Keyword: damping
Paper Title Other Keywords Page
MOOCA03 Updates to the International Linear Collider Damping Rings Baseline Design lattice, electron, positron, cavity 32
 
  • S. Guiducci, M.E. Biagini
    INFN/LNF, Frascati (Roma), Italy
  • G. Dugan, M.A. Palmer, D. L. Rubin
    CLASSE, Ithaca, New York, USA
  • J. Gao, D. Wang
    IHEP Beijing, Beijing, People's Republic of China
  • M.T.F. Pivi, Y. Sun
    SLAC, Menlo Park, California, USA
  • J. Urakawa
    KEK, Ibaraki, Japan
  
  A new baseline design for the International Linear Collider (ILC) damping rings has been adopted which reduces the ring circumference to 3.2 km from 6.4 km. This design change is associated with a revised plan to operate the ILC with one half the beam current originally specified in the ILC Reference Design Report. We describe the new layout and lattice that has been developed for the shorter ring. In addition, we discuss features of the new design that will allow operation at a 10Hz repetition rate which is twice the rate specified for baseline operation. Finally, we examine the implications for restoring operation with the originally specified beam current while maintaining the smaller ring circumference.  
slides icon Slides MOOCA03 [2.381 MB]  
 
MOODA01 Experience with the Cornell ERL Injector SRF Cryomodule during High Beam Current Operation cavity, HOM, SRF, cryomodule 35
 
  • M. Liepe, D.L. Hartill, G.H. Hoffstaetter, S. Posen, P. Quigley, V. Veshcherevich
    CLASSE, Ithaca, New York, USA
  
  Funding: Supported by NSF award DMR-0807731
Cornell University has developed and fabricated a SCRF injector cryomodule for the acceleration of high current, low emittance CW beams. This cryomodule is based on superconducting RF technology with five 2-cell SRF cavities operated in CW mode. Strong Higher-Order-Mode (HOM) damping and high power RF input couplers support accelerating beam currents of tens of mA. The cryomodule is currently under extensive testing in the Cornell ERL injector prototype with CW beam currents exceeding 25 mA. This paper gives an overview of the experience gained during the high beam current operation of the cryomodule, with a focus on the intrinsic cavity quality factors, input coupler performance, and HOM damping. 		 
 
MOPC021 Design of a Choke-mode Damped Accelerating Structure for CLIC Main Linac impedance, wakefield, HOM, dipole 113
 
  • J. Shi, A. Grudiev, W. Wuensch
    CERN, Geneva, Switzerland
  • H. Chen, W.-H. Huang, C.-X. Tang, H. Zha
    TUB, Beijing, People's Republic of China
  
  Choke-mode damped accelerating structures are being studied as an alternative to the CLIC baseline structure by a CERN-Tsinghua collaboration. Choke-mode structures hold the potential for much lower levels of pulsed surface heating and, since milling is not needed, reduced cost. Structures with radial choke attached are simulated in Gdfidl to investigate the damping of the transverse wake. The first pass-band of the dipole modes is well damped, while the higher order dipole modes are possible to be reflected by the choke. Therefore, the geometry of the choke is tuned to minimize the reflection of these higher order dipoles. Based on this damping scheme, an accelerating structure with the same iris dimensions as the nominal CLIC design but with choke-mode damping has been designed. A prototype structure will be manufactured and high power tested in the near future.  
 
MOPC037 Engineering Design and Fabrication of X-band Damped Detuned Structure for the CLIC Study vacuum, alignment, controls, wakefield 154
 
  • V. Soldatov, D. Gudkov, A. Samoshkin
    JINR, Dubna, Moscow Region, Russia
  • S. Atieh, A. D'Elia, A. Grudiev, G. Riddone
    CERN, Geneva, Switzerland
  • R.M. Jones, V.F. Khan
    UMAN, Manchester, United Kingdom
  
  A Damped Detuned Structure (DDS), known as CLICDDSA*, has been designed for the Compact Linear Collider (CLIC) study, and is presently under fabrication. The wakefield in DDS structures is damped using a combination of detuning the frequencies of beam-excited higher order modes and by light damping, through slot-coupled manifolds. The broad principles of the design are similar to that used in the NLC/GLC**. This serves as an alternative to the present baseline CLIC design which relies on heavy damping. CLICDDSA is conceived to be tested for its capacity to sustain high gradients at CERN. This structure operates with a 120 degrees phase advance per cell. We report on engineering design and fabrication details of the structure consisting of 24 regular cells plus 2 matching cells at both ends, all diffusion bonded together. This design takes into account practical mechanical engineering issues and is the result of several optimizations since the earlier CLICDDS designs.
* V. F. Khan et al., “Recent Progress on a Manifold Damped and Detuned Structure for CLIC”, Proc. of IPAC10, WEPE032, p. 3425 (2010).
** R.M. Jones et al., Phys. Rev. STAB 9, 102001 (2006). 		 
 
MOPC038 Engineering Design and Fabrication of Tapered Damped X-band Accelerating Structures vacuum, wakefield, alignment, HOM 157
 
  • A. Solodko, D. Gudkov, A. Samoshkin
    JINR, Dubna, Moscow Region, Russia
  • S. Atieh, A. Grudiev, G. Riddone, M. Taborelli
    CERN, Geneva, Switzerland
  
  The accelerating structures (AS) are one of the main components of the Compact LInear Collider (CLIC), under study at CERN. Each AS contains about 30 copper disks, which form the accelerating cavity. A fully featured AS is very challenging and requires several technologies. Different damping methods, waveguides, vacuum manifolds, slots and choke, result in various design configurations. In the CLIC multibunch AS, called TDS (Tapered Damped Structure), each cell is damped by its four waveguides, which are extended by channels machined in dedicated external vacuum manifolds. The manifolds combine few functions such as damping, vacuum pumping and cooling. Silicon carbide absorbers, fixed inside of each manifold, are required for effective damping of High Order Modes. CERN is producing X-band RF structures in close collaboration with a large number of laboratories taking advantage of their large expertise and test facilities. The fabrication includes several steps from the machining to the final assembly, including quality controls. This paper describes the engineering design and fabrication procedure of the X-band AS with damping material, by focusing on few technical solutions.  
 
MOPC054 The LHC RF System - Experience with Beam Operation synchrotron, injection, klystron, emittance 202
 
  • P. Baudrenghien, M. E. Angoletta, T. Argyropoulos, L. Arnaudon, J. Bento, T. Bohl, O. Brunner, A.C. Butterworth, E. Ciapala, F. Dubouchet, J. Esteban Muller, D.C. Glenat, G. Hagmann, W. Höfle, D. Jacquet, M. Jaussi, S. Kouzue, D. Landre, J. Lollierou, P. Maesen, P. Martinez Yanez, T. Mastoridis, J.C. Molendijk, C. Nicou, J. Noirjean, G. Papotti, A.V. Pashnin, G. Pechaud, J. Pradier, J. Sanchez-Quesada, M. Schokker, E.N. Shaposhnikova, D. Stellfeld, J. Tückmantel, D. Valuch, U. Wehrle, F. Weierud
    CERN, Geneva, Switzerland
  
  The LHC RF system commissioning with beam and physics operation for 2010 and 2011 are presented. It became clear in early 2010 that RF noise was not a lifetime limiting factor: the crossing of the much feared 50 Hz line for the synchrotron frequency did not affect the beam. The broadband LHC RF noise is reduced to a level that makes its contribution to beam diffusion in physics well below that of Intra Beam Scattering. Capture losses are also under control, at well below 0.5%. Longitudinal emittance blow-up, needed for ramping of the nominal intensity single bunch, was rapidly commissioned. In 2011, 3.5 TeV/beam physics has been conducted with 1380 bunches at 50 ns spacing, corresponding to 55% of the nominal current. The intensity per bunch (1.3 ·1011 p) is significantly above the nominal 1.15 ·1011. By August 2011 the LHC has accumulated more than 2 fb-1 integrated luminosity, well in excess of the 1 fb-1 target for 2011.  
 
MOPC057 Loss of Landau Damping in the LHC emittance, injection, acceleration, impedance 211
 
  • E.N. Shaposhnikova, T. Argyropoulos, P. Baudrenghien, T. Bohl, A.C. Butterworth, J. Esteban Muller, T. Mastoridis, G. Papotti, J. Tückmantel, W. Venturini Delsolaro, U. Wehrle
    CERN, Geneva, Switzerland
  • C.M. Bhat
    Fermilab, Batavia, USA
  
  Loss of Landau damping leading to a single bunch longitudinal quadrupole instability has been observed in the LHC during the ramp and on the 3.5 TeV flat top for small injected longitudinal emittances. The first measurements are in good agreement with the threshold calculated for the expected longitudinal reactive impedance budget of the LHC as well as with the threshold dependence on beam energy. The cure is a controlled longitudinal emittance blow-up during the ramp which for constant threshold through the cycle should provide an emittance proportional to the square root of energy.  
 
MOPC072 Design of an RF Feed System for Standing-wave Accelerator Structures cavity, coupling, wakefield, linac 244
 
  • J. Neilson, V.A. Dolgashev, S.G. Tantawi
    SLAC, Menlo Park, California, USA
  
  Travelling wave (TW) accelerator structures are known to suffer from several deficiencies. A breakdown in one of the cells propagates towards the source. This results in damage to upstream cells in addition to the cell where the breakdown was initiated. The deficiencies of TW accelerator structures can be overcome by using standing wave (SW) cells that are fed in parallel. An RF breakdown is contained to the cell where it originates. This eliminates upstream cell damage and the resulting changes in phase shift between cells. In addition the feed structure can provide a high conductance port for vacuum pumping. We have completed the design of a parallel fed SW structure with a directional coupler for each cell and serpentine waveguide connection between couplers. This design approach improves isolation between the cells resulting in the maximum increase in the operational robustness of the accelerator structure. The design uses four feed arms spaced uniformly around the cell circumference to suppress dipole modes and improve damping of low order wakefields. Construction of a test structure in now underway and is scheduled for testing in October of this year.  
 
MOPC107 HOM and FP Coupler Design for the NLSF High Gradient SC Cavity cavity, HOM, simulation, SRF 325
 
  • R.M. Jones, N. Juntong
    UMAN, Manchester, United Kingdom
  
  The design of both higher order mode (HOM) and fundamental power (FP) couplers for the New Low Surface Field (NLSF) cavity* is presented. Here we study using the ILC baseline couplers for this new superconducting cavity. A Balleyguier method** of calculating external quality factor is used and the results validated using both Microwave studio and HFSS.
* N. Juntong and R.M. Jones, SRF2009, THPPO024, 2009.
** P. Balleyguier, LINAC98, MO4037, 1998
 		 
 
MOPC113 Results of Cavity Series Fabrication at Jefferson Laboratory for the Cryomodule “R100” cavity, cryomodule, HOM, target 340
 
  • F. Marhauser, W.A. Clemens, M.A. Drury, D. Forehand, J. Henry, S. Manning, R.B. Overton, R.S. Williams
    JLAB, Newport News, Virginia, USA
  
  Funding: Authored by Jefferson Science Associates, LLC under U.S. DOE Contract No. DE-AC05-06OR23177.
A series production of eight superconducting RF cavities for the cryomodule R100 was conducted at JLab in 2010. The cavities underwent chemical post-processing prior to vertical high power testing and routinely exceeded the envisaged performance specifications. After cryomodule assembly, cavities were successfully high power acceptance tested. In this paper, we present the achievements paving the way for the first demonstration of 100 MV (and beyond) in a single cryomodule to be operated at CEBAF. 		 
 
MOPO003 A Broadband RF Stripline Kicker for Damping Transversal Multibunch Instabilities kicker, impedance, feedback, single-bunch 481
 
  • M. Schedler, D. Heiliger, W. Hillert, A. Roth
    ELSA, Bonn, Germany
  
  When operating an RF feedback system, being able to reliably act upon every single bunch is a necessity. By employing a broadband RF stripline kicker, any bunch displacement can be corrected for. In a 500 MHz accelerator, the decay time of the electromagnetic field inside the kicker has to be less than 2 ns in order to avoid the following bunch to be affected. By designing the kicker as an RF coax device matched to the line impedance of the power cables, perturbing reflected signals are avoided. Additionally, the kicking strength and thus the shunt impedance should be maximized over the full spectrum from DC to 250 MHz. The kicker design has been optimized to meet the above requirements by relying on CST Microwave Studio simulations. Their results and first measurements are presented.  
 
MOPO012 LHC Damper Beam Commissioning in 2010 feedback, injection, kicker, ion 505
 
  • W. Höfle, G. Kotzian, M. Schokker, D. Valuch
    CERN, Geneva, Switzerland
  
  The LHC transverse dampers were commissioned in 2010 with beam and their use at injection energy of 450 GeV, during the ramp and in collisions at 3.5 TeV for Physics have become part of the standard operations procedure. The system proved important to limit emittance blow-up at injection and maintain smaller than nominal emittances throughout the accelerating cycle. We describe the commissioning of the system step-by-step as done in 2010 and summarize its performance as achieved for proton as well as ion beams in 2010. Although its principle function is to keep transverse oscillations under control, the system has also been used as an exciter for abort gap cleaning and tune measurement. The dedicated beam position measurement system with its low noise properties provides additional possibilities for diagnostics.  
 
MOPO027 Status of a Study of Stabilization and Fine Positioning of CLIC Quadrupoles to the Nanometre Level* quadrupole, feedback, alignment, controls 538
 
  • K. Artoos, C.G.R.L. Collette, M. Esposito, P. Fernandez Carmona, M. Guinchard, C. Hauviller, S.M. Janssens, A.M. Kuzmin, R. Leuxe, R. Moron Ballester
    CERN, Geneva, Switzerland
  
  Funding: The research leading to these results has received funding from the European Commission under the FP7 Research Infrastructures project EuCARD, grant agreement no.227579
Mechanical stability to the nanometre and below is required for the CLIC quadrupoles to frequencies as low as 1 Hz. An active stabilization and positioning system based on very stiff piezo electric actuators and inertial reference masses is under study for the Main Beam Quadrupoles (MBQ). The stiff support was selected for robustness against direct forces and for the option of incrementally repositioning the magnet with nanometre resolution. The technical feasibility was demonstrated by a representative test mass being stabilized and repositioned to the required level in the vertical and lateral direction. Technical issues were identified and the development programme of the support, sensors, and controller was continued to increase the performance, integrate the system in the overall controller, adapt to the accelerator environment, and reduce costs. The improvements are implemented in models, test benches, and design of the first stabilized prototype CLIC magnet. The characterization of vibration sources was extended to forces acting directly on the magnet, such as water-cooling induced vibrations. This paper shows the achievements, improvements, and an outlook on further R&D. 		 
 
MOPO028 Modal Analysis and Measurement of Water Cooling Induced Vibrations on a CLIC Main Beam Quadrupole Prototype* quadrupole, ground-motion, resonance, controls 541
 
  • K. Artoos, C.G.R.L. Collette, M. Esposito, P. Fernandez Carmona, M. Guinchard, S.M. Janssens, R. Leuxe, M. Modena, R. Moron Ballester, M. Struik
    CERN, Geneva, Switzerland
  • G. Deleglise, A. Jeremie
    IN2P3-LAPP, Annecy-le-Vieux, France
  
  Funding: The research leading to these results has received funding from the European Commission under the FP7 Research Infrastructures project EuCARD, grant agreement no. 227579.
To reach the Compact Linear Collider (CLIC) design luminosity, the mechanical jitter of the CLIC main beam quadrupoles should be smaller than 1.5 nm integrated root mean square (r.m.s.) displacement above 1 Hz. A stiff stabilization and nano-positioning system is being developed but the design and effectiveness of such a system will greatly depend on the stiffness of the quadrupole magnet which should be as high as possible. Modal vibration measurements were therefore performed on a first assembled prototype magnet to evaluate the different mechanical modes and their frequencies. The results were then compared with a Finite Element (FE) model. The vibrations induced by water-cooling without stabilization were measured with different flow rates. This paper describes and analyzes the measurement results. 		 
 
MOPS007 Interference of CSR Fields in a Curved Waveguide impedance, positron, storage-ring, wakefield 604
 
  • D.M. Zhou, K. Ohmi
    KEK, Ibaraki, Japan
  
  CSR fields generated by a bunched beam passing through a series of bending magnets may interfere with each other due the reflections of outer chamber wall. This kind of multi-bend interference causes sharp peaks and long-range tail in the CSR impedance and wake potentials, respectively. Using a dedicated computer code, CSRZ, we calculated the longitudinal CSR impedance in the SuperKEKB positron damping ring for purpose of demonstration. It was found that multi-bend interference may enhance the CSR fields within a distance comparable to the bunch length, which is typically in the order of several millimeters. A simple instability analysis was performed and it suggested that multi-bend interference might play a role in the single-bunch instabilities of small electron/positron rings.  
 
MOPS010 Experimental Studies with Low Transition Energy Optics in the SPS optics, emittance, injection, single-bunch 613
 
  • H. Bartosik, T. Argyropoulos, T. Bohl, S. Cettour Cave, K. Cornelis, J. Esteban Muller, Y. Papaphilippou, G. Rumolo, B. Salvant, E.N. Shaposhnikova, J. Wenninger
    CERN, Geneva, Switzerland
  
  The optics of the SPS can be tuned to lower transition energy such that the slippage factor at injection is raised by a factor of almost 3. From theory, an increase of the intensity thresholds for transverse mode coupling, longitudinal coupled bunch and longitudinal instabilities due to the loss of Landau damping can be expected. In this paper, experimental studies in the SPS with single bunches of protons with intensities of up to 3.5·1011 p/b on the flat bottom and at 450 GeV/c are presented. Longitudinal instabilities were studied with LHC-type beams with 50~ns spacing and injected intensities up to 1.8·1011 p/b. The measurements address the increase of intensity thresholds and the achievable transverse emittances in the new low gamma transition optics with respect to the nominal SPS optics. The obtained results are compared with numerical simulations.  
 
MOPS046 Impedances and Wakes in Round Three-layer Ceramic Waveguide impedance, acceleration, radiation, accumulation 703
 
  • M. Ivanyan, A.V. Tsakanian
    CANDLE, Yerevan, Armenia
  
  The round ceramic waveguide with inner and outer thin metal coating is considered. Using the exact methods the longitudinal impedances and potentials are calculated. Identification of the main patterns of changes in their properties by varying the electrodynamic and geometric parameters of the waveguide is performed as well. The possibility of optimizing the parameters of the waveguide for the effective implementation of two-beam acceleration is discussed.  
 
MOPS066 Collective Effects in the MAX IV 3 GeV Ring impedance, cavity, storage-ring, synchrotron 754
 
  • P.F. Tavares
    MAX-lab, Lund, Sweden
  • T.F. Günzel
    CELLS-ALBA Synchrotron, Cerdanyola del Vallès, Spain
  • R. Nagaoka
    SOLEIL, Gif-sur-Yvette, France
  
  We present calculations of collective instability effects in the 3 GeV electron storage ring of the MAX IV facility currently under construction in Lund, Sweden. The storage ring is designed to deliver ultra-low emittance down to 0.24 nm rad so as to provide high brightness synchrotron radiation from undulators. This is achieved in a comparatively small machine (528 m circumference) through the use of a multi-bend achromat lattice and a compact magnet design featuring multi-purpose narrow gap magnet blocks. This design features small dispersion leading to low momentum compaction, which, together with the small circular (11 mm radius) chambers, poses a challenge to reach the design current (500 mA in 176 bunches) without exciting instabilities and degrading beam parameters due to the interaction with the machine impedance. Particularly important are multi-bunch resistive wall effects in the NEG coated copper chamber as well single-bunch instabilities driven by the broad-band impedance. A low RF frequency (100 MHz) and harmonic cavities are foreseen to lengthen the bunches and increase instability thresholds.  
 
MOPS072 Broadband Electromagnetic Characterization of Materials for Accelerator Components impedance, simulation, kicker, RF-structure 769
 
  • C. Zannini, A. Grudiev, E. Métral, T. Pieloni, G. Rumolo
    CERN, Geneva, Switzerland
  • G. De Michele
    PSI, Villigen, Switzerland
  • C. Zannini
    EPFL, Lausanne, Switzerland
  
  Electromagnetic (EM) characterization of materials up to high frequencies is a major requirement for the correct modeling of many accelerator components: collimators, kickers, high order modes damping devices for accelerating cavities. In this scenario, the coaxial line method has gained much importance compared to other methods because of its applicability in a wide range of frequencies. In this paper we describe a new coaxial line method that allows using only one measurement setup to characterize the material in a range of frequency from few MHz up to several GHz. A coaxial cable fed at one side is filled with the material under test and closed on a known load on the other side. The properties of the material are obtained from the measured reflection coefficient by using it as input for a transmission line (TL) model or for 3D EM simulations, which describe the measurements setup. We have applied this method to characterize samples of SiC (Silicon Carbide) which could be used for LHC collimators and for CLIC accelerating structures and NiZn ferrite used for kicker magnets.  
 
MOPS084 Status of Electron Cloud Dynamics Measurements at CESRTA* dipole, electron, betatron, feedback 799
 
  • M.G. Billing, G. Dugan, M.J. Forster, D.L. Kreinick, R.E. Meller, M.A. Palmer, G. Ramirez, M.C. Rendina, N.T. Rider, J.P. Sikora, K.G. Sonnad, H.A. Williams
    CLASSE, Ithaca, New York, USA
  • J.Y. Chu
    CMU, Pittsburgh, Pennsylvania, USA
  • J.W. Flanagan
    KEK, Ibaraki, Japan
  • R. Holtzapple, M. Randazzo
    CalPoly, San Luis Obispo, California, USA
  
  Funding: Supported by US National Science Foundation (PHY-0734867) & Dept. of Energy (DE-FC02-08ER41538)
The study of electron cloud-related instabilities for the CESR-TA project permits the observation of the interaction of the electron cloud with the stored beam under a variety of accelerator conditions. These measurements are undertaken utilizing automatic and semi-automatic techniques for three basic observations: the measurement of tune shifts of individual bunches along a train, the detection of the coherent self-excited spectrum for each bunch within a train and the pulsed excitation of either the betatron dipole or head-tail mode for each individual bunch within the train, followed by the observation of the damping of its coherent motion. These techniques are employed to study the electron cloud-related interactions in a number of conditions, such as trains of bunches with low emittance and spaced by as little as 4 nsec between bunches. We report on the most recent observations and results. 		 
 
TUYB02 The Challenges of Ultra-low Emittance Damping Rings emittance, electron, quadrupole, coupling 956
 
  • D. L. Rubin
    CLASSE, Ithaca, New York, USA
  
  Funding: Work supported by the National Science Foundation and by the US Department of Energy under contract numbers PHY-0734867 and DE-FC02-08ER41538.
In this paper we review the state of the art of the design of damping rings for linear colliders, as supported by the experimental data from ATF and CESR test damping rings. We consider implications of measurements of electron cloud dynamics and mitigation in a radiation dominated ring. The techniques developed for tuning for ultra-low emittance in these rings are summarized. Other dynamics manifested in the ultra-low emittance regime where collective effects are important are discussed. 		 
slides icon Slides TUYB02 [7.198 MB]  
 
TUYB03 CLIC Conceptual Design and CTF3 Results linac, emittance, target, luminosity 961
 
  • D. Schulte
    CERN, Geneva, Switzerland
  
  An international collaboration is carrying out an extensive R&D programme to prepare CLIC, a multi-TeV electron-positron collider. In this concept, the colliding beams will be accelerated in very high gradient normal conducting 12 GHz accelerating structures. The necessary RF power is extracted from a high-current, low-energy drive beam that runs parallel to the colliding beams and is generated in a central complex. This year the collaboration will produce a conceptual design report to establish the feasibility of the technology. The CLIC concept will be introduced and the status of key studies of critical issues will be reviewed. A focus will be on the CLIC Test Facility 3 (CTF3), which is a test facility to produce and use high current a drive beam.  
slides icon Slides TUYB03 [13.204 MB]  
 
TUPC011 Striplines for CLIC Pre-Damping and Damping Rings* impedance, kicker, vacuum, extraction 1012
 
  • C. Belver-Aguilar, A. Faus-Golfe
    IFIC, Valencia, Spain
  • M.J. Barnes, G. Rumolo
    CERN, Geneva, Switzerland
  • F. Toral
    CIEMAT, Madrid, Spain
  • C. Zannini
    EPFL, Lausanne, Switzerland
  
  The Compact Linear Collider (CLIC) study explores the scheme for an electron-positron collider with high luminosity and a nominal center-of-mass energy of 3 TeV: CLIC would complement LHC physics in the multi-TeV range. The CLIC design relies on the presence of Pre-Damping Rings (PDR) and Damping Rings (DR) to achieve, through synchrotron radiation, the very low emittance needed to fulfil the luminosity requirements. The specifications for the kicker systems are very challenging and include very low beam coupling impedance and excellent field homogeneity: striplines have been chosen for the kicker elements. Analytical calculations have been carried out to determine the effect of tapering upon the high frequency beam coupling impedance. In addition detailed numerical modeling of the field homogeneity has been performed and the sensitivity of the homogeneity to various parameters, including stripline cross-section, has been studied. This paper presents the main conclusions of the beam impedance calculations and field homogeneity predictions.  
 
TUPC015 Comparative Wakefield Analysis of a First Prototype of a DDS Structure for CLIC Main Linac wakefield, simulation, impedance, dipole 1024
 
  • A. D'Elia, A. Grudiev, V.F. Khan, W. Wuensch
    CERN, Geneva, Switzerland
  • R.M. Jones
    UMAN, Manchester, United Kingdom
  
  A Damped Detuned Structure (DDS) for CLIC main linac has been proposed as an alternative to the present baseline design which is based on heavy damping. A first prototype, CLICDDSA, for high power tests has been already designed and is under construction. It is also foreseen to design a further prototype, CLICDDSB, to test both the wakefield suppression and high power performances. Wakefield calculations for DDS are, in the early design stage, based on single infinitely periodic cells. Though cell-to-cell interaction is taken into account to calculate the wakefields, it is important to study full structure properties using computational tools. In particular this is fundamental for defining the input parameters for the HOM coupler that is crucial for the performances of DDS. In the following a full analysis of wakefields and impedances based on simulations conducted with finite difference based electromagnetic computer code GdfidL will be presented.  
 
TUPC026 Status of the Crab Cavity Design for the CLIC cavity, wakefield, dipole, coupling 1054
 
  • P.K. Ambattu, G. Burt, A.C. Dexter
    Cockcroft Institute, Lancaster University, Lancaster, United Kingdom
  • V.A. Dolgashev
    SLAC, Menlo Park, California, USA
  • A. Grudiev
    CERN, Geneva, Switzerland
  • R.M. Jones
    UMAN, Manchester, United Kingdom
  • P.A. McIntosh
    STFC/DL/ASTeC, Daresbury, Warrington, Cheshire, United Kingdom
  
  RF design of a crab cavity (2π/3, 11.9942 GHz) for the Compact Linear Collide (CLIC) is presented. As part of the UK-CLIC collaboration, CERN is building two copper prototypes, designed by Lancaster University / Cockcroft Institute. The first prototype to be made will be a 12 cell undamped cavity and the second will be waveguide damped cavity. The RF test at CERN will help characterisation of the dipole mode with X-band RF pulses of 15 MW peak power and pulse length of ~242 ns. Since the cavity frequency and phase advance per cell are identical to those of the CLIC main linac, the first prototype could exploit CERN’s X-band cavity characterisation facilities. A fully damped cavity will be required for the actual machine in order to meet the luminosity specs. The damped prototype will use an identical coupler type as the undamped one, but the cells will have damping waveguides with / without dielectric material.  
 
TUPC049 Optics considerations for the Delay Loop in the CLIC Damping Rings Complex dipole, quadrupole, emittance, optics 1108
 
  • P. Zisopoulos, F. Antoniou, H. Bartosik, Y. Papaphilippou
    CERN, Geneva, Switzerland
  
  For the recombination of the two trains coming from the CLIC damping rings, a delay loop will be used in order to obtain the nominal 0.5~ns bunch spacing. The optics design of the loop is based upon an isochronous ring, in order to preserve the longitudinal beam distribution. Analytical expressions for achieving isochronous conditions in high order for Theoretical Minimum Emittance cells are obtained. A parametrisation of the quadrupole settings for achieving these conditions is presented, along with general considerations regarding the choice of bending magnet characteristics.  
 
TUPC050 Impedance Effects in the CLIC Damping Rings impedance, wiggler, simulation, vacuum 1111
 
  • E. Koukovini, K.S.B. Li, N. Mounet, G. Rumolo, B. Salvant
    CERN, Geneva, Switzerland
  
  Due to the unprecedented brilliance of the beams, the performance of the Compact Linear Collider (CLIC) damping rings is affected by collective effects. Single bunch instability thresholds based on a broad-band resonator model and the associated coherent tune shifts have been evaluated with the HEADTAIL code. Simulations performed for positive and negative values of chromaticity proved that higher order bunch modes can be potentially dangerous for the beam stability. This study also includes the effects of high frequency resistive wall impedance due to different coatings applied on the chambers of the wigglers for e-cloud mitigation and/or ultra-low vacuum pressure. The impact of the resistive-wall wake fields on the transverse impedance budget is finally discussed.  
 
TUPC053 Superconducting Positron Stacking Ring for CLIC positron, injection, synchrotron, septum 1117
 
  • F. Zimmermann, L. Rinolfi
    CERN, Geneva, Switzerland
  • E.V. Bulyak, P. Gladkikh
    NSC/KIPT, Kharkov, Ukraine
  • T. Omori, J. Urakawa, K. Yokoya
    KEK, Ibaraki, Japan
  
  The generation of polarized positrons for future colliders based on Compton storage rings is a promising method. A challenging key ingredient of this method is the necessary quasi-continuous positron injection into a stacking ring. The ordinary methods of multi-turn injection are not appropriate for this purpose, because the required number of injection-turns is a few hundred, and the emittance of the injected positron bunches is large. This paper describes a possible solution based on 5 GeV superconducting stacking ring, where a novel method of the combined longitudinal and transverse injection process is used to stack positrons. The ring dynamic aperture allows to inject the positron beam with normalized emittance up to 2000 micrometers during a few hundred turns. The injection efficiency is larger than 90% in simulation. The number of the injection turns is only limited by the synchrotron radiation power. The ring lattice and the results of injection simulations are presented.  
 
TUPC157 Design and Initial Results of a Turn-by-Turn Beam Position Monitoring System for Multiple Bunch Operation of the ATF Damping Ring injection, single-bunch, feedback, extraction 1398
 
  • G.B. Christian, D.R. Bett, M.R. Davis, C. Perry
    JAI, Oxford, United Kingdom
  • R. Apsimon, P. Burrows
    Oxford University, Physics Department, Oxford, Oxon, United Kingdom
  • B. Constance, A. Gerbershagen
    CERN, Geneva, Switzerland
  • J. Resta-López
    IFIC, Valencia, Spain
  
  An FPGA-based monitoring system has been developed to study multi-bunch beam instabilities in the damping ring (DR) of the KEK Accelerator Test Facility (ATF), utilising a stripline beam position monitor (BPM) and existing BPM processor hardware. The system is designed to record the horizontal and/or vertical positions of up to three bunches in the DR in single-bunch multi-train mode or the head bunch of up to three trains in multi-bunch mode, with a bunch spacing of 5.6 ns. The FPGA firmware and data acquisition software were modified to record turn-by-turn data for up to six channels and 1–3 bunches in the DR. An overview of the system and initial results will be presented.  
 
TUPC170 Resonant TE Wave Measurements of Electron Cloud Densities at CesrTA cavity, resonance, electron, plasma 1434
 
  • J.P. Sikora, M.G. Billing, M.A. Palmer, K.G. Sonnad
    CLASSE, Ithaca, New York, USA
  • B.T. Carlson
    CMU, Pittsburgh, Pennsylvania, USA
  • S. De Santis
    LBNL, Berkeley, California, USA
  • K.C. Hammond
    Harvard University, Cambridge, Massachusetts, USA
  
  Funding: This work is supported by the US National Science Foundation PHY-0734867, and the US Department of Energy DE-FC02-08ER41538.
The Cornell Electron Storage Ring has been reconfigured as a test accelerator (CesrTA). Measurements of electron cloud densities have been made at CesrTA using the TE Wave transmission technique. However, interpretation of the data based on single pass transmission is problematic because of the reflections and standing waves produced by discontinuities in the beam pipe - from pumps, bellows, etc. that are normally present in an accelerator vacuum chamber. An alternative model is that of a resonant cavity, formed by the beampipe and its discontinuities. The theory for the measurement of plasma densities in cavities is well established. This paper will apply this theory to electron cloud measurements, present some simplified measurements on waveguide, and apply this model to the interpretation of some of the data taken at CesrTA. 		 
 
TUPO002 High Flux Polarized Gamma Rays Production: First Measurements with a Four-mirror Cavity at the ATF laser, cavity, electron, positron 1446
 
  • N. Delerue, J. Bonis, I. Chaikovska, R. Chiche, R. Cizeron, M. Cohen, P. Cornebise, R. Flaminio, D. Jehanno, F. Labaye, M. Lacroix, Y. Peinaud, L. Pinard, V. Soskov, A. Variola, Z.F. Zomer
    LAL, Orsay, France
  • T. Akagi, S. Miyoshi
    Hiroshima University, Graduate School of Advanced Sciences of Matter, Higashi-Hiroshima, Japan
  • S. Araki, Y. Funahashi, Y. Honda, T. Omori, H. Shimizu, N. Terunuma, J. Urakawa
    KEK, Ibaraki, Japan
  • E. Cormier
    CELIA, Talence, France
  • T. Takahashi
    Hiroshima University, Graduate School of Science, Higashi-Hiroshima, Japan
  
  Funding: ANR, IN2P3
The next generation of e+/e- colliders will require the production of a very intense flux of gamma rays to allow polarized positrons to be produced in sufficient quantities. To demonstrate that this can be achieved a four-mirror cavity has recently been installed at the Accelerator Test Facility (ATF) at KEK to produce a high flux of polarized gamma rays by inverse Compton scattering. A four-mirror non-planar geometry is used to ensure the polarization of the gamma rays produced. The main mechanical features of the cavity are presented. A fibre amplifier is used to inject about 10W in the high finesse cavity with a gain of 1000. A digital feedback system is used to keep the cavity at the length required for the optimal power enhancement. First preliminary measurements show that on some beam crossings the interactions produce more than 25 photons with an average energy of about 24 MeV. Several upgrades currently in progress are described. 		 
 
TUPO017 Peculiarities of the Excitation of an Optical Resonator by an Electron Beam electron, undulator, radiation, storage-ring 1479
 
  • E.G. Bessonov, M.V. Gorbunkov, A.L. Osipov
    LPI, Moscow, Russia
  • A.A. Mikhailichenko
    CLASSE, Ithaca, New York, USA
  
  The peculiarities of the optical resonator excitation by electrons in a FEL based on the Self-Stimulated Undulator Radiation at main and collateral synchronicity conditions are discussed*.
* E.G.Bessonov et al., Self-Stimulated Undulator Radiation and its Possible Applications, http://arxiv.org/ftp/arxiv/papers/1009/1009.3724.pdf 		 
 
TUPS021 Simulations and Vacuum Tests of a CLIC Accelerating Structure vacuum, simulation, cavity, ion 1569
 
  • C. Garion
    CERN, Geneva, Switzerland
  
  The Compact LInear Collider, under study, is based on room temperature high gradient structures. The vacuum specificities of these cavities are low conductance, large surface areas and a non-baked system. The main issue is to reach UHV conditions (typically 10-7 Pa) in a system where the residual vacuum is driven by water outgassing. A finite element model based on an analogy thermal/vacuum has been built to estimate the vacuum profile in an accelerating structure. Vacuum tests are carried out in a dedicated set-up, the vacuum performances of different configurations are presented and compared with the predictions.  
 
TUPS055 Organizing the ILC Technical Design Documentation lattice, positron, linear-collider, collider 1656
 
  • L. Hagge, S. Eucker, B. List, N.J. Walker, N. Welle
    DESY, Hamburg, Germany
  
  The Global Design Effort (GDE) for the International Linear Collider (ILC) is currently preparing the Technical Design Report (TDR), which will be released at the end of 2012 and will serve as the basis for a decision process. The TDR will be written based on the Technical Design Documentation (TDD), which captures the entire design efforts, results and rationale, including e. g. parameter lists, specifications, CAD models and drawings, cost estimation, simulations and calculations, and summary reports. Formal review meetings help making the documentation complete, correct and consistent. The TDD is stored in an Engineering Data Management System (EDMS), which ensures that it remains accessible beyond the GDE in an organized way and at a well-defined location. The EDMS provides traceability (e. g. from design decisions to corresponding cost estimates), version management and change control. The poster presents the process and tools that were established for the organization of the TDD and provides an overview of the emerging documentation.  
 
TUPS098 Machining and Characterizing X-band RF-structures for CLIC controls, cavity, collider, electron 1768
 
  • S. Atieh, M. Aicheler, G. Arnau-Izquierdo, A. Cherif, L. Deparis, D. Glaude, L. Remandet, G. Riddone, M. Scheubel
    CERN, Geneva, Switzerland
  • D. Gudkov, A. Samoshkin, A. Solodko
    JINR, Dubna, Moscow Region, Russia
  
  The Compact Linear Collider (CLIC) is currently under study at CERN as a potential multi-TeV e+e– collider. The manufacturing and assembling tolerances for making the required RF components are essential for CLIC to perform efficiently. Machining techniques are relevant to the construction of ultra-high-precision parts for the Accelerating Structures (AS). Optical-quality turning and ultra-precision milling using diamond tools are the main manufacturing techniques identified to produce ultra-high shape accuracy parts. A shape error of less than 5 micrometres and roughness of Ra 0.025 are achieved. Scanning Electron Microscopy (SEM) observation as well as sub-micron precision Coordinate Measuring Machines (CMM), roughness measurements and their crucial environment were implemented at CERN for quality assurance and further development. This paper focuses on the enhancements of precision machining and characterizing the fabrication of AS parts.  
 
TUPS099 A Study of the Surface Quality of High Purity Copper after Heat Treatment vacuum, electron, linear-collider, collider 1771
 
  • M. Aicheler, G. Arnau-Izquierdo, S. Atieh, S. Calatroni, S. Lebet, G. Riddone, A. Samoshkin
    CERN, Geneva, Switzerland
  
  The manufacturing flow of accelerating structures for the compact linear collider, based on diamond-machined high purity copper components, include several thermal cycles (diffusion bonding, brazing of cooling circuits, baking in vacuum, etc.). The high temperature cycles may be carried out following different schedules and environments (vacuum, reducing hydrogen atmosphere, argon, etc.) and develop peculiar surface topographies which have been the object of extended observations. This study presents and discusses the results of scanning electron microscopy (SEM) and optical microscopy investigations.  
 
TUPS106 Absorber Materials at Room and Cryogenic Temperatures* HOM, cavity, cryogenics, electron 1792
 
  • F. Marhauser, T.S. Elliott, A.T. Wu
    JLAB, Newport News, Virginia, USA
  • E.P. Chojnacki
    CLASSE, Ithaca, New York, USA
  • E. Savrun
    Sienna Technologies Inc., Woodinville, USA
  
  Funding: Authored by Jefferson Science Associates, LLC under U.S. DOE Contract No. DE-AC05-06OR23177.
We recently reported on investigations of RF absorber materials at cryogenic temperatures conducted at Jefferson Laboratory (JLab). The work was initiated to find a replacement material for the 2 Kelvin low power waveguide Higher Order Mode (HOM) absorbers employed within the original cavity cryomodules of the Continuous Electron Beam Accelerator Facility (CEBAF). This effort eventually led to suitable candidates as reported in this paper. Furthermore, though constrained by small funds for labor and resources, we have analyzed a variety of lossy ceramic materials, several of which could be usable as HOM absorbers for both normal conducting and superconducting RF structures, e.g. as loads in cavity waveguides and beam tubes either at room or cryogenic temperatures and, depending on cooling measures, low to high operational power levels. 		 
 
TUPZ010 Longitudinal Emittance Blow-up in the LHC emittance, synchrotron, feedback, acceleration 1819
 
  • P. Baudrenghien, A.C. Butterworth, M. Jaussi, T. Mastoridis, G. Papotti, E.N. Shaposhnikova, J. Tückmantel
    CERN, Geneva, Switzerland
  
  The LHC relies on Landau damping for longitudinal stability. To avoid decreasing the stability margin at high energy, the longitudinal emittance must be continuously increased during the acceleration ramp. Longitudinal blow-up provides the required emittance growth. The method was implemented through the summer of 2010. We inject band-limited RF phase-noise in the main accelerating cavities during the whole ramp of about 11 minutes. Synchrotron frequencies change along the energy ramp, but the digitally created noise tracks the frequency change. The position of the noise-band, relative to the nominal synchrotron frequency, and the bandwidth of the spectrum are set by pre-defined constants, making the diffusion stop at the edges of the demanded distribution. The noise amplitude is controlled by feedback using the measurement of the average bunch length. This algorithm reproducibly achieves the programmed bunch length of about 1.2 ns (4 σ) at flat top with low bunch-to-bunch scatter and provides a stable beam for physics coast.  
 
TUPZ014 Luminosity Optimization for a Higher-Energy LHC emittance, luminosity, radiation, proton 1831
 
  • C.O. Domínguez, F. Zimmermann
    CERN, Geneva, Switzerland
  
  A Higher-Energy Large Hadron Collider (HE-LHC) is an option to further push the energy frontier of particle physics beyond the present LHC. A beam energy of 16.5 TeV would require 20-T dipole magnets in the existing LHC tunnel, which should be compared with 7 TeV and 8.33 T for the nominal LHC. Since the synchrotron radiation power increases with the fourth power of the energy, radiation damping becomes significant for the HE-LHC. It calls for transverse and longitudinal emittance control vis-à-vis beam-beam interaction and Landau damping. The heat load from synchrotron radiation, gas scattering, and electron cloud also increases with respect to the LHC. In this paper we discuss the proposed HE-LHC beam parameters; the time evolution of luminosity, beam-beam tune shifts, and emittances during an HE-LHC store; the expected heat load; and luminosity optimization schemes for both round and flat beams.  
 
TUPZ022 Longitudinal Beam Measurements at the LHC: The LHC Beam Quality Monitor injection, pick-up, controls, emittance 1852
 
  • G. Papotti, T. Bohl, F. Follin, U. Wehrle
    CERN, Geneva, Switzerland
  
  The LHC Beam Quality Monitor is a system that measures individual bunch lengths and positions, similarly to the twin system SPS Beam Quality Monitor, from which it was derived. The pattern verification that the system provides is vital during the injection process to verify the correctness of the injected pattern, while the bunch length measurement is fedback to control the longitudinal emittance blow up performed during the energy ramp. In 2010 the system could for example clearly detect instances of longitudinal instabilities and beam excitation due to excess RF noise. The algorithms used, the hardware implementation and the system integration in the LHC control infrastructure are presented in this paper, along with possible improvements.  
 
TUPZ029 Observation of Coherent Beam-beam Effects in the LHC simulation, emittance, beam-beam-effects, collider 1870
 
  • X. Buffat
    EPFL, Lausanne, Switzerland
  • R. Calaga, S.M. White
    BNL, Upton, Long Island, New York, USA
  • R. Giachino, W. Herr, G. Papotti, T. Pieloni
    CERN, Geneva, Switzerland
  
  Early collisions in the LHC with a very limited number of bunches with high intensities indicated the presence of coherent beam-beam driven oscillations. Here we discuss the experimental results and compare with the expectations.  
 
WEPC049 Operation and Storage Ring Calibration with the Transverse Bunch-by-Bunch Feedback System at the Australian Synchrotron feedback, sextupole, synchrotron, storage-ring 2121
 
  • M.J. Boland, Y.E. Tan
    ASCo, Clayton, Victoria, Australia
  • D.J. Peake, R.P. Rassool, K.P. Wootton
    The University of Melbourne, Melbourne, Australia
  
  The first operational experience with the transverse bunch-by-bunch feedback system for the storage ring shows a doubling of the lifetime and the ability to damp instabilities caused by IVU gap changes. The system was also used to calibrate the ring by doing simultaneous measurements on several single bunches with different bunch currents. Using the bunch-by-bunch system's capability to excite the beam to large amplitudes, the non-linear beam dynamics were also measured and compared with the model.  
 
WEPC051 Effect of Compton Scattering on the Electron Beam Dynamics at the ATF Damping Ring electron, scattering, laser, cavity 2127
 
  • I. Chaikovska, C. Bruni, N. Delerue, A. Variola, Z.F. Zomer
    LAL, Orsay, France
  • K. Kubo, T. Naito, T. Omori, N. Terunuma, J. Urakawa
    KEK, Ibaraki, Japan
  
  Compton scattering provides one of the most promising scheme to obtain polarized positrons for the next generation of e+e− colliders. Moreover it is an attractive method to produce monochromatic high energy polarized gammas for nuclear applications and X-rays for compact light sources. In this framework a four-mirror Fabry-Perot cavity has been installed at the Accelerator Test Facility (ATF - KEK, Tsukuba, Japan) and will be used to produce an intense flux of polarized gamma rays by Compton scattering. For electrons at the energy of the ATF (1.28GeV) Compton scattering may result in a shorter lifetime due to the limited bucket acceptance. We have implemented the effect of Compton scattering on a 2D tracking code with a Monte-Carlo method. This code has been used to study the longitudinal dynamics of the electron beam at the ATF damping ring, in particular the evolution of the energy spread and the bunch length under Compton scattering. The results obtained are presented and discussed. Possible methods to observe the effect of Compton scattering on the ATF beam are proposed.  
 
WEPC105 Multiparticle Simulation of Intrabeam Scattering for SuperB emittance, simulation, scattering, lattice 2259
 
  • T. Demma, M.E. Biagini, M. Boscolo
    INFN/LNF, Frascati (Roma), Italy
  • K.L.F. Bane, A. Chao, M.T.F. Pivi
    SLAC, Menlo Park, California, USA
  
  Intrabeam scattering (IBS) is associated with multiple small angle scattering events leading to emittance growth. In most electron storage rings, the growth rates arising from IBS are much longer than damping times due to synchrotron radiation, and the effect on emittance growth is negligible. However, IBS growth rates increase with increasing bunch charge density, and for storage rings such as SuperB, that operate with high bunch charges and very low vertical emittance, the IBS growth rates can be large enough to produce significant emittance increase. Several formalisms have been developed for calculating IBS growth rates in storage rings*. However these models, based on Gaussian bunch distributions, cannot investigate some interesting aspects of IBS such as its evolution during the damping process and its effect on the beam distribution. We developed a multiparticle tracking code, based on the Binary Collision Model**, to investigate these effects. In this communication we present the structure of the code and simulation results obtained with particular reference to the SuperB parameters. Simulation results are compared with those of conventional IBS theories.
* A. Piwinski, Lect. Notes Phys. 296 (1988); J.D. Bjorken and S.K. Mtingwa, Part. Accel. 13 (1983); K. Kubo et al., Phys. Rev. ST-AB 8 (2005).
** Peicheng Yu et al., Phys. Rev. ST–AB 12 (2009).
 		 
 
WEPS002 Limitations in Mitigating Collective Effects in the Beta-Beam Decay Ring by the Use of Octupoles octupole, ion, injection, impedance 2481
 
  • C. Hansen
    CERN, Geneva, Switzerland
  • E. Benedetto
    National Technical University of Athens, Zografou, Greece
  • A. Chancé, J. Payet
    CEA/DSM/IRFU, France
  
  Funding: I acknowledge the financial support of the European Community under the European Commission Framework Programme 7 Design Study: EUROnu, Project Number 212372.
The beta-beam concept relies on the production, by beta decay of radioactive ions of a very high flux, of an electron neutrino and anti-neutrino beam towards a distant detector. After production and acceleration in an accelerator complex consisting of a rapid cycling synchrotron, the CERN PS and the CERN SPS, the radioactive isotopes are injected into a long racetrack-shaped ring, called the decay ring, where they orbit until they decay or are lost. The required intensities to store in the decay ring to reach the aimed neutrino fluxes are very high. Among the collective effects, the head tail effect, caused by transversal resonance impedance, is one of the main issues: the beam was shown to be unstable with the previous decay ring lattice. The lattice was changed to handle this problem; e.g. octupoles were included to increase the stability limit with an amplitude detuning. We here report on the improvement on the beta-beam performance with respect to amplitude detuning in the decay ring and discuss other mitigation attempts. 		 
 
THPC158 Field Optimization for Short Period Undulators undulator, wiggler, permanent-magnet, insertion 3260
 
  • P. Peiffer, A. Bernhard
    KIT, Karlsruhe, Germany
  • R. Rossmanith
    Karlsruhe Institute of Technology (KIT), Karlsruhe, Germany
  • D. Schoerling
    CERN, Geneva, Switzerland
  
  Undulators dedicated to low energy electron beams, like Laser Wakefield Accelerators, require very short period lengths to achieve X-ray emission. However, at these short period lengths (~5 mm) it becomes difficult to reach magnetic field amplitudes that lead to a K parameter of ~1, which is generally desired. Room temperature permanent magnets and even superconductive undulators using Nb-Ti as conductor material have proven insufficient to achieve the desired field amplitudes. The superconductor Nb3Sn has the theoretical potential to achieve the desired fields. However, up to now it is limited by several technological challenges to much lower field values than theoretically predicted. Alternatives for higher fields would be to manufacture the poles of the undulator body from Holmium instead of iron or to use Nb-Ti wires with a higher superconductor/copper ratio. The advantages and challenges of the different options are compared in this contribution.  
 
THPO025 Longitudinal Beam Dynamics of a Laser Sliced Bunch laser, synchrotron, electron, radiation 3397
 
  • P. Kuske
    HZB, Berlin, Germany
  
  Nowadays fs-laser slicing of a bunch of electrons in storage rings is quite common for creating short VUV- and soft X-ray light pulses or pulses of coherently emitted THz-radiation over a couple of revolutions. In this paper the longitudinal dynamics of the sliced bunch is studied numerically. The calculations are based on the one dimensional solution of the Vlasov-Fokker-Planck-equation assuming that the shielded CSR-wake is dominating the dynamics of the 100 fs-long slice. It is found that the density modulation survives longer and that the CSR-spectra extend to higher frequencies at later turns even below the corresponding instability threshold. This very simple model seems to support experimental observations at the Swiss Light Source.  
 
THPO032 Preliminary Design of an Inductive Adder for CLIC Damping Rings kicker, emittance, collider, impedance 3409
 
  • J. Holma, M.J. Barnes
    CERN, Geneva, Switzerland
  
  The Compact Linear Collider (CLIC) study is exploring the scheme for an electron-positron collider with high luminosity and a nominal centre-of-mass energy of 3 TeV. The CLIC damping rings will produce ultra-low emittance, with high bunch charge, necessary for the luminosity performance of the collider. To limit the beam emittance blow-up due to oscillations, the pulse power modulators for the damping rings kickers must provide extremely flat, high-voltage pulses: specifications call for a 160 ns duration flattop of 12.5 kV, 250 A, with a combined ripple and droop of not more than ±0.02 %. A solid-state modulator, the inductive adder, is a very promising approach to meeting the demanding specifications; this topology allows the use of both digital and analogue modulation. To effectively use modulation techniques to achieve such low ripple and droop requires an in-depth knowledge of the behaviour of the solid-state switching components and their gate drivers, as well as a good understanding of the overall circuit behaviour. This paper describes the initial design of the inductive adder.  
 
THPZ021 Effect of Coherent Synchrotron Radiation at the SuperKEKB Damping Ring vacuum, emittance, linac, wakefield 3732
 
  • H. Ikeda, T. Abe, M. Kikuchi, K. Oide, K. Shibata, M. Tobiyama, D.M. Zhou
    KEK, Ibaraki, Japan
  
  The longitudinal wake field dominated by the CSR is important at the SuperKEKB damping ring. The peak of the CSR wake field is 100 times higher than those of the vacuum chamber components. We calculated the CSR effect for different vacuum chamber cross-sections, and adopted one which reduced longitudinal instability.