Keyword: wakefield
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MOPC012 Fabrication of the CERN/PSI/ST X-band Accelerating Structures alignment, vacuum, FEL, coupling 86
 
  • M.M. Dehler, A. Citterio, R. Zennaro
    PSI, Villigen, Switzerland
  • S. Atieh, D. Gudkov, S. Lebet, G. Riddone, J. Shi
    CERN, Geneva, Switzerland
  • G. D'Auria, C. Serpico
    ELETTRA, Basovizza, Italy
  
  Within a collaboration between CERN, PSI and Sincrotrone Trieste (ST), a multi- purpose X-band accelerating structure has been designed and fabricated, used for high gradients tests in the CLIC structure testing program and in the FEL projects of PSI and ST. The structure has 72 cells with a phase advance of 5 pi/6 and includes upstream and downstream wakefield monitors to measure the beam alignment. The SLAC mode launcher design is used to feed it with RF power. Following the CERN fabrication procedures for high-gradient structure, diffusion bonding and brazing in hydrogen atmosphere is used to assemble the cells. After tuning, a vacuum bakeout is required before the feedthroughs for the wake field monitors are welded in as a last step. We describe the experiences gained in finishing the first two structures out of a series of four and present the results from the RF tuning and low level RF tests.  
 
MOPC021 Design of a Choke-mode Damped Accelerating Structure for CLIC Main Linac damping, impedance, 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 damping, vacuum, alignment, controls 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, damping, 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.  
 
MOPC072 Design of an RF Feed System for Standing-wave Accelerator Structures cavity, coupling, damping, 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.  
 
MOPC144 Autocorrelation Function and Power Spectrum of a Train of Quasiperiodic Sequence of Pulses electron, FEL, free-electron-laser, optics 415
 
  • E.M. Laziev, B. Grigoryan, V.M. Tsakanov
    CANDLE, Yerevan, Armenia
  • M. Movsisyan, D.L. Oganesyan
    YSU, Yerevan, Armenia
  
  The statistical relationship of the autocorrelation function and spectrum of a train of quasi-periodic sequence of pulses having a time jitter of the repetition rate is obtained. Presented the accordance of autocorrelation function as well as power spectrum of the bounded quasi-periodic sequence of pulses and timing jitter of their repetition rate. The results can be used at the measurements of timing jitter of a train of electron bunches.  
 
MOPO007 Resonant Strip-line Type Longitudinal Kicker kicker, simulation, impedance, feedback 493
 
  • T. Nakamura
    JASRI/SPring-8, Hyogo-ken, Japan
  
  The longitudinal feedback for the SPring-8 storage ring is under consideration as the device for suppression of the longitudinal instabilities driven by higher order modes of cavities, observed at test operation with 4 to 6 GeV low energy beam. As the beam energy and the ring circumference are rather high, and the length of the space for the longitudinal kickers is limited, high efficiency kicker per length is required in the our case. As a candidate of such kicker, we propose a resonant strip-line type longitudinal kicker with drive frequency of 13/4 of RF frequency. The shut impedance per length is higher than over-loaded cavities and the drive circuits can be simplified because of higher drive frequency. The design consideration, the result of the simulation and measurement of the prototype model, and the detail of the drive circuit will be reported in the presentation.  
 
MOPS006 Beam Tilt due to Transverse Wakefields for DAΦNE, SuperB, KEKB and SuperKEKB impedance, closed-orbit, collider, vacuum 601
 
  • D.M. Zhou, K. Ohmi
    KEK, Ibaraki, Japan
  • A. Chao
    SLAC, Menlo Park, California, USA
  
  When a beam bunch traverses a transverse impedance, the bunch head generates a transverse wakefield that kicks the bunch tail, generating a betatron motion of the tail relative to the head. In a storage ring, in a steady state, this kick to the bunch tail produces a transverse closed orbit (e.g. in the y-direction) of the bunch tail relative to the bunch head, which means the beam now has a y-z tilt. Such beam tilt due to transverse wakefields may cause a loss of luminosity in storage ring colliders or loss of brightness in light sources. In this paper, we present a preliminary study of the beam tilt effect for the colliders DAΦNE, SuperB, KEKB and SuperKEKB.  
 
MOPS007 Interference of CSR Fields in a Curved Waveguide impedance, positron, damping, storage-ring 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.  
 
MOPS045 Coupling Impedance of Rough Resistive Pipe* impedance, coupling, resonance, vacuum 700
 
  • M. Ivanyan, V.M. Tsakanov
    CANDLE, Yerevan, Armenia
  
  A new version of modelling of the surface roughness impact by thin dielectric layer in the round resistive beam pipe is suggested. The calculation method of coupled resistive-roughness impedance is developed.  
 
MOPS058 KEKB Linac Wakefield Studies of Comparing Theoretical Calculation, Simulation and Experimental Measurement* emittance, linac, injection, simulation 739
 
  • L. Zang, N. Iida, Y. Ogawa, M. Satoh, M. Yoshida, D.M. Zhou
    KEK, Ibaraki, Japan
  
  For superKEKB, in order to achieve aiming luminosity machine need to run with a nano-beam scheme so that a small beam emittance is critical important. During the beam propagation, the short-range wake field in the accelerating structure will cause the beam instability and emittance growth. In practical, injecting beam with certain offset could compensate wakfield. And beam emittance could be measured by tuning the quadruple known as quadscan method. In this paper, wakefield theoretical calculation, simulation results will be presented. And then the wakefield impact to beam emittance and wakefield compensation will be discussed. Finally, we will show the comparison of the results getting from theoretical calculation and experimental measurement.  
 
MOPS060 Study on Resistive Wall Instability in CSNS/RCS simulation, injection, impedance, extraction 745
 
  • L. Huang, Y.D. Liu, S. Wang
    IHEP Beijing, Bejing, People's Republic of China
  
  Rapid Cycling Synchrotron of the China Spallation Neutron Source is a high intensity proton accelerator, with average beam power of 100kW. The collective effects caused by the coupling impedance may be the limit to beam power. The impedance estimation for components on beam line shows that the resistive wall impedance and its instability are more serious than any others. Based on the impedance budget, the instability is theoretically estimated. And a simple resistive wall wake field model is used to simulate the bunch oscillation and the growth rate instability. In this model, the continuous resistive wall wake field is equivalent to a point wake field and long bunch is sliced into many micro-bunches. By tracking the dynamics of the macro-bunches, the transverse growth rate are obtained and the result are analyzed.  
 
MOPS075 Simulation of Multibunch Motion with the HEADTAIL Code and Application to the CERN SPS and LHC impedance, simulation, synchrotron, coupling 778
 
  • N. Mounet
    EPFL, Lausanne, Switzerland
  • N. Mounet, E. Métral, G. Rumolo
    CERN, Geneva, Switzerland
  
  Multibunch instabilities due to beam-coupling impedance can be a critical limitation for synchrotrons operating with many bunches. It is particularly true for the LHC under nominal conditions, where according to theoretical predictions the 2808 bunches rely entirely on the performance of the transverse feedback system to remain stable. To study these instabilities, the HEADTAIL code has been extended to simulate the motion of many bunches under the action of wake fields. All the features already present in the single-bunch version of the code, such as synchrotron motion, chromaticity, amplitude detuning due to octupoles and the ability to load any kind of wake fields through tables, have remained available. This new code has been then parallelized in order to track thousands of bunches in a reasonable amount of time. The code was benchmarked against theory and exhibited a good agreement. We also show results for bunch trains in the LHC and compare them with beam-based measurements.  
 
MOPS076 Long Range Wakefields in the SwissFEL C-band Linac HOM, linac, simulation, impedance 781
 
  • A. Citterio, M. Aiba, R. Zennaro
    PSI, Villigen, Switzerland
  
  The SwissFEL main linac consists of more than hundred constant gradient C-band accelerating structures which boost the beam energy from 410 MeV at the injector to the final nominal energy of 5.8 GeV. With a repetition rate of 100 Hz, two bunches per pulse can be accelerated with a spacing of 28 ns to feed simultaneously two different FEL arms*. Rising of the long range wakefields, both longitudinal and transverse, could affect this multibunch operation, causing degenerative effects on the quality of the second bunch. A direct computation of the longitudinal and transverse wakes by means of time domain simulations is compared with a model based on the computation of the dispersion curves of the wake modes by frequency domain simulations. A good agreement is obtained for both the synchronous frequency and impedance of all the main modes contributing to the wakefields. Moreover, the total longitudinal wake at 28 ns is below the thighter tolerances required by the beam dynamics, so that neither Higher Order Modes (HOMs) either beam loading require compensation. The effects on the beam of the long range transverse wakefields are also negligeable.
*R. Ganter et al, SwissFEL CDR, PSI report n. 10-04; http://www.psi.ch/swissfel/CurrentSwissFELPublicationsEN/SwissFELCDR_v1903.03.11-small.pdf 		 
 
TUPC004 The Luminosity for the ILC Travelling Focus Regime with Offsets and Angle Scans* luminosity, emittance, simulation, collider 991
 
  • L.I. Malysheva, O.S. Adeyemi, V.S. Kovalenko, A. Ushakov
    University of Hamburg, Hamburg, Germany
  • K. Buesser, A.F. Hartin, G.A. Moortgat-Pick, N.J. Walker
    DESY, Hamburg, Germany
  • S. Riemann, F. Staufenbiel
    DESY Zeuthen, Zeuthen, Germany
  
  One of the crucial challenges of a future linear collider is to provide high luminosity. In the current ILC design a luminosity of 2x1034 is foreseen. In order to enhance the luminosity, use of the “travelling focus” scheme is under discussion. Within this regime the hourglass effect at the interaction point can be effectively overcome by judiciously arranging for the head and tail of the bunches to be focused at a proportionally displaced longitudinal position. The effect is further enhanced by the strong beam-beam interaction which continuously focuses the bunches during collision. In principle travelling focus could provide an additional 30% luminosity. Nevertheless the regime is highly sensitive to beam-beam transverse and angular offsets at the collision point. The study of the luminosity stability for various ILC parameters using traveling focus will be presented.  
 
TUPC015 Comparative Wakefield Analysis of a First Prototype of a DDS Structure for CLIC Main Linac simulation, impedance, dipole, damping 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.  
 
TUPC020 Alignment and Wake Field Issues in the CLIC RTML emittance, linac, lattice, cavity 1039
 
  • F. Stulle, S. Döbert, A. Latina, D. Schulte
    CERN, Geneva, Switzerland
  
  At main linac injection the particle beams need to stay within tight tolerances for the transverse emittances and the pointing stability. We study how these tolerances influence alignment requirements for the RTML components and the stability of the beams entering the RTML. An emphasize is put on the booster linac and the RF cavities of the second bunch compression stage since short and long range wake fields might strongly influence beam dynamics in these parts of the RTML.  
 
TUPC026 Status of the Crab Cavity Design for the CLIC cavity, damping, 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.  
 
TUPC091 Operational Results of the Diamond-based Halo Monitor during Commissioning of SPring-8 XFEL (SACLA) electron, undulator, laser, scattering 1218
 
  • H. Aoyagi
    JASRI/SPring-8, Hyogo-ken, Japan
  • Y. Asano, H. Kitamura, T. Tanaka
    RIKEN/SPring-8, Hyogo, Japan
  
  Funding: This work is partly supported by Japan Society for the Promotion of Science, Grant-in-Aid for Scientific Research (c) 21604017.
Measurement of electron beam halo is very important issue for X-ray free electron laser and synchrotron radiation facilities, because the beam halo may cause radiation damage of undulator magnets. Furthermore, it may cause degradation in quality of electron beam, and radio activation of beam ducts and components. In order to prevent these situations, a diamond-based halo monitor (HM) has been developed for the SPring-8 Angstrom Compact free electron LAser (SACLA). We have achieved excellent detection limit of 0.3 fC/pulse for single-shot measurement, which corresponds to the ratio of 10-6 to the beam core. The commissioning of the HM, which was installed at the upstream of 90m undulator, has been carried out, and it has been figured out that the intensity of the beam halo can be measured very nicely since secondary electrons and bremsstrahlung that are emitted in the accelerator components have not been observed. We also describe systematic profile measurements of the beam halo and operational results of the HM during the commissioning of SACLA. 		 
 
TUPC117 Embedded EPICS IOC Data Acquisition System for Beam Instability Research betatron, feedback, EPICS, storage-ring 1290
 
  • N. Zhang, Y.B. Leng
    SSRF, Shanghai, People's Republic of China
  
  Funding: This research is supported by National Natural Science Fund(No.Y155131061).
To be a part of beam diagnostics system in SSRF 3.5 GeV electron storage ring, a high performance oscilloscope is introduced to build a bunch by bunch data acquisition and processing dedicated system, which is mainly used to observe individual bunch position in transverse plane and bunch charge. By analysis of Betatron oscillation amplitude distribution and corresponding filling pattern, we hope to find phenomenon about multi-bunch Wakefield effect[1] on beam Betatron oscillation for beam instability research. The system is configured as a scope IOC, and integrated into the EPICS based control system. Application of this system and some data analysis results are also discussed in this paper. 		 
 
TUPC122 Use of a Grid Waveguide for Particle Energy Determination radiation 1302
 
  • A.V. Tyukhtin
    Saint-Petersburg State University, Saint-Petersburg, Russia
  
  Funding: The Education Agency of Russian Federation and the Russian Foundation for Basic Research (09-02-00921).
We consider prospect of use of a grid waveguide for determination of energy of charge particles in bunches. The method under consideration is based on measurement of a waveguide mode frequency. Earlier we developed two variants of this method*. One of them is based on use of a thin dielectric layer in a waveguide. Other variant is based on use of a waveguide loading with a system of wires coated with a dielectric material. In this paper we offer a new version of the method under consideration. It consists in application of a circular waveguide having a grid wall instead a solid one. The grid cells are assumed to be small. The particle bunch moves along the waveguide axis. The analytical solution of the problem is obtained by means of the averaged boundary conditions. It is shown that there is the single propagating mode. The main advantage of the method consists in an enough strong dependency of particle energy on the mode frequency in some wide frequency range. Note as well that this structure is easy for manufacture and can be embedded in the accelerator channel without big difficulty.
* A.V.Tyukhtin et al., PAC’07, p.4156; A.V. Tyukhtin, EPAC’08, p.1302; A.V. Tyukhtin, Tech. Phys. Lett. 35, p.263 (2009); A.V. Tyukhtin et al., IPAC’10, p.1071.
 		 
 
TUPO005 Design Optimization for a Non-Planar Undulator for the JETI-Laser Wakefield Accelerator in Jena undulator, electron, laser, radiation 1452
 
  • V. Afonso Rodriguez, T. Baumbach, A. Bernhard, G. Fuchert, A. Keilmann, P. Peiffer, C. Widmann
    KIT, Karlsruhe, Germany
  • M. Kaluza, M. Nicolai
    IOQ, Jena, Germany
  • R. Rossmanith
    Karlsruhe Institute of Technology (KIT), Karlsruhe, Germany
  
  In a laser wakefield accelerator (LWFA), excited by a femtosecond laser pulse electrons are accelerated to several 100 MeV within a few centimeters. The energy spread of the electron beam is relatively large and varies from shot to shot. In order to obtain monochromatic photons in an undulator despite the energy spread, the following idea was proposed. Two bending magnets and a drift space in between produces dispersion so that particles with different energies have different transverse positions. The beam enters a non-planar undulator, e.g. cylindrical pole geometry, where the K-value also varies with transverse position. If the two variations in the transverse direction (particle energy and K-value) compensate each other the generated light is more monochromatic than with a conventional planar undulator. In this paper such a modified undulator design optimized for the JETI-LWFA in Jena is presented. An experiment to test this concept is in preparation.  
 
TUPO021 Dielectric Wakefield Accelerator to Drive the Future FEL Light Source FEL, linac, electron, acceleration 1485
 
  • C.-J. Jing, A. Kanareykin
    Euclid TechLabs, LLC, Solon, Ohio, USA
  • J.G. Power, A. Zholents
    ANL, Argonne, USA
  
  X-ray free-electron lasers (FELs) are expensive instruments and a large part of the cost of the entire facility is driven by the accelerator. Using a high-energy gain dielectric wake-field accelerator (DWA) instead of the conventional accelerator may provide a significant cost saving and reduction of the facility size. In this article, we investigate using a collinear dielectric wakefield accelerator to provide a high repetition rate, high current, high energy beam to drive a future FEL x-ray light source. As an initial case study, a ~100 MV/m loaded gradient, 850 GHz quartz dielectric based 2-stage, wakefield accelerator is proposed to generate a main electron beam of 8 GeV, 50 pC/bunch, ~1.2 kA of peak current, 1MHz (10 beamlines) in just 100 meters with the fill factor and beam loading considered.  
 
TUPS041 Thermo-mechanical Study of a CLIC Bunch Train hitting a Beryllium Energy Spoiler Model radiation, collimation, simulation, linac 1629
 
  • J.-L. Fernández-Hernando, D. Angal-Kalinin
    STFC/DL/ASTeC, Daresbury, Warrington, Cheshire, United Kingdom
  • J. Resta-López
    IFIC, Valencia, Spain
  
  A thermo-mechanical study of the impact a CLIC bunch train has over a beryllium energy spoiler has been made. Beryllium has a high electrical and thermal conductivity which together with a large radiation length compared to other metals makes it an optimal candidate for a long tapered design spoiler that will not generate high wakefields, which might degrade the orbit stability and affect the collider luminosity. This paper shows the progress made from the paper presented last year in IPAC 2010. While in the aforementioned paper the study of the temperature and stress was made for the duration of the bunch train this time the study shows the evolution of the stress in the spoiler body 3 microseconds after the bunch train hit.  
 
WEXB01 Advanced Acceleration Schemes electron, laser, plasma, acceleration 1945
 
  • P.A. Naik, P.D. Gupta, B.S. Rao
    RRCAT, Indore (M.P.), India
  
  Review the progress and prospects of advanced acceleration concepts, including plasma acceleration, laser acceleration, and dielectric accelerators. Report ongoing and near-future experiments, and longer-term prospects for applications (e.g. compact X-ray sources, linear colliders, hadrontherapy).  
slides icon Slides WEXB01 [8.636 MB]  
 
WEOAB02 FACET: The New User Facility at SLAC electron, positron, plasma, linac 1953
 
  • C.I. Clarke, F.-J. Decker, R.A. Erickson, C. Hast, M.J. Hogan, R.H. Iverson, S.Z. Li, Y. Nosochkov, N. Phinney, J. Sheppard, U. Wienands, W. Wittmer, M. Woodley, G. Yocky
    SLAC, Menlo Park, California, USA
  • A. Seryi
    JAI, Oxford, United Kingdom
  
  Funding: Work supported by the U.S. Department of Energy under contract number DE-AC02-76SF00515.
FACET (Facility for Advanced Accelerator and Experimental Tests) is a new User Facility at SLAC National Accelerator Laboratory. Its high power electron and positron beams make it a unique facility, ideal for beam-driven Plasma Wakefield Acceleration studies. The first 2 km of the SLAC linac produce 23 GeV, 3.2 nC electron and positron beams with short bunch lengths of 20 um. A final focusing system can produce beam spots 10um wide. User-aided Commissioning took place in summer 2011 and FACET will formally come online in early 2012. We present the User Facility, the current features, planned upgrades and the opportunities for further experiments. 		 
slides icon Slides WEOAB02 [4.772 MB]  
 
WEPC094 Energy Loss and Longitudinal Wakefield of Relativistic Short Ion Bunches in Electron Clouds electron, simulation, ion, plasma 2229
 
  • F. Yaman, O. Boine-Frankenheim, E. Gjonaj, T. Weiland
    TEMF, TU Darmstadt, Darmstadt, Germany
  • G. Rumolo
    CERN, Geneva, Switzerland
  
  Funding: Work supported by BMBF under contract 06DA9022I
The aim of our study is the numerical computation of the wakefield, impedance and energy loss for an energetic, short (< 10 ns) ion bunch penetrating an electron cloud plasma residing in the beam pipe. We use a 3-D self-consistent and higher order PIC code based on the full-wave solution of the Maxwell equations in the time domain. In our simulations we observe the induced density oscillations in the electron cloud in the longitudinal as well as in the transverse directions. A special numerical procedure is applied to compute the longitudinal wake potential and the broadband coupling impedance due to the beam-electron cloud interaction. The code is applied to the case of the CERN SPS and the projected SIS-100 at GSI. The effects of the beam pipe, electron density, bunch intensity and external magnetic dipole fields are studied. The results are compared to analytical and numerical models of reduced complexity. 		 
 
WEPC097 A Concatenation Scheme for the Computation of Beam Excited Higher Order Mode Port Signals cavity, HOM, coupling, higher-order-mode 2238
 
  • T. Flisgen, H.-W. Glock, U. van Rienen
    Rostock University, Faculty of Computer Science and Electrical Engineering, Rostock, Germany
  
  Ongoing studies investigate in how far higher order mode (HOM) port signals of superconducting RF cavities can be used for machine and beam diagnostics. Apart from experiments e.g. at the FLASH facility at DESY in Hamburg, numerical modelling is needed for the prediction of HOM coupler signals. For this purpose, the RF properties of the entire accelerating module have to be taken into account, since higher order modes can propagate along the cavity chain. A discretization of the full chain, followed by a wake field simulation is only feasible with powerful and expensive cluster computers. Instead, an element wise wake field simulation of sub-sections of the chain, followed by a suitable concatenation scheme can be performed on standard hardware assuming the beam to be sufficiently stiff. In this paper a concatenation scheme for the computation of beam excited HOM port signals is derived as a generalization of the Coupled S-Parameter scheme CSC. Furthermore, the validity of the method is shown for a sample structure.  
 
WEPZ008 Experimental Plans to Explore Dielectric Wakefield Acceleration in the THz Regime acceleration, simulation, electron, dipole 2781
 
  • F. Lemery, D. Mihalcea, P. Piot
    Northern Illinois University, DeKalb, Illinois, USA
  • C. Behrens, E. Elsen, K. Flöttmann, C. Gerth, G. Kube, B. Schmidt
    DESY, Hamburg, Germany
  • J. Osterhoff
    LBNL, Berkeley, California, USA
  • P. Stoltz
    Tech-X, Boulder, Colorado, USA
  
  Funding: This work was supported by the Defense Threat Reduction Agency, Basic Research Award \# HDTRA1-10-1-0051, to Northern Illinois University
Dielectric wakefield accelerators have shown great promise toward high-gradient acceleration. We investigate tow experiments in preparation to explore the performance of cylindrically-symmetric and slab-shaped dielectric-loaded waveguides. The planned experiments at Fermilab and DESY will use unique pulse shaping capabilities offered at these facilities. The superconducting test accelerator at FNAL will ultimately provide flat beams with variable current profiles needed for enhancing the transformer ratio. The FLASH facility at DESY recently demonstrated the generation of a ramped round beam current profile that will enable us to explore the performance of cylindrically-symmetric structures. Finally both of these facilities incorporate superconducting linear accelerator that could generate bunch trains with closely spaced bunches thereby opening the exploration of dynamical effects in dielectric wakefield accelerators. We present the planned layout and simulated experimental performances. 		 
 
WEPZ012 Influence of Transition Radiation on Formation of a Bunch Wakefield in a Circular Waveguide vacuum, radiation, plasma, acceleration 2793
 
  • T.Yu. Alekhina, A.V. Tyukhtin
    Saint-Petersburg State University, Saint-Petersburg, Russia
  
  Funding: The Education Agency of Russian Federation.
Investigation of a field of a particle bunch in a waveguide loaded with a dielectric is important for the wakefield acceleration (WFA) technique and other problems in the accelerator physics. One of subjects of investigation in this area consists in analysis of transition radiation generated by the bunch flying into (out of) the dielectric structure. This radiation can be both destructive (for WFA) and useful (for diagnostics of bunch or material). We investigate the total field of small bunch crossing a boundary between two dielectrics in the waveguide. It includes a “forced” field and a “free” one. The “forced” field is the field of the charge in the unbounded waveguide (it can contain the wakefield). The “free” field is connected with influence of the boundary (it includes transition radiation). Two cases are analyzed in detail: the bunch flies from vacuum into dielectric and from dielectric into vacuum. The behavior of the field depending on distance and time is explored analytically and numerically. Some interesting physical effects are noted. As well, we make a comparison with the case of intersection between vacuum and cold plasma. 		 
 
WEPZ014 Upgrade of the Argonne Wakefield Accelerator Facility (AWA): Commissioning of the RF Gun and Linac Structures for Drive Beam Generation gun, electron, linac, acceleration 2799
 
  • M.E. Conde, D.S. Doran, W. Gai, R. Konecny, W. Liu, J.G. Power, Z.M. Yusof
    ANL, Argonne, USA
  • S.P. Antipov, C.-J. Jing
    Euclid TechLabs, LLC, Solon, Ohio, USA
  • E.E. Wisniewski
    Illinois Institute of Technology, Chicago, Illinois, USA
  
  Funding: Work supported by the U.S. Department of Energy under contract No. DE-AC02-06CH11357.
Research at the AWA Facility has been focused on the development of electron beam driven wakefield structures. Accelerating gradients of up to 100 MV/m have been excited in dielectric loaded cylindrical structures operating in the microwave range of frequencies. Several upgrades, presently underway, will enable the facility to explore higher accelerating gradients, and also be able to generate longer RF pulses of higher intensity. The major items included in the upgrade are: (a) a new RF gun with a higher quantum efficiency photocathode will replace the RF gun that has been used to generate the drive bunches; (b) the existing RF gun will be used to generate a witness beam to probe the wakefields; (c) three new L-band RF power stations, each providing 25 MW, will be added to the facility; (d) five linac structures will be added to the drive beamline, bringing the beam energy up from 15 MeV to 75 MeV. The upgraded drive beam will consist of bunch trains of up to 32 bunches spaced by 0.77 ns with up to 100 nC per bunch. The goal of future experiments is to reach accelerating gradients of several hundred MV/m and to extract RF pulses with GW power level. 		 
 
WEPZ015 Staging in Two Beam Dielectric Wakefield Accelerators cavity, acceleration, kicker, septum 2802
 
  • J.G. Power, M.E. Conde, W. Gai, C.-J. Jing
    ANL, Argonne, USA
  
  Funding: The work is supported by the U.S. Department of Energy under Contract No. DE-AC02-06CH11357 with Argonne National Laboratory.
A new experimental program to demonstrate staging in a two beam dielectric wakefield accelerator (DWA) is being planned at the Argonne Wakefield Accelerator facility. DWA uses a drive beam to generate acceleration fields to accelerate a main beam and is one of the most promising advanced acceleration methods being pursued for a future high-energy physics linear collider. Staging is the ability to use two accelerating modules back to back to accelerate a charged particle bunch and it is one of basic requirements of any acceleration method. In this paper, a new beamline design consisting of a fast kicker to pick pulses from the drive bunch train and deliver them to the individual acceleration modules will be presented. 		 
 
WEPZ016 Generation and Characterization of Electron Bunches with Ramped Current Profiles at the FLASH Facility electron, laser, linac, free-electron-laser 2805
 
  • P. Piot
    Fermilab, Batavia, USA
  • C. Behrens, C. Gerth, M. Vogt
    DESY, Hamburg, Germany
  • F. Lemery, D. Mihalcea
    Northern Illinois University, DeKalb, Illinois, USA
  
  Funding: This work was supported the Defense Threat Reduction Agency, Basic Research Award # HDTRA1-10-1-0051, to Northern Illinois University and the German's Bundesministerium f\"ur Bildung und Forschung
We report on the successful generation of electron bunches with current profiles that have a quasi-linear dependency on the longitudinal coordinate. The technique relies on impressing nonlinear correlations in the longitudinal phase space using a linac operating at two frequencies (1.3 and 3.9 GHz) and a bunch compressor. Data taken for various accelerator settings demonstrate the versatility of the method. The produced bunches have parameters well matched to drive high-gradient accelerating field with enhanced transformer ratio in beam-driven accelerators based on sub-mm-sizes dielectric or plasma structures. 		 
 
WEPZ021 Self-Consistent Dynamics of Electromagnetic Pulses and Wakefields in Laser-Plasma Interactions laser, plasma, simulation, space-charge 2811
 
  • A. Bonatto, R. Pakter, F.B. Rizzato
    IF-UFRGS, Porto Alegre, Brazil
  
  In the present work we study the stability of laser pulses propagating in a cold relativistic plasma, which can be of interest for particle acceleration schemes. After obtaining a Lagrangian density from the one-dimensional equations for the laser pulse envelope and the plasma electron density, we define a trial function and apply the variational approach in order to obtain an analytical model which allows us to calculate an effective potential for the pulse width. Using this procedure, we analyze the stability of narrow and large laser pulses and then compare its results with numerical solutions for the envelope and density equations.  
 
WEPZ023 Results from Plasma Wakefield Acceleration Experiments at FACET plasma, acceleration, electron, diagnostics 2814
 
  • S.Z. Li, C.I. Clarke, R.J. England, J.T. Frederico, S.J. Gessner, M.J. Hogan, R.K. Jobe, M.D. Litos, D.R. Walz
    SLAC, Menlo Park, California, USA
  • E. Adli
    University of Oslo, Oslo, Norway
  • W. An, C.E. Clayton, C. Joshi, W. Lu, K.A. Marsh, W.B. Mori, S. Tochitsky
    UCLA, Los Angeles, California, USA
  • P. Muggli
    USC, Los Angeles, California, USA
  
  Funding: Work supported by the U.S. Department of Energy under contract number DE- AC02-76SF00515.
We report initial results of the Plasma Wakefield Acceleration (PWFA) Experiments performed at FACET - Facility for Advanced aCcelertor Experimental Tests at SLAC National Accelerator Laboratory. At FACET a 23 GeV electron beam with 1.8x1010 electrons is compressed to 20 microns longitudinally and focused down to 10 microns x 10 microns transverse spot size for user driven experiments. Construction of the FACET facility completed in May 2011 with a first run of user assisted commissioning throughout the summer. The first PWFA experiments will use single electron bunches combined with a high density lithium plasma to produce accelerating gradients >10GeV/m benchmarking the FACET beam and the newly installed experimental hardware. Future plans for further study of plasma wakefield acceleration will be reviewed. 		 
 
WEPZ024 Some Considerations in Realizing a TeV Linear Collider Based on the PDPWA Scheme proton, electron, plasma, collider 2817
 
  • G.X. Xia, A. Caldwell
    MPI-P, München, Germany
  • P. Muggli
    MPI, Muenchen, Germany
  
  Proton-driven plasma wakefield acceleration (PDPWA) has recently been proposed as an approach to bring the electron beam to the energy frontier in a single passage of acceleration. Particle-in-Cell (PIC) simulation shows that a TeV proton bunch, with a bunch intensity of 1011, and a bunch length as short as 100 microns can resonantly excite a large amplitude plasma wakefield and accelerate an externally injected electron bunch to 600 GeV in a single stage of 500 m long plasma. This novel PDPWA scheme may open a new path for designing a TeV linear lepton collider by using the currently available proton drivers. In this paper, we investigate some key issues, e.g. bunch length, centre-of-mass (CoM) energy, luminosity and dephasing in realizing a TeV linear collider based on the PDPWA scheme.  
 
WEPZ027 Stabilization of the LWFA and its Application to the Single-shot K-edge Densitometry electron, scattering, laser, emittance 2823
 
  • K. Koyama, H. Madokoro, Y. Matsumura
    University of Tokyo, Tokyo, Japan
  • R. Kuroda, K. Yamada
    AIST, Tsukuba, Ibaraki, Japan
  • H. Masuda, M. Uesaka
    The University of Tokyo, Nuclear Professional School, Ibaraki-ken, Japan
  • S. Masuda
    Osaka University, Suita, Osaka, Japan
  
  Funding: This work was supported in part by Global COE Program “Nuclear Education and Research Initiative,” MEXT, Japan
Injection of electrons into a laser wakefield accelerator (LWFA) via a wavebreaking process was investigated in order to obtain stable output of electron bunches. A density down ramp for occurring the wavebreaking was formed by an oblique shockwave, which was excited by setting a little flow-deflector on an edge of the supersonic nozzle of high-Mach number (M=5). Parameters of the jet were examined by using PIC code and evaluated by using an interferometer, the density was 1019cm-3, density ratio was 2, and the characteristic length was 70 microns. Injection experiments using 7-TW laser pulses suggested that electrons were injected in the density ramp. Since the all-optical Compton X-ray is attractive source for an accurate densitometry, a preliminary experiment of a single-shot K-edge densitometry was performed by using X-ray pulses generated by the laser-Compton scattering (LCS) device based on a compact S-band 40 MeV linac at AIST. The single-shot K-edge densitometry was also applicable to evaluate the transverse emittance of electron bunches. 		 
 
WEPZ034 Double Resosnant Plasma Wakefields plasma, laser, simulation, electron 2838
 
  • B.D. O'Shea, A. Fukasawa, B. Hidding, J.B. Rosenzweig, S. Tochitsky
    UCLA, Los Angeles, California, USA
  • D.L. Bruhwiler
    Tech-X, Boulder, Colorado, USA
  
  Present work in Laser Plasma Accelerators focuses on a single laser pulse driving a non-linear wake in a plasma. Such single pulse regimes require ever increasing laser power in order to excite ever increasing wake amplitudes. Such high intensity pulses can be limited by instabilities as well engineering restrictions and experimental constraints on optics. Alternatively we present a look at resonantly driving plasmas using a laser pulse train. In particular we compare analytic, numerical and VORPAL simulation results to characterize a proposed experiment to measure the wake resonantly driven by four Gaussian laser pulses. The current progress depicts the interaction of 4 CO2 laser pulses, λlaser = 10.6μm, of 3 ps full width at half max- imum (FWHM) length separated peak-to-peak by 18 ps, each of normalized vector potential a0 ≃ 0.7. Results con- firm previous discourse (*,**) and show, for a given laser pro- file, an accelerating field on the order of 900 MV/m, for a plasma satisfying the resonant condition, ωp=π/tfwhm.
* Umstadter, D., et al, Phys. Rev. Lett. 72, 1224
** Umstadter, D., et al, Phys. Rev. E 51, 3484
 		 
 
THPC125 Study of some Design Concepts and Collective Effects in the MAX IV Linac linac, emittance, simulation, sextupole 3176
 
  • F. Curbis, M. Eriksson, O.E. Karlberg, S. Thorin, S. Werin
    MAX-lab, Lund, Sweden
  • D. Angal-Kalinin, P.H. Williams
    STFC/DL/ASTeC, Daresbury, Warrington, Cheshire, United Kingdom
  
  The MAX IV linac will be used both for injection and top up into two storage rings, and as a high brightness injector for a Short Pulse Facility (SPF) and an FEL (phase 2). Compression is done in two double achromats with positive R56. The natural second order momentum compaction, T566, from the achromats is used together with weak sextupoles to linearise longitudinal phase space, leaving no need for a harmonic cavity for linearization of longitudinal phase space. In this proceeding we present the design of the achromat compressors and results from particle tracking through the MAX IV linac in high brightness mode. We also investigate emittance dilution due to CSR, in the achromat compressors, and transverse wakefields in a high beta function lattice.  
 
THPZ021 Effect of Coherent Synchrotron Radiation at the SuperKEKB Damping Ring vacuum, emittance, damping, linac 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.