SR performance at high beam current, low horizontal emittance with small coupling, resulting in intense Touschek scattering, which is the dominant limitation of beam lifetime. Touschek scattering strongly depends on momentum aperture. Understanding momentum aperture is extremely important. NSLS II storage ring RF system has the digital ramp control function, enabling rapid change of the cavity phase and amplitude. This makes the possibility to ping the beam in longitudinal phase space and directly measure the longitudinal acceptance, in contrast with traditional indirect way to understand it from other aspect of parameters. In this paper, we present the tool, longitudinal pinger, its application to characterize NSLS II longitudinal acceptance and localize the momentum aperture limit with SR BPMs.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2017-MOPAB155  
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MOPVA029 Conceptual Design of a Pre-Booster Ring for the FCC e+e− Injector emittance, booster, extraction, injection 917
 
  • O. Etisken, A.K. Çiftçi
    Ankara University, Faculty of Sciences, Ankara, Turkey
  • Y. Papaphilippou
    CERN, Geneva, Switzerland
  
  The FCC-ee injector complex needs to produce and to transport a high-intensity e+/e− beam at a fast repetition rate of about 0.1 Hz for topping up the collider at its collision energy. A basic parameter set exists for all the collider energies, assuming a 10 GeV linac operating with a large number of bunches being accumulated in the existing SPS, which serves as pre-accelerator and damping ring before the bunches are transferred to the high-energy booster. The purpose of this study is to provide the conceptual design of an alternative accelerator ring, replacing the SPS in the present scheme. This ring will have injection energy of around 5 GeV and extraction energy of around 20 GeV. Apart from establishing the basic parameters of the ring, the study work will include the optics design and layout, single particle linear and non-linear dynamics optimization, including magnetic and alignment error tolerances. The study will also contain some basic estimation of collective effects and address the issue of synchrotron radiation handling.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2017-MOPVA029  
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MOPVA053 The SRF Module Developments for BESSY VSR HOM, cavity, synchrotron, SRF 986
 
  • A.V. Vélez, H.-W. Glock, F. Glöckner, B.D.S. Hall, J. Knobloch, A. Neumann, P. Schnizer, E. Sharples, A.V. Tsakanian
    HZB, Berlin, Germany
  
  Helmholtz-Zentrum Berlin is developing BESSY VSR, a novel upgrade of the BESSY II facility to provide highly flexible pulse lengths while maintaining the flux and brilliance. The project goal is to simultaneously circulate both standard (some 10 ps long) and short (ps and sub-ps long) pulses offering the BESSY user community picosecond dynamics and high-resolution experiments. The concept relies on the installation of high-voltage SRF cavities operating at the 3rd and 3.5th harmonic whereby the beating of the two frequencies provides RF buckets for long and short bunches. Since these cavities will operate in CW and with high beam current (Ib=300 mA), the cavity design represents a challenging goal. In addition the need to avoid coupled bunch instabilities (CBI's), the installation of the VSR Cryomodule must fit in one of the available 4-m long low beta straights. To address the technological and engineering challenges techniques such as waveguide-damped cavities have been developed. First prototypes have been produced. In this paper, the present SRF developments are presented, including the cavities, high power couplers, higher-order mode absorbers and the cryomodule design.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2017-MOPVA053  
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MOPVA080 HOM Simulations and Damping Scheme for CEPC Cavities HOM, cavity, collider, impedance 1052
 
  • H.J. Zheng, J. Gao, F. Meng, P. Sha, J.Y. Zhai
    IHEP, Beijing, People's Republic of China
  
  In this paper, it will be presented that the higher order mode (HOM) analysis of the 650 MHz cavities for the Circular Electron-Positron Collider (CEPC). The higher order modes excited by the intense beam bunches must be damped to avoid additional cryogenic loss and multi-bunch instabilities. To keep the beam stable, the impedance budget and the HOM damping requirement are given. The conventional coaxial HOM coupler, which will be mounted on the beam pipe, is planned to extract the HOM power below the cut-off frequency of the beam pipe, and the propagating modes will be absorbed by the two HOM absorbers at room temperature outside the cryomodule.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2017-MOPVA080  
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TUPAB009 Design Study on CEPC Positron Damping Ring and Bunch Compressor linac, positron, emittance, injection 1318
 
  • D. Wang, Y.L. Chi, J. Gao, X.P. Li, C. Meng, J.R. Zhang
    IHEP, Beijing, People's Republic of China
  • G. Pei
    Institute of High Energy Physics (IHEP), Chinese Academy of Sciences, Beijing, People's Republic of China
  
  The primary purpose of CEPC damping ring is to reduce the transverse phase spaces of positron beam to suitably small value at the beginning of Linac and also adjust the time structure of positron beam for reinjection into the Linac. Longitudinal bunch length control was provided to minimize wake field effects in the Linac by a bunch compressor system after the damping ring. Both designs for damping ring and bunch compressor were discussed in this paper.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2017-TUPAB009  
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TUPAB014 Preliminary Design of FCC-ee Pre-Injector Complex linac, emittance, positron, booster 1337
 
  • S. Ogur, Y. Papaphilippou, F. Zimmermann
    CERN, Geneva, Switzerland
  • A.M. Barnyakov, A.E. Levichev, D.A. Nikiforov
    BINP SB RAS, Novosibirsk, Russia
  • K. Furukawa, N. Iida, F. Miyahara, K. Oide
    KEK, Ibaraki, Japan
  
  The design of a 100 km circular e+e− collider with extremely high luminosity is an important component of the global Future Circular Collider (FCC) study hosted by CERN. FCC-ee is being designed to serve as Z, W, H and top factory, covering beam energies from 45.6 to 175 GeV. For the injectors, the Z-operation is the most challenging mode, due to the high total charge and low equilibrium emittance in the collider at this energy. Thus, fulfilling the Z-mode will also meet the demands for all other modes of FCC-ee. This goal can be achieved by using a 6 GeV NC linac with an S-band RF frequency of 2.856 GHz and a repetition rate of 100 Hz. This linac will accelerate two bunches per RF pulse, each with a charge of 6.5 nC. Positrons will be generated by sending 4.46 GeV e- onto a hybrid target so that the e+ created can still be accelerated to 1.54 GeV in the remaining part of the same linac. The emittance of the e+ beam will then shrink to the nm level in a 1.54 GeV damping ring. After damping, the e+ will be reinjected into the linac and accelerated to 6 GeV. The e- and e+ will then be accelerated alternately to 45.6 GeV in the booster, before they are injected into the collider.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2017-TUPAB014  
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TUPAB146 Vibration Measurements of Super-Conducting Undulator at SSRF undulator, data-analysis, data-acquisition, experiment 1675
 
  • R.B. Deng, Y. Liu, L. Wang, S. Xiang
    SINAP, Shanghai, People's Republic of China
  
  Funding: Work supported by the National Natural Science Foundation of China (Grant No. 11405255)
A Super-Conducting Undulator (SCU) is being built at SSRF. Mechanical stability of SCU is critical to beam stability since the central load is supported by special strings in SCU and the vibration of load will cause directly the vibration of beam. In this paper, vibration results of several key components including central load, cold head, frame support, etc, are studied under different working mode of compressors. The ground vibrations at different distances are compared to get the influence of compressors to SCU. Useful suggestions and possible measures are described to mitigate the vibration and improve SCU stability. 		 
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2017-TUPAB146  
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TUPIK094 Transverse Feedback Parameter Extraction from Excitation Data feedback, kicker, pick-up, operation 1920
 
  • G. Kotzian
    CERN, Geneva, Switzerland
  
  In this paper we present a simple and fast approach to extract essential parameters of a transverse feedback system such as phase advances between pick-ups and kickers, fractional tune, kicker delay, or per-bunch transverse activity from discrete-time samples of position signals. In this approach the beam is excited and subsequent beam oscillations are recorded. Given that any number of pick-ups can be evaluated at once with only a marginal increase of transverse beam size this method is suitable for regular health checks of a transverse feedback system, e.g., for every injection. The fundamental idea relies on the reconstruction of the transverse phase space by means of digital filters. We sketch a simple mathematical model to illustrate the underlying method. Examples are given together with a set of filter kernels for the fractional tunes of the LHC transverse feedback system.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2017-TUPIK094  
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TUPIK095 Possibilities for Transverse Feedback Phase Adjustment by Means of Digital Filters pick-up, feedback, kicker, betatron 1924
 
  • G. Kotzian
    CERN, Geneva, Switzerland
  
  In transverse feedback systems a phase adjustment is generally required to convert a beam position signal from a pick-up into a momentum correction signal used by a transverse kicker. In this paper we outline several possibilities for phase adjustments using only single pick-ups or the vector combination of two pick-ups. Analytical expressions are given as a function of the fractional tune and the betatron phase advance between the pick-up location and the kicker. The shortest possible digital filter is formulated, including a notch for closed orbit suppression and a free parameter to adjust for betatron phase. We introduce a novel, fully parametrized digital filter with the feature to be insensitive to variations in fractional tune. Examples are given for the SPS transverse feedback system and compared with measurements.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2017-TUPIK095  
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TUPVA029 Observations of Emittance Growth in the Presence of External Noise in the LHC emittance, simulation, brightness, experiment 2117
 
  • X. Buffat, C. Tambasco, D. Valuch
    CERN, Geneva, Switzerland
  • J. Barranco García, T. Pieloni, C. Tambasco
    EPFL, Lausanne, Switzerland
  
  Dedicated experiments were perfomed in the LHC to study the impact of noise on colliding high brightness beams. The results are compared to theoretical models and multiparticle tracking simulations. The impacts on the LHC operation and the HL-LHC project are discussed.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2017-TUPVA029  
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TUPVA031 Impact of Incoherent Effects on the Landau Stability Diagram at the LHC octupole, betatron, coupling, simulation 2125
 
  • C. Tambasco, J. Barranco García, X. Buffat, T. Pieloni
    CERN, Geneva, Switzerland
  • J. Barranco García, X. Buffat, T. Pieloni
    EPFL, Lausanne, Switzerland
  
  Instability thresholds are explored at the Large Hadron Collider (LHC) by means of the computation of the Landau Stability Diagrams (SD). In the presence of diffusive mechanisms, caused by resonance excitations or noise, the SD can be reduced due to the modification of the particle distribution inside the beam. This effect can lead to a possible lack of Landau damping of the coherent modes previously damped by lying within the unperturbed SD area. The limitations deriving from coherent instabilities in the LHC is crucial in view of future projects that aim to increase the performance of the LHC such as the High-Luminosity upgrade (HL-LHC). Simulation tools for the computation of the SD have been extended in order to take into account the incoherent effects from long tracking through the detailed model of the accelerator machine. The model includes among others beam-beam interactions and octupoles and the interplay between both is addressed. Finally the simulation results are compared to the Beam Transfer Function (BTF) measurements in the LHC.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2017-TUPVA031  
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WEOAB3 RF Quadrupole Structures for Transverse Landau Damping in Circular Accelerators quadrupole, simulation, impedance, collider 2516
 
  • M. Schenk, X. Buffat, L.R. Carver, A. Grudiev, K.S.B. Li, E. Métral, K. Papke
    CERN, Geneva, Switzerland
  • A. Maillard
    ENS, Paris, France
  
  The beams required for the high luminosity upgrade of the Large Hadron Collider (HL-LHC) and other potential future circular colliders (FCC) call for efficient mechanisms to suppress transverse collective instabilities. In addition to octupole magnets installed for the purpose of Landau damping in the transverse planes, we propose to use radio frequency (rf) quadrupole structures to considerably enhance the aforementioned stabilising effect. By means of the PyHEADTAIL macroparticle tracking code as well as analytical studies, the stabilising mechanism introduced by an rf quadrupole is studied and explained. It is, furthermore, compared to the influence of the second order chromaticity on transverse beam stability.  
slides icon Slides WEOAB3 [2.537 MB]  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2017-WEOAB3  
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WEPAB067 Electron Beam Lifetime in SOLARIS Storage Ring electron, storage-ring, scattering, vacuum 2731
 
  • M.B. Jaglarz, P.B. Borowiec, A. Kisiel, A.I. Wawrzyniak
    Solaris, Kraków, Poland
  • A.M. Marendziak
    Solaris National Synchrotron Radiation Centre, Jagiellonian University, Kraków, Poland
  
  Solaris storage ring is a recently constructed and commissioned machine. At the beginning of storage ring operation the lifetime was very short mostly dominated by the ion trapping and residual gas scattering. After a 390 A·h of beam cleaning the measured total lifetime has reached 20 h for 100mA of a stored current. Since the main contribution to the total lifetime in the storage ring comes from single Coulomb and Touschek scattering the dependence of the residual gas pressure and the vertical aperture of storage ring is investigated. Moreover to improve the Touschek lifetime the 3rd harmonic cavities were installed. Recently the cavities were tuned close to the resonance and the total lifetime increased significantly. This presentation will report on the lifetime measurements and calculations carried out for Solaris 1.5 GeV storage ring at different vacuum and RF conditions.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2017-WEPAB067  
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WEPAB115 Normal Conducting CW Transverse Crab Cavity For Producing Short Pulses In SPEAR3 cavity, HOM, impedance, photon 2840
 
  • Z. Li, V.A. Dolgashev, M. Dunham, K.J. Gaffney, R.O. Hettel, X. Huang, N. Kurita, J.A. Safranek, J.J. Sebek, K. Tian
    SLAC, Menlo Park, California, USA
  
  Funding: This work was supported by DOE Contract No. DE-AC02-76SF00515.
The ability to produce short pulse X-rays on the scale of 1-10 ps fwhm in the SPEAR3 storage ring light source would enable enhanced timing mode studies of dynamic processes in materials as they occur. The crab cavity approach appears to be optimal for SPEAR3 to produce short pulse X-rays. Furthermore, by using a two-frequency crabbing scheme, SPEAR3 would be able to produce short-pulse bunches while supplying the high average flux needed for regular users. While supercon-ducting RF (SCRF) technology could be a natural choice for the CW crab cavity, the deflecting voltage for SPEAR3 crabbing appears to be within reach of more affordable normal conducting RF (NCRF). In this paper, we present a preliminary NCRF CW crab cavity design for SPEAR3. 		 
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2017-WEPAB115  
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WEPIK062 UNDUMAG - A New Computer Code to Calculate the Magnetic Properties of Undulators undulator, synchrotron, synchrotron-radiation, radiation 3071
 
  • M. Scheer
    HZB, Berlin, Germany
  
  A new code for the magnetic design of undulators is under development at the Helmholtz-Zentrum Berlin (BESSY). The program reads in the geometry and material properties of the undulator magnets and iron poles. Magnetic fields, forces and torques, as well as trajectories and synchrotron radiation can be calculated. The code is a stand-alone FORTRAN program, thus, only a FORTRAN compiler is needed to install it. Build-in graphic routines allows to write postscript files to visualize the geometry and the fields. Other results like 3D field maps, field integrals etc. are written to ASCII files for later use. The code will be published under the GNU general public license. First results and comparison to other codes are presented.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2017-WEPIK062  
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WEPIK068 Non-Linear Beam Dynamics Studies of the CLIC Damping Wiggler Prototype wiggler, operation, optics, storage-ring 3087
 
  • J. Gethmann, A. Bernhard, E. Blomley, E. Huttel, A.-S. Müller, A.I. Papash, M. Schedler
    KIT, Karlsruhe, Germany
  • Y. Papaphilippou, P. Zisopoulos
    CERN, Geneva, Switzerland
  • K. Zolotarev
    BINP SB RAS, Novosibirsk, Russia
  
  Funding: Julian Gethmann acknowledges the support by the DFG-funded Doctoral School Karlsruhe School of Elementary and Astroparticle Physics: Science and Technology
First beam dynamics studies of a damping wiggler prototype for the CLIC damping rings have been carried out at the KIT storage ring. Effects of the 2.9 T superconducting wiggler on the electron beam in the 2.5 GeV standard operation mode have been measured and compared with theoretical predictions. Higher order multipole components were investigated using local orbit bump measurements. Based on these findings the simulation models for the storage ring optic have been adjusted. The refined optics model has been applied to the 1.3 GeV, low-operation case. This case will be used to experimentally benchmark beam dynamics simulations involving strong wiggler fields and dominant collective effects. We present these measurements, comparisons and the findings of the simulations with the updated low-mode optics model. 		 
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2017-WEPIK068  
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WEPIK102 Measurement of RF Resonances and Measured Impact on Transverse Multibunch Instabilities from In-vacuum Insertions Devices vacuum, resonance, coupling, dipole 3188
 
  • G. Rehm
    DLS, Oxfordshire, United Kingdom
  
  Diamond Light Source has currently 15 in-vacuum insertion devices (ID) installed, mostly built in-house. Their measured impact on multi-bunch mode damping as a result of varying magnet gap was shown before, now we augment these with measurements of broadband frequency spectra with stored beam obtained using an antenna placed in the ID vacuum. Finally, we present off-line measurements of resonances in the ID vessel acquired using a vector network analyser and two antennae installed in-vacuum.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2017-WEPIK102  
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WEPIK116 Aberration Compensation in a Skew Parametric-Resonance Ionization Cooling Channel multipole, resonance, simulation, sextupole 3221
 
  • A.V. Sy, Y.S. Derbenev, V.S. Morozov
    JLab, Newport News, Virginia, USA
  • A. Afanasev
    GWU, Washington, USA
  • Y. Bao
    UCR, Riverside, California, USA
  • R.P. Johnson
    Muons, Inc, Illinois, USA
  
  Funding: This work was supported in part by U.S. DOE STTR Grant DE-SC0005589. Authored by Jefferson Science Associates, LLC under U.S. DOE Contract No. DE-AC05-06OR23177.
Skew Parametric-resonance Ionization Cooling (Skew PIC) represents a novel method for focusing of highly divergent particle beams, as in the final 6D cooling stage of a high-luminosity muon collider. In the muon collider concept, the resultant equilibrium transverse emittances from cooling with Skew PIC are an order of magnitude smaller than in conventional ionization cooling. The concept makes use of coupling of the transverse dynamic behavior, and the linear dynamics are well-behaved with good agreement between analytic solutions and simulation results. Compared to the uncoupled system, coupling of the transverse dynamic behavior purports to reduce the number of multipoles required for aberration compensation while also avoiding unwanted resonances. Aberration compensation is more complicated in the coupled case, especially in the high-luminosity muon collider application where equilibrium angular spreads in the cooling channel are on the order of 200 mrad. We present recent progress on aberration compensation for control of highly divergent muon beams in the coupled correlated optics channel, and a simple cooling model to test the transverse acceptance of the channel. 		 
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2017-WEPIK116  
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WEPVA098 Measurements on a 12.5 kV Prototype Inductive Adder for the CLIC DR Extraction Kickers flattop, kicker, extraction, collider 3487
 
  • J. Holma, M.J. Barnes
    CERN, Geneva, Switzerland
  
  The CLIC study is investigating the technical feasibility of an electron-positron collider with high luminosity and a nominal centre-of-mass energy of 3 TeV. The pre-damping rings and damping rings (DRs) will produce ultra-low emittance beam with high bunch charge. To avoid beam emittance increase, the DR kicker systems must provide extremely stable field pulses during injection and extraction of bunches. The DR extraction kicker system consists of a stripline kicker and two pulse modulators. The current specifications for the modulators call for pulses with 160 ns or 900 ns flattop duration of ±12.5 kV and 305 A, with ripple of not more than ±0.02 % (±2.5 V). An inductive adder is a very promising approach to meeting the specifications because analogue modulation methods can be applied to adjust the output waveform. Recently, the first full-scale, 20-layer, 12.5 kV prototype inductive adder has been assembled at CERN and testing has commenced. The goal is to tailor the output waveform of the prototype to the waveform required for the DR extraction stripline kicker. The results of the initial tests and measurements are presented.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2017-WEPVA098  
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THOBA3 A Compact 335 MeV Positron Damping Ring Design for FACET-II positron, emittance, linac, quadrupole 3652
 
  • G.R. White, Y. Cai, R.O. Hettel, M.A.G. Johansson, V. Yakimenko, G. Yocky
    SLAC, Menlo Park, California, USA
  
  Funding: This work was supported by the Department of Energy under Contract Number: DE-AC02-76SF00515.
FACET-II will be a new test facility, starting construction in 2018 within the main SLAC Linac. Its purpose is to build on the decades-long experience developed conducting accelerator R&D at SLAC in the areas of advanced acceleration and coherent radiation techniques with high-energy electron and positron beams. The positron system design utilizes an existing W-Re target in Linac Sector 19, driven by 4 nC electrons bunches at 10 GeV. We present the design of a 335 MeV, 21.4 m circumference damping ring required to damp emittance from a modified positron return beamline by a factor of 500. The transverse emittance is calculated to be 6 um-rad, fully coupled, with a bunch length of 4 mm and energy spread 0.06 %, at a bunch charge of 1 nC. The arc magnets need to be especially compact due to tight space constraints (installation will be in the existing SLAC Linac tunnel, Sector 10, with 3 m width available) and were a key design challenge. We present a solution with combined function bend/quadrupole/sextupole magnets which have been modelled in 3D using Opera. 		 
slides icon Slides THOBA3 [8.372 MB]  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2017-THOBA3  
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THPAB007 Short Bunches at the Transition From Strong to Weak Longitudinal Instability shielding, simulation, synchrotron, experiment 3696
 
  • P. Kuske
    HZB, Berlin, Germany
  
  The interaction of particles with their vacuum sur-roundings can lead to longitudinal instabilities of the whole bunch of particles. Most of these instabilities are strong and the growth rates are large compared to the damping rate. For a weak instability the opposite is true and with just a resistive impedance the instability would always be weak and independent of the bunch length. The interaction of a bunch with its own radiation emitted midway between parallel plates leads to a strong instabil-ity for long bunches and a transition to weak instability if the bunch length becomes shorter. This regime is ana-lysed numerically with a Vlasov-Fokker-Planck solver. The results are compared to recent observations at ANKA. An attempt is made to explain the remaining discrepan-cies by including higher order terms of the momentum compaction factor into these calculations. There are indi-cations that the simple model needs refinements in order to take radiation from upstream dipoles into account.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2017-THPAB007  
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THPAB030 Studies on Collective Instabilities in HEPS impedance, injection, operation, ion 3763
 
  • N. Wang, Z. Duan, C. Li, S.K. Tian, H.S. Xu
    IHEP, Beijing, People's Republic of China
  
  The High Energy Photon Source (HEPS) is a new designed photon source at beam energy of 6 GeV. Due to the small beam size and increased coupling impedance with the restricted beam pipe aperture, the collective effects may bring new challenges to the physical design of the machine. The collective instabilities are estimated for different operation mode. The critical instability issues are also identified for each mode.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2017-THPAB030  
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THPAB039 Novel Manufacturing Concepts for 12 GHz High Gradient Accelerating Structures vacuum, operation, alignment, linac 3787
 
  • A. Solodko, S. Atieh, N. Catalán Lasheras, A. Grudiev, S. Lebet, W. Wuensch
    CERN, Geneva, Switzerland
  • H. Zha
    TUB, Beijing, People's Republic of China
  
  CLIC high gradient accelerating structures (AS) work-ing in X-band are made of copper ultra-high precision discs, requiring both milling and turning operations. Discs are then joint together by diffusion bonding. The rest of important technical systems, such as vacuum, cooling and manifolds, to house damping silicon carbide absorbers, are brazed to the bonded disc stack afterwards. This manufacturing technique has been successfully demonstrated but it is very challenging and needs an accurate assembly at every production step. Main issues concern vacuum-tightness, misalignment, deformations during different assembly operations, defects of braz-ing/bonding operations (gaps, a leak of brazing material) etc. Preparation and repairs are time and resource con-suming and increase the final price of the accelerating structure. This paper describes the novel manufacturing concepts for 12 GHz high gradient AS and focuses on new joining techniques as electron beam welding or brazing, new engineering solutions, as rectangular cells or structures made of halves are being considered.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2017-THPAB039  
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THPAB040 Destabilising Effect of Linear Coupling in the LHC coupling, simulation, octupole, operation 3791
 
  • L.R. Carver, D. Amorim, N. Biancacci, X. Buffat, K.S.B. Li, E. Métral, B. Salvant, M. Schenk
    CERN, Geneva, Switzerland
  
  During operation in 2015 and 2016, some transverse instabilities were observed when either the coupling (or closest tune approach) C- was large, or when the tunes were moved closer together. This motivated a campaign of simulations on the effect of linear coupling on the transverse stability. Measurements made during operation and with dedicated beam time have been found to confirm the predictions. This paper will detail the results of the linear coupling studies and relate them to operation of the LHC in the future.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2017-THPAB040  
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THPAB115 Development of a Longitudinal Feedback System for Coupled Bunch Instabilities Caused by the Accelerating Mode at Superkekb cavity, impedance, operation, target 3989
 
  • K. Hirosawa, K. Akai, E. Ezura, T. Kobayashi, K. Nakanishi, M. Nishiwaki, S.I. Yoshimoto
    KEK, Ibaraki, Japan
  
  SuperKEKB is an asymmetric energy electron-positron circular collider. Phase-I commissioning was operated from February to June in 2016. The purpose of this accelerator is to aim at the higher luminosity than KEKB, so a larger beam current is made for it. In the future plan, beam currents in the electron and positron rings will be increased to 2.6A and 3.6A, respectively. As we consider beam dynamics in the storage ring, higher mode instability associated with the accelerating mode will be caused by a large beam current. Especially the target instability of this study is called μ=-2 mode Coupled Bunch Instability. To suppress it, we developed new feedback components for longitudinal coupled bunch instability. We have same mechanism feedback components for KEKB, but it supports only μ=-1 mode instability. Since a large current makes μ=-1 mode instability big, there is a possibility that suppression is difficult only by using KEKB components. In order to deal with this problem, new components we developed support μ=-1, -2, and -3 mode instabilities, and we improved the performance and usability as compared to existing components. We schedule studies using a beam at Phase-II.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2017-THPAB115  
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THPIK036 Design Study of Damped Accelerating Cavity Based on the TM020-Mode and HOM Couplers for the KEK Light Source Project cavity, HOM, target, simulation 4172
 
  • T. Takahashi, S. Sakanaka, N. Yamamoto
    KEK, Ibaraki, Japan
  
  A novel damped-cavity scheme was recently proposed by Ego et al.*. In this design, TM020 resonant mode is used for beam acceleration. Power of higher-order (or lower-order) modes are extracted through cylindrical slots which are placed at the position where the magnetic fields of HOMs are strong while that of TM020 mode is zero. Extracted powers are absorbed by lossy ferrites. In this scheme, excellent HOM damping is possible while occupying less space of the straight section in storage rings. We propose in this paper an alternative design which is based on the same TM020 mode but with rod-type HOM couplers. The rod-type HOM couplers are placed where the electric fields of HOMs are strong while that of TM020 mode is zero. In this scheme, openings needed for HOM extraction can be made smaller, which is desirable for stiffening the mechanical structure of the cavity. Potential use of lossy dielectric materials is another merit. We present external Q-values of HOMs that can be achieved in this scheme, as well as an effect of HOM couplers on the TM020 mode. Our current study is directed to a 1.5 GHz higher-harmonic cavity for the proposed KEK Light Source project**.
* H. Ego et al., in Proceedings of the 11-th Annual Meeting of Particle Accelerator Society of Japan, Aug. 9-11, 2014, MOOL14 [in Japanese].
** K. Harada et al., IPAC2016, THPMB012.
 		 
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2017-THPIK036  
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THPIK078 1.5 GHz Cavity Design for the CLIC Damping Ring and as Active Third Harmonic Cavity for ALBA cavity, HOM, impedance, simulation 4263
 
  • B. Bravo, J.M. Alvarez, F. Pérez, A. Salom
    ALBA-CELLS Synchrotron, Cerdanyola del Vallès, Spain
  
  In a collaboration framework between CERN and ALBA, we are designing a normal conducting active 1.5 GHz cavity which could serve as main RF system for the Damping Ring of CLIC and as an active third harmonic cavity for the ALBA Storage Ring. The third harmonic cavity at ALBA will be used to increase the bunch length in order to improve the beam lifetime and increase the beam stability thresholds. The main advantage of an active third harmonic cavity is that optimum conditions can be reached for any beam current. This paper presents the preliminary design of this cavity: an active, normal conducting cavity tuned at 1.5 GHz based on the 500 MHz European Higher Order Mode (HOM) damped normal conducting with nose cones using ridged circular waveguides for HOM damping. Electromagnetic simulations, mechanical and thermal stress analysis will be presented together with the calculations on beam stability improvement due to the third harmonic system.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2017-THPIK078  
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THPVA002 Numerical Investigation of Beam Halo From Beam Gas Scattering in KEK-ATF emittance, simulation, scattering, vacuum 4410
 
  • R.J. Yang, P. Bambade
    LAL, Orsay, France
  • K. Kubo, T. Okugi, N. Terunuma, D. Zhou
    KEK, Ibaraki, Japan
  
  To demonstrate the final focus schemes of the Future Linear Collider (FLC), the Accelerator Test Facility 2 (ATF2) at KEK is devoted to focus the beam to a RMS size of a few tens of nanometers (nm) vertically and to provide stability at the nm level at the virtual Interaction Point (IP). However, the loss of halo particles upstream will introduce background to the diagnostic instrument measuring the ultra-small beam, using a laser interferometer monitor. To help the realization of the above goals and beam operation, understanding and mitigation of beam halo are crucial. In this paper, we present the systematical simulation of beam halo formation from beam gas Coulomb scattering (BGS) in the ATF damping ring. The behavior of beam halo with various machine parameters is also discussed.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2017-THPVA002  
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THPVA012 Transverse Impedance Measurement in SuperKEKB impedance, betatron, operation, storage-ring 4442
 
  • N. Kuroo
    UTTAC, Tsukuba, Ibaraki, Japan
  • T. Ishibashi, T. Mimashi, K. Ohmi, Y. Ohnishi, K. Shibata, Y. Suetsugu, S. Terui, M. Tobiyama, D. Zhou
    KEK, Ibaraki, Japan
  
  In KEK(Japan), SuperKEKB project is progressing toward upgrade. This project aims improvement luminosity (8×1035 cm-2s- 1) which is 40 times of the performance of the KEKB accelerator. In Phase 1 of this project, a performance test as storage ring was carried out. Understanding of ring Impedance/wake is an important subject in phase I. Measurement of Head Tail Damping using Turn by Turn monitor was performed to evaluate impedance/wake. Betatron motion is excited by kicker and its damping is measured for several parameters sets of bunch current and chromaticity in both HER and LER. The wake field was calculated from the decrement of betatron amplitude. We present the wake field which is cross-checked with tune shift based on the current dependence.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2017-THPVA012  
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THPVA022 Comparison of Different Methods to Calculate Induced Voltage in Longitudinal Beam Dynamics Codes impedance, simulation, wakefield, dipole 4465
 
  • D. Quartullo, J. Repond
    CERN, Geneva, Switzerland
  • M. Migliorati
    University of Rome La Sapienza, Rome, Italy
  
  Collective effects in longitudinal beam dynamics simulations are essential for many studies since they can perturb the RF potential, giving rise to instabilities. The beam induced voltage can be computed in frequency or time domain using a slicing of the beam profile. This technique is adopted by many codes including CERN BLonD. The slicing acts as a frequency filter and cuts high frequency noise but also physical contributions if the resolution is not sufficient. Moreover, a linear interpolation usually defines the voltage for all the macro-particles, and this can be another source of unphysical effects. The MuSiC code describes interaction between the macro-particles with the wakes generated only by resonator impedances. The complications related to the slices are avoided, but the voltage can contain high frequency noise. In addition, since the computational time scales with the number of resonators and macro-particles, having a large number of them can be cumbersome. In this paper the features of the different approaches are described together with benchmarks between them and analytical formulas, considering both single and multi-turn wakes.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2017-THPVA022  
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THPVA026 Practical Stabilisation of Transverse Collective Instabilities with Second Order Chromaticity in the LHC simulation, octupole, sextupole, impedance 4477
 
  • M. Schenk, D. Amorim, N. Biancacci, X. Buffat, L.R. Carver, R. De Maria, K.S.B. Li, E. Métral, B. Salvant
    CERN, Geneva, Switzerland
  
  The study reports on dedicated measurements made with a single nominal bunch in the LHC at 6.5 TeV. First, we show that a significant amount of second order chromaticity Q'' can be introduced in the machine in a well-controlled manner. Second, we demonstrate that the incoherent betatron tune spread from Q'' can provide beam stability through the Landau damping mechanism. This is a first step in the development of a Q'' knob to be potentially applied during regular physics operation in the LHC.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2017-THPVA026  
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THPVA028 Multi-Bunch Instabilities Measurement and Analysis at the Diamond Light Source impedance, vacuum, insertion-device, insertion 4485
 
  • R. Bartolini, R.T. Fielder, E. Koukovini-Platia, G. Rehm
    DLS, Oxfordshire, United Kingdom
  
  The characterisation of the multi-bunch dynamics at the Diamond light source is performed with an advanced TMBF system that is capable of operating fast grow damp experiments thus allowing the exploration of many machine conditions. We report here the latest results of the measurement campaign, the implication on the machine impedance model and some of the intricacies of the analysis and interpretation of the experimental data.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2017-THPVA028  
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THPVA034 Comparison of the Coupling of Dipole Motion From Bunch to Bunch in an Electron Beam Caused by Electron Clouds at CesrTA Due to Variations in Bunch Length and Chromaticity electron, positron, dipole, coupling 4509
 
  • M.G. Billing, L.Y. Bartnik, J.A. Crittenden, M.J. Forster, N.T. Rider, J.P. Shanks, M.B. Spiegel, S. Wang
    Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA
  • R. Holtzapple
    CalPoly, San Luis Obispo, California, USA
  • E.C. Runburg
    University of Notre Dame, Indiana, USA
  
  Earlier experiments at the Cornell Electron-Positron Storage Ring Test Accelerator (CesrTA) have probed the interaction of the electron cloud (EC) with a 2.1 GeV stored positron beam. Since a very low EC density is expected with the electron bunches, these results characterize the dependence of beam-vacuum chamber impedance interactions, which are common to both positron and electron beams. The experiments were performed on a 30-bunch electron train with a 14 ns spacing, at a fixed current of 0.75mA/bunch, at two different vertical chromaticity settings and for four different bunch lengths (or synchrotron tunes.) The beam dynamics of the stored beam, in the presence of the electron cloud, was quantified using: 20 turn-by-turn beam position monitors in CESR to measure the correlated bunch-by-bunch dipole motion and an x-ray beam size monitor to record the bunch-by-bunch, turn-by-turn vertical size of each bunch within the trains. In this paper we report on the analysis of the observations from these experiments and compare them with effects of the EC on the positron beam's dipole motion and coupling of the motion from each bunch to its succeeding bunches.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2017-THPVA034  
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THPVA035 Dependence of the Coupling of Dipole Motion From Bunch to Bunch Caused by Electron Clouds at CesrTA Due to Variations in Bunch Length and Chromaticity electron, positron, dipole, synchrotron 4512
 
  • M.G. Billing, L.Y. Bartnik, J.A. Crittenden, M.J. Forster, N.T. Rider, J.P. Shanks, M.B. Spiegel, S. Wang
    Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA
  • R. Holtzapple
    CalPoly, San Luis Obispo, California, USA
  • E.C. Runburg
    University of Notre Dame, Indiana, USA
  
  The Cornell Electron-Positron Storage Ring Test Accelerator (CesrTA) has conducted experiments to probe the interaction of the electron cloud (EC) with a 2.1 GeV stored positron beam. These experiments investigate the dependence of beam'electron cloud interactions vs. bunch length (or synchrotron tune) at two values of the vertical chromaticity. The experiments utilized a 30-bunch positron train with a 14 ns spacing, at a fixed current of 0.75mA/bunch. The beam dynamics of the stored beam, in the presence of the electron cloud, was quantified using: 20 turn-by-turn beam position monitors in CESR to measure the correlated bunch-by-bunch dipole motion and an x-ray beam size monitor to record the bunch-by-bunch, turn-by-turn vertical size of each bunch within the trains. In this paper we report on the observations from these experiments and a more detailed analysis for the coupling of dipole motion via the EC from each bunch to succeeding bunches in the train.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2017-THPVA035  
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