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space-charge

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MOZAG01 Simulations of the Emittance Compensation in Photoinjectors and Comparison with SPARC Measurements emittance, simulation, gun, linac 21
 
  • C. Ronsivalle, L. Giannessi, M. Quattromini
    ENEA C. R. Frascati, Frascati (Roma)
  • A. Bacci, A. R. Rossi, L. Serafini
    INFN-Milano, Milano
  • E. Chiadroni, M. Ferrario, L. Ficcadenti, D. Filippetto, V. Fusco, B. Marchetti, M. Migliorati, A. Mostacci, L. Palumbo, C. Vaccarezza
    INFN/LNF, Frascati (Roma)
  • A. Cianchi
    INFN-Roma II, Roma
  FEL photoinjectors are based on the emittance compensation process, by which a high brightness beam can be accelerated without degradation. The experimental results obtained in the SPARC facility for which the beam dynamics has been extensively simulated confirm the theoretical predictions. The paper illustrates the most relevant beam dynamics results as well as a comparison between simulations and measurements.  
slides icon Slides  
 
MOPC023 ARC-EN-CIEL Beam Dynamics emittance, laser, brightness, gun 115
 
  • A. Loulergue, M.-E. Couprie
    SOLEIL, Gif-sur-Yvette
  • C. Bruni
    LAL, Orsay
  ARC-EN-CIEL project is based on a CW 1.3 GHz superconducting linac accelerator delivering high charge, subpicosecond and low emittance electron bunches at high repetition rate. According to the electron energy, it provides tunable light source of high brightness in the VUV to soft X-ray wavelength domain. The project will evolve into three phases: first and second phases are based on high brightness single pass SC linac configuration with a low average current (few μA), while third phase comports recirculation loops to increase the average current (up to 100 mA). This paper deals with electron beam dynamics issues for the single pass configuration in the two first phases from the RF gun to undulators including magnetic compression stages. In the ERL configuration of the third phase, the accelerator scheme and focusing are investigated in order to take into account collective effects as Beam Break Up instability.  
 
MOPC024 Calculation of Coherent Synchrotron Radiation in General Particle Tracer shielding, electron, emittance, synchrotron 118
 
  • I. V. Bazarov
    Cornell University, Department of Physics, Ithaca, New York
  • T. Miyajima
    KEK, Ibaraki
  General Particle Tracer (GPT) is a particle tracking code, which includes 3D space charge effect based on nonequidistant multigrid Poisson solver or point-to-point method. It is used to investigate beam dynamics in ERL and FEL injectors. We have developed a new routine to simulate coherent synchrotron radiation (CSR) in GPT based on the formalism of Sagan*. The routine can calculate 1D-wake functions for arbitrary beam trajectories as well as CSR shielding effect. In particular, the CSR routine does not assume ultrarelativistic electron beam and is therefore applicable at low beam energies in the injector. Energy loss and energy spread caused by CSR effect were checked for a simple circular orbit, and compared with analytic formulas. In addition, we enhanced the 3D space charge routine in GPT to obtain more accurate results in bending magnets.

*D. Sagan, EPAC06, pp. 2829-2831.

 
 
MOPC029 Longitudinal Structure of Electron Bunches at the Micrometer Scale from Spectroscopy of Coherent Transition Radiation radiation, electron, linac, collective-effects 130
 
  • B. Schmidt, C. Behrens, S. Wesch
    DESY, Hamburg
  • H. Delsim-Hashemi, J. Rossbach, P. Schmüser
    Uni HH, Hamburg
  At the free electron laser FLASH in Hamburg, a longitudinal bunch compression scheme is used resulting in a longitudinal current profile with a narrow leading spike. Part of this spike is responsible for producing high-intensity short FEL pulses via the SASE process. The width and the structure of the current spike, which are key parameters for the efficiency of the SASE process, are barely accessible to direct measurements in the time domain. Using an infrared multi-stage grating spectrometer, we have studied the spectral composition of coherent transition radiation from single electron bunches. The data show that the 'fundamental width' of the current spike is about 40 fs (fwhm) with prominent substructures down to the 10 fs scale. The intensity fluctuations of coherent radiation in the corresponding wavelength range are strongly correlated to the fluctuations of the FEL pulse energy. Extension of the method to the near infrared regime have revealed micro-structures with characteristic lengths from a few micrometers down to fractions of a micrometer. Their interrelation with the parameters of the electron beam and the compression system have been studied.  
 
MOPC034 Collective Effects in a Short-Pulse FEL Driver emittance, linac, electron, laser 145
 
  • P. H. Williams, H. L. Owen
    STFC/DL/ASTeC, Daresbury, Warrington, Cheshire
  • G. Bassi
    Cockcroft Institute, Warrington, Cheshire
  • S. Thorin
    MAX-lab, Lund
  There is much interest in the provision of coherent, tunable VUV and soft X-ray pulses of duration less than 10fs. A 1.3 GHz linac driver concept has been developed, and in this paper we address collective effects in the short electron bunches using start-to-end modelling. In particular, we examine the limitations from coherent radiation and induced microbunching, and their impact on the design of the accelerator system.  
 
MOPC130 Space Charge Loss Mechanisms Associated with Half Integer Resonance on the ISIS Synchrotron simulation, resonance, emittance, synchrotron 373
 
  • C. M. Warsop, D. J. Adams, B. G. Pine
    STFC/RAL/ISIS, Chilton, Didcot, Oxon
  ISIS is the spallation neutron source at the Rutherford Appleton Laboratory in the UK. Operation centres on a 50 Hz proton synchrotron, which accelerates ~3·1013 ppp from 70 to 800 MeV, corresponding to mean beam powers of 0.2 MW. Beam loss limits operational intensity, and a main contributing mechanism is the action of half integer resonance under high space charge. Progress on studies using particle in cell simulations to explore the evolution of envelope motion, associated 2:1 parametric halo, growth of particles from the outer core, and effects of dispersion and longitudinal motion is presented. Comparisons are made with relevant theoretical models and progress on experimental studies summarised, presently emphasising the simplified 2D coasting beam case.  
 
MOPD012 Half Wave Injector Design for WiFEL emittance, gun, cathode, linac 469
 
  • R. A. Legg
    UW-Madison/SRC, Madison, Wisconsin
  • W. Graves
    MIT, Cambridge, Massachusetts
  • T. L. Grimm
    Niowave, Inc., Lansing, Michigan
  • P. Piot
    Fermilab, Batavia, Illinois
  Seeded FELs will require exceptional beam quality. The Wisconsin FEL (WiFEL) requires peak currents of greater than 1 kA with less than 1 mm-mrad transverse slice emittance and 1·10-4 δp/p at the undulator. To perform the obligatory bunch compression after the injector without allowing micro-bunching will require very smooth bunch energy and density profiles and relatively low compression ratios. An injector which uses a low frequency, superconducting, half wave resonator gun combined with self-inflating, ellipsoidal bunches* to meet those requirements is described. The superconducting radio frequency TEM-class cavities have been in use for more than 25 years and because of their potential for flat field profiles, are desirable as electron gun structures. A Superfish model and field map of the specific gun cavity is presented. ASTRA** simulations from the cathode to 120MeV are provided. A description is given of the technique used to emittance compensate the space charge induced energy chirp while maintaining the peak bunch current.

* O. J.Luiten, et al., Phys. Rev. Lett. Vol 93, 094802 (2004)
** K. Floetmann, ASTRA, www.desy.de/~mpyflo

 
 
MOPD023 Parametric Study of a Novel Coaxial Bunched Beam Space-charge Limit electron, plasma, focusing, klystron 493
 
  • M. Hess
    IUCF, Bloomington, Indiana
  Recently, a non-trivial space-charge limit for off-axis bunched electron beams in a coaxial conducting structure was derived theoretically*. The space-charge limit describes the minimum strength of an external solenoidal focusing field which is needed to stabilize the beam’s center-of-mass motion in the presence of induced surface charges on the coaxial structure. In this paper, we perform a parametric study of the space-charge limit to numerically determine its dependency on the conducting structure geometry, i.e., the ratio of the inner and outer conductor radii, as well as its’ dependency on the transverse and longitudinal bunch distributions. As an application, we show how this parametric study can be important for the design of high-power microwave sources, such as the UC-Davis/SLAC 2.8 GHz coaxial ubitron oscillator**.

*M. Hess, accepted for publication in IEEE Trans. Plasma Sci. (2008).
**A. J. Balkcum et al. IEEE Trans. Plasma Sci., vol. 26, pp. 548-555, 1998.

 
 
MOPP049 Collective Effects in the CLIC Damping Rings impedance, ion, damping, emittance 658
 
  • G. Rumolo, J. B. Jeanneret, Y. Papaphilippou, D. Quatraro
    CERN, Geneva
  The possible performance limitations coming from collective effects in the CLIC damping rings are the subject of this paper. In particular, the consequences of space charge, due to the very high beam brilliance, and of the resistive wall impedance, due to the locally very small beam pipe, are considered potentially dangerous in spite of the high beam energy. Hence, they have been studied in detail with the HEADTAIL code, which has been modified in order to take into account a finer lattice structure as well as multi-bunch effects of the resistive wall wake field. The study aims at setting the intensity thresholds determined by these phenomena.  
 
MOPP075 Experimental Generation and Characterization of Uniformly Filled Ellipsoidal Electron Beam Distributions laser, electron, cathode, emittance 724
 
  • P. Musumeci, J. Moody, J. B. Rosenzweig, C. M. Scoby
    UCLA, Los Angeles, California
  For forty years, uniformly filled ellipsoidal beam distributions have been studied theoretically, as they have had the promise of generating self-fields that produce forces linear in the coordinate offset in all three directions. More recently, a scheme for producing such distributions, which depends on the strong longitudinal expansion of an initially very short beam under its own space charge forces, has been proposed. Here we present the experimental demonstration of this scheme, obtained by illuminating the cathode in an rf photogun with an ultra-short laser pulse (~35 fs rms) with an appropriate transverse profile. The resulting 4 MeV beam spatiotemporal (x,t) distribution is imaged using an rf deflecting cavity with 50 fsec resolution. A temporal asymmetry in the ellipsoidal profile, due to image charge effects at the photocathode, is observed at higher charge operation. This distortion is also found to degrade the transverse beam quality.  
 
TUPC002 Design of a Tomography Module for the PITZ Facility quadrupole, diagnostics, emittance, electron 1038
 
  • G. Asova, K. Floettmann
    DESY, Hamburg
  • D. J. Holder, B. D. Muratori
    STFC/DL/ASTeC, Daresbury, Warrington, Cheshire
  • S. Khodyachykh, S. A. Korepanov, M. Krasilnikov, S. Rimjaem, F. Stephan
    DESY Zeuthen, Zeuthen
  The goal of the Photo Injector Test Facility at DESY in Zeuthen (PITZ) is to develop sources of high phase-space density electron beams that are required for the successful operation of SASE FELs. This requires detailed characterization of the sources and therefore the development of suitable advanced diagnostics. As part of the ongoing upgrade towards higher beam energies, new diagnostics components are being installed. An example is a tomography module for transverse phase space reconstruction which is designed to operate in the energy range between 15 and 40 MeV. The module consists of four observation screens with three FODO cells between them. A number of upstream quadrupoles are used to match the beam envelope parameters to the optics of the FODO lattice. This contribution presents the final design of the tomography module. Data from numerical simulations are used to illustrate the expected performance and to compare it to a simplified setup of two quadrupoles. The quality of the reconstruction is revised with the help of different algorithms.  
 
TUPC027 Spatial Autocorrelation for Transverse Beam Quality Characterization laser, emittance, focusing, brightness 1107
 
  • V. Fusco, M. Ferrario
    INFN/LNF, Frascati (Roma)
  • C. Ronsivalle
    ENEA C. R. Frascati, Frascati (Roma)
  Low emittance beams are required for high brightness beams applications. Contributions to emittance degradations come from electromagnetic fields’ non-linearities which can be reduced using a transversally and longitudinally uniform beam. For these reasons the evaluation of the beam quality is a very important task. Concerning the transverse analysis the spatial correlation parameter has been introduced: it gives an evaluation of how beam non-uniformity is distributed. The paper describes the spatial autocorrelation concept and applies it to the evaluation of a laser beam for high brightness beam applications. Moreover the paper shows the spatial autocorrelation evolution along a photo-injector as an additional tool for beam dynamics studies.  
 
TUPC078 The Gun Spectrometer Design for the FERMI@Elettra Project gun, quadrupole, simulation, diagnostics 1233
 
  • G. Penco, D. Castronovo, M. Trovo, D. Zangrando
    ELETTRA, Basovizza, Trieste
  In the FERMI linac layout the first spectrometer has been located close to the exit of the photoinjector gun at about 5 MeV. The main purpose of this equipment is measuring the energy and energy spread of the beam. Combining the spectrometer with Yag screens and Cerenkov radiators allows the investigation and characterization of eventual deterioration of the longitudinal profile due to the space charge forces and microbunching instabilities. The design specification of the magnet and multi-particle tracking code simulation results are presented in this paper.  
 
TUPC109 Analysis of Measurement Errors in Residual Gas Ionisation Profile Monitors in a High Intensity Proton Beam ion, simulation, proton, synchrotron 1317
 
  • R. E. Williamson, S. J. Payne, B. G. Pine, C. M. Warsop
    STFC/RAL/ISIS, Chilton, Didcot, Oxon
  ISIS is the pulsed neutron and muon source based at the Rutherford Appleton Laboratory in the UK. Operation is centred on a loss-limited 50 Hz proton synchrotron which accelerates ~3·1013 protons per pulse from 70 MeV to 800 MeV, corresponding to a mean beam power of 0.2 MW. Beam profile measurements are a key component of both ISIS operational running and R&D beam studies. Understanding and quantifying limitations in these monitors is essential, and has become more important as work to optimise and study the beam in more detail has progressed. This paper presents 3D field and ion trajectory modelling of the ISIS residual gas ionization profile monitors, including the effects of non-uniformity in longitudinal and transverse drift fields, and beam space charge. The simulation model allows comparison between the input beam profile, and that deduced from ion currents. The resulting behaviour, corrections and errors are then compared with experimental data from the ISIS synchrotron.  
 
TUPP038 On the Longitudinal Coupling Impedance and Transmission Coefficient from Uniform and Hollow Ring Sources impedance, coupling, synchrotron, electromagnetic-fields 1625
 
  • A. M. Al-Khateeb, O. Boine-Frankenheim, R. W. Hasse
    GSI, Darmstadt
  • J. M. Shobaki
    Yarmouk, Irbid
  The longitudinal coupling impedance and the transmission coefficient resulting from a thin ring and from a uniform disk are obtained analytically for a resistive cylindrical beam-pipe of finite wall thickness. The impedances are derived and then compared with the well known corresponding expression for perturbations on a uniform, coasting beam. The transmission coefficients from both sources are found to be exactly the same. Differences do appear in the expressions for the electromagnetic fields within the beam region, and therefore leading to different coupling impedances. By applying the results to parameters relevant for the SIS-18 synchrotron at GSI, it is found that the formula from the ring source underestimates the space-charge impedance at all beam energies and it shows a noticeable deviation from the disk formula for all frequencies. Although their mathematical expressions are different, resistive-wall impedances from the two sources are found to be numerically equal. The space-charge impedances become equal asymptotically only in the so called ultra-relativistic limit.

A. Al-Khateeb is on leave from Yarmouk University, Irbid, Jordan

 
 
TUPP048 Collective Effects in the EMMA Non-scaling FFAG acceleration, emittance, simulation, beam-loading 1652
 
  • S. Machida, D. J. Kelliher
    STFC/RAL/ASTeC, Chilton, Didcot, Oxon
  • J. S. Berg
    BNL, Upton, Long Island, New York
  • S. R. Koscielniak
    TRIUMF, Vancouver
  EMMA is an electron machine to study beam dynamics in a linear nonscaling FFAG. We wish to verify that the behavior predicted by the theory and simulation is correct. In particular, we will study, with large emittance beams, a novel accelerating mode outside an rf bucket, and the effects of crossing "resonances." In EMMA, some collective effects become a concern even though the beam stays in the ring for only 10 to 20 turns. We report studies of direct and image space charge, beam loading, and other collective effects with a tracking simulation. Space charge effects, already potentially significant in EMMA, are enhanced by the fact that the beam passes through the beam pipe off-center. There is some possibility of a negative mass instability for some operation modes. We will show several 3D simulation results for space charge and beam loading effects and pure longitudinal simulation for the negative mass instability.  
 
TUPP082 Longitudinal Stability of Flat Bunches with Space-charge or Inductive Impedance impedance, damping, synchrotron, dipole 1721
 
  • F. Zimmermann
    CERN, Geneva
  • I. Santiago Gonzalez
    University of the Basque Country, Bilbao
  We study the loss of Landau damping for the longitudinal plane via the ''Sacherer formalism''. Stability limits are calculated for several longitudinal beam distributions, in particular for two types of flat bunches, which could be of interest to the LHC upgrade. The resulting Landau stability diagrams are computed and displayed for different azimuthal modes. A general recipe is given for calculating the threshold intensity in the case of a capacitive impedance below transition or, equivalently, for a purely inductive impedance above transition. Specific results are finally presented for the case of the PS Booster, as an example of space-charge impedance below transition, and for the SPS, as an example of inductive impedance above transition.  
 
TUPP084 Parallel Computation of Integrated Electromagnetic, Thermal and Structural Effects for Accelerator Cavities simulation, gun, vacuum, emittance 1724
 
  • V. Akcelik, A. E. Candel, A. C. Kabel, K. Ko, L. Lee, Z. Li, C.-K. Ng, L. Xiao
    SLAC, Menlo Park, California
  The successful operation of accelerator cavities has to satisfy both rf and mechanical requirements. It is highly desirable that electromagnetic, thermal and structural effects such as cavity wall heating and Lorentz force detuning in superconducting rf cavities can be addressed in an integrated analysis. Based on the SLAC parallel finite-element code infrastructure for electromagnetic modeling, a novel multi-physics analysis tool has been developed to include additional thermal and mechanical effects. The speedup from parallel computation enables virtual prototyping of accelerator cavities on computers, which would substantially reduce the cost and time of a design cycle. The multi-physics tool will be applied to the LCLS rf gun and a superconducting rf gun cavity.  
 
TUPP086 Efficient 3D Space Charge Calculations by Self-adaptive Multigrid Methods Using the Chombo Framework brightness, electron, vacuum, simulation 1730
 
  • C. R. Bahls, G. Pöplau, U. van Rienen
    Rostock University, Faculty of Computer Science and Electrical Engineering, Rostock
  Current and future accelerator design requires efficient 3D space charge computations for high brightness bunches which should be as precise and fast as possible. One possible approach for space charge calculations is the particle-mesh-method, where the potential is calculated in the rest frame of the bunch by means of Poisson's equation. For an efficient solution of this elliptic PDE an appropriate adaptive discretization of the domain is required. Especially it has to take into account discontinuities in the distribution of the particles. The solution method we investigate in this paper is a self-adaptive multigrid method applying composite grids. To accomplish this, we use the library Chombo* which is being developed as a framework for adaptive multiresolution solvers for elliptic and hyperbolic partial differential equations.

*Developed and distributed by the Applied Numerical Algorithms Group
of Lawrence Berkeley National Lab., http://seesar.lbl.gov/ANAG/chombo/

 
 
TUPP088 Software Components for Electron Cloud Simulation electron, simulation, proton, background 1735
 
  • D. R. Dechow, P. Stoltz
    Tech-X, Boulder, Colorado
  • J. F. Amundson, P. Spentzouris
    Fermilab, Batavia, Illinois
  • B. Norris
    ANL, Argonne, Illinois
  The Synergia2 beam dynamics code is an attempt to incorporate state-of-the-art space charge models from the Impact code into the Chef accelerator tracking code. The need to add new accelerator physics capabilities to the Synergia2 framework has led to software development efforts based on the Common Component Architecture (CCA). The CCA is a specification and a toolset for developing HPC from interchangeable parts, called components. Electron cloud is a potentially limiting effect in the performance of both high-intensity electron and proton machines. The modeling of electron cloud effects is important for the Fermilab main injector. Here, electron cloud effects are expected to play a significant role when the main injector operates in the regime of a high-intensity proton source for the neutrino program. In the ideal case, computational accelerator physicists would like to be able model electron cloud generation and dynamics in a single, self-consistent simulation. As a first step towards creating component-based, electron cloud generation simulations, this work describes a CCA component created from TxPhysics, a library of impact and field ionization routines.  
 
TUPP098 The 3D Space Charge Field Solver MOEVE and the 2D Bassetti-Erskine Formula in the Context of Beam - E-cloud Interaction Simulations positron, simulation, damping, electron 1759
 
  • A. Markovik, G. Pöplau, U. van Rienen
    Rostock University, Faculty of Computer Science and Electrical Engineering, Rostock
  In this paper the fields computed with our 3D space charge field solver MOEVE are compared to those obtained by means of the Bassetti-Erskine formula, which is a widely used 2D approximation of the electric field of a Gaussian bunch. In particular we are interested in the transversal fields of very flat bunches as the ILC or the KEKB positron bunch. Supposing a longitudinal Gaussian distribution of the bunches, we compare the computed transversal fields for a certain line density of the positron bunch. It turns out that the fields from the 2D and the 3D computation coincide very good.  
 
TUPP103 The Performance of 3D Space Charge Models for High Brightness Electron Bunches simulation, brightness, electron, cathode 1770
 
  • G. Pöplau, U. van Rienen
    Rostock University, Faculty of Computer Science and Electrical Engineering, Rostock
  • K. Floettmann
    DESY, Hamburg
  Precise and fast 3D space charge calculations for high brightness, low emittance electron beams are of growing importance for the design of future accelerators and light sources. The program package Astra (A space charge tracking algorithm) has been successfully used in the design of linac and rf photo injector systems. The Astra suite originally developed by K. Flöttmann tracks macro particles through user defined external fields including the space charge field of the particle cloud. In this paper we investigate the performance of the 3D space charge models implemented in Astra. These are the FFT-Poisson solver with the integrated Green's function and the iterative Poisson solver based on the multigrid technique. The numerical tests consider the accuracy of the solvers for model bunches as well as the performance within a typical simulation for the XFEL.  
 
WEPC085 Matching with Space Charge quadrupole, diagnostics, focusing, emittance 2192
 
  • B. D. Muratori, D. J. Holder
    STFC/DL/ASTeC, Daresbury, Warrington, Cheshire
  This paper explores the possibility of performing matching in the presence of space charge to an acceptable and useful level. Space charge gives rise to a mismatch for beams at low energies. This mismatch can be very harmful for certain applications, for example the tomography diagnostic of the PITZ2 test line. In this case, the Twiss parameters at the start of the tomography section have to be as close as possible to the design ones. As can be shown by a thin lens approximation, all the Twiss parameters at the start of the tomography section are fully determined, as is the quadrupole strength, once the length of the FODO cells is chosen. With the presence of space charge it is necessary to introduce a modification to the original matching, itself performed with a standard optimizing routine. The idea is that this modification can only compensate for the linear part of space charge and it does so by changing the quadrupole strengths. The theory is verified by using an very simple test line consisting of just two quadrupoles and modeling it using GPT (General Particle Tracer). This results in modified values for the quadrupole strengths to accommodate the effect of space charge.  
 
WEPP120 G4Beamline Particle Tracking in Matter-dominated Beam Lines simulation, collider, target, antiproton 2776
 
  • T. J. Roberts, K. B. Beard
    Muons, Inc, Batavia
  • S. Ahmed, D. M. Kaplan, L. K. Spentzouris
    Illinois Institute of Technology, Chicago, Illinois
  • D. Huang
    IIT, Chicago, Illinois
  Most computer programs that calculate the trajectories of particles in accelerators assume that the particles travel in an evacuated chamber. The development of muon beams, which are needed for future facilities such as muon colliders and neutrino factories, is limited by the lack of user-friendly numerical simulation codes that accurately calculate scattering and energy loss in matter. Geant4 is an internationally supported tracking toolkit that was developed to simulate particle interactions in large detectors for high energy physics experiments, and includes most of what is known about the interactions of particles and matter. Geant4 has been partially adapted in a program called G4beamline to develop muon beam line designs. We are continuing the development of G4beamline to enhance its graphical user-interface and add other features to the program to facilitate its use by a larger set of beam line and accelerator developers.  
 
WEPP137 Accelerating and Transporting Attosecond and Femtosecond Bunches of Electrons electron, laser, cathode, vacuum 2815
 
  • V. A. Papadichev
    LPI, Moscow
  Dynamics of short bunches of electrons obtained upon field emission in a quasi-static electric field and a variable electric field of a laser has been studied*. The equation of longitudinal motion of electrons was numerically integrated. Emitted electrons are accelerated by quasi-static potential applied to the spike and this drastically reduces initial energy spread in the bunch preventing its fast elongation. When the forces of space charge have little effect, grouping part of the beam due to velocity spread acquired in the laser field permits to obtain bunches of about 200-as duration when using a carbon dioxide laser and about 6-as with a neodymium laser. Analytical models were used to evaluate the influence of the space charge of the bunch on the longitudinal motion of electrons in it. It has been shown that the proper choice of the intensities of both fields can cancel such an influence. There have been considered methods of lateral focusing of the beam taking into account possible initial angular divergence and space charge effects. Such electron bunches could be used directly in experiments or for generation of short pulses of coherent UV- and X-ray radiation.

*V. A. Papadichev, Femtosecond and Attosecond Bunches of Electrons Upon Field Emission in a Combined Quasi-static and Laser Electric Field, submitted to this Conference.

 
 
WEPP149 Advances in Parametric-resonance Ionization Cooling resonance, emittance, coupling, betatron 2838
 
  • Y. S. Derbenev
    Jefferson Lab, Newport News, Virginia
  • R. P. Johnson
    Muons, Inc, Batavia
  Parametric-resonance ionization cooling (PIC) is a muon-cooling technique that is useful for low-emittance muon colliders. This method requires a well-tuned focusing channel that is free of chromatic and spherical aberrations. The dispersion function of the channel must be large where the correction magnets are placed for aberration control but small and non-zero where the ionization cooling beryllium wedges are located to provide emittance exchange to maintain small momentum spread. In order to be of practical use in a muon collider, it also necessary that the focusing channel be as short as possible to minimize muon loss due to decay. A compact PIC focusing channel is described in which new magnet concepts are used to generate the required lattice functions.  
 
THYM02 Incoherent Effects of Space Charge and Electron Cloud resonance, incoherent-effects, beam-losses, emittance 2942
 
  • G. Franchetti, I. Hofmann
    GSI, Darmstadt
  • F. Zimmermann
    CERN, Geneva
  Trapping in, or scattering off, resonances driven by space charge or electron cloud in conjunction with synchrotron motion can explain numerous observations of slow beam loss and emittance growth, which are often accompanied by changes in the longitudinal beam profile. This talk will review recent progress in understanding and modelling the underlying mechanisms, highlight the differences and similarities between space charge and electron cloud, and discuss simulation results in the light of experimental observations, e.g., at GSI, CERN and BNL.  
slides icon Slides  
 
THYM03 Advanced Computing Tools and Models for Accelerator Physics simulation, electron, linac, collider 2947
 
  • R. D. Ryne
    LBNL, Berkeley, California
  The design of the next generation of accelerators will require a new level of simulation capability to perform high resolution, multi-physics modelling of beam dynamics phenomena and to design complex 3D electromagnetic structures. Thanks to the availability of computational resources that will soon reach the petascale, we will be able to perform simulations involving unprecedented size, complexity, and physical realism. This paper will review the state-of-the-art in scientific computing for accelerator physics.  
slides icon Slides  
 
THPC012 Longitudinal Beam Dynamics Studies for the FERMI@ELETTRA Linac linac, klystron, electron, emittance 2999
 
  • O. Ferrando, G. D'Auria
    ELETTRA, Basovizza, Trieste
  FERMI is a single-pass FEL project under construction at Sincrotrone Trieste Laboratory. It will be driven by the present warm S-band linac, upgraded by the addition of seven accelerating sections to bring its working energy up to 1.2 GeV. The goal of the project is to have an X-ray user facility covering the wavelength region between 100 -10 nm. The stringent constraints on the electron beam parameters required by FERMI, such as emittance, pulse to pulse energy and current stabilities, and time of arrival of the bunch at the input of the undulator chain, impose very stringent requirements on the parameters and operating conditions of the linac accelerating sections. To address the problem, i.e. evaluating the operating conditions of the machine and the flexibility of the adopted layout, beam dynamics studies with the LiTrack code have been performed. Here the results of different linac settings as well as the allowed variations in terms of RF phase and amplitude of the accelerating field are presented and discussed.  
 
THPC013 Start to End Simulations of Transverse to Longitudinal Emittance Exchange at the A0 Photoinjector emittance, simulation, radiation, synchrotron 3002
 
  • R. P. Fliller, H. T. Edwards, J. Ruan
    Fermilab, Batavia, Illinois
  • T. W. Koeth
    Rutgers University, The State University of New Jersey, Piscataway, New Jersey
  Various schemes to exchange the transverse and longitudinal emittance have been proposed (Cornacchia and Emma, Kim et.al). One scheme involves a deflecting mode RF cavity between two doglegs to exchange the horizontal and longitudinal emittances. This will produce a complete and uncoupled emittance exchange in the thin cavity limit using first order matrix optics. Various other effects, such as a finite length cavity, can leave the emittances coupled after the exchange and dilute the final emittances. Other effects such as space charge and synchrotron radiation can only be investigated through simulations. An exchange experiment is underway at the A0 Photoinjector at Fermilab. In this paper we present start to end simulations of the experiment using various codes to account for space charge and Coherent Synchrotron Radiation effects. Astra is used to simulate all of the straight sections, including the deflecting mode RF cavity. CSR track simulates the doglegs, and the spectrometer. The results of these simulations are compared with analytical approximations and preliminary data. The effect on the exchange is also discussed.  
 
THPC069 Impact of Magnet Misalignment in an ERL for Electron Cooling in RHIC emittance, electron, dipole, linac 3146
 
  • V. H. Ranjbar, D. T. Abell, K. Paul
    Tech-X, Boulder, Colorado
  • I. Ben-Zvi, J. Kewisch
    BNL, Upton, Long Island, New York
  • R. D. Ryne
    LBNL, Berkeley, California
  The MaryLie/IMPACT code was recently upgraded to include magnet errors. We have used the code to assess the sensitivity of final emittance of an ERL injector for the proposed RHIC electron cooler to up-stream magnetic element misalignments. This calculation will help determine the error tolerance for the construction of the ERL.  
 
THPC083 Simulation Studies of Space-charge Effects in the LENS Nonlinear Transport Lines octupole, simulation, target, focusing 3179
 
  • M. Hess, A. Bogdanov
    IUCF, Bloomington, Indiana
  The upgraded IUCF LENS beamline is designed to deliver a square shaped 13 MeV proton beam at 25 mA with a relatively uniform density using two octupole magnets for nonlinear focusing in both transverse directions. The space-charge effects in the LENS beamline (without nonlinear focusing) can vary the beam profile by roughly 8%-13% compared to a zero current beam. In this paper, we show the results of simulation studies of the LENS beamline which incorporate the effects of space-charge, as well as, nonlinear focusing from the octupole magnets. The simulations utilize self-consistent methods for computing the space-charge fields, since the beam density distribution can be nonlinear. We also show simulation results for beam currents in excess of 25 mA, which may be useful for future upgrades of LENS.  
 
THPC084 Studies of Electromagnetic Space-charge Fields in RF Photocathode Guns emittance, gun, simulation, cathode 3182
 
  • C. S. Park, M. Hess
    IUCF, Bloomington, Indiana
  In high-brightness rf photocathode guns, the effects of space-charge can be important. In an effort to accurately simulate the effects of these space-charge fields without the presence of numerical grid dispersion, a Green’s function based code called IRPSS (Indiana Rf Photocathode Source Simulator) was developed*. In this paper, we show the results of numerical simulations of the Argonne Wakefield Accelerator photocathode gun using IRPSS, and compare them with the results of an electrostatic based simulation code. In addition, we show how electromagnetic space-charge fields can affect the designs of photocathode gun magnetic focusing schemes, such as emittance compensation. We will also show how a multipole moment method can be effectively utilized to compute the reflections of electromagnetic space-charge fields due to irises in photocathode guns.

*M. Hess, C. S. Park, and D. Bolton. Phys. Rev. ST Accel. Beams 10, 054201 (2007).

 
 
THPC086 Transverse Mismatch Oscillations of a Bunched Beam in Presence of Space Charge and External Nonlinearities emittance, simulation, synchrotron, lattice 3188
 
  • C. Benedetti, G. Turchetti
    Bologna University, Bologna
  • G. Franchetti, I. Hofmann
    GSI, Darmstadt
  The damping of transverse mismatch oscillations depends on the combined effect of space charge as well as external nonlinearities. Previous studies of this problem for high intensity beams in a synchrotron have not included the combined effect of synchrotron oscillation and external nonlinearities on mismatch. In this paper we explore by 2.5D particle in cell simulations the effect on emittance growth, halo and beam loss caused by space charge, synchrotron oscillation and external nonlinearities. Different tunes are considered in order to understand the importance of external nonlinearities as function of the distance of the working point from the resonance condition.  
 
THPC091 Experimental Study of an Intense Relativistic Helical Electron Beam Formed with Interception of the Electrons Reflected from the Magnetic Mirror electron, gun, cathode, radiation 3200
 
  • E. V. Ilyakov, I. S. Kulagin, S. V. Kuzikov, A. S. Shevchenko
    IAP/RAS, Nizhny Novgorod
  • V. N. Manuilov
    NNGU, Nizhny Novgorod
  A new method of formation of pulsed intense relativistic helical electron beams (HEBs) for gyroresonant devices has been presented. The method is aimed at the increase of pitch-factor and the reduction of HEB velocity spread and is intended for use in the formation systems of laminar HEBs characterized by low influence of space charge on their parameters. The method is based on the operation of a special diaphragm located at one of minima of trajectories at the beginning of the transportation channel. The diaphragm diameter is chosen so that the electrons with the lowest oscillatory velocities cannot bend round the diaphragm and settle on it. The rest electrons pass by moving in the increasing magnetic field. Then, the electrons with the greatest oscillatory velocities are adiabatically reflected from the magnetic mirror between the electron gun and the transportation channel and settle on the back of the same diaphragm. Reduction of space charge of the reflected electrons has led to the increase of HEB pitch-factor (HEBs have been formed with the record of pitch-factors exceeding 2), while the accumulation of space charge worsens the HEB provoking modulation of formed HEB current.  
 
THPC100 Collisionless Relaxation in the Transport of Space Charge Dominated Beams simulation, focusing, resonance, plasma 3209
 
  • R. Pakter, Y. Levin, T. N. Teles
    IF-UFRGS, Porto Alegre
  Relaxation to a final stationary state of particles interacting through long-range forces, such as Coulomb, is intrinsically different than that of systems with short-range interactions. While in the latter case it is known that the interparticle collisions drive the system to an equilibrium Maxwell-Boltzmann distribution, in the former case, the collision duration time diverges and the state of thermodynamic equilibrium is never reached. In this paper, a theory is presented which allows to quantitatively predict the final stationary state achieved by a transported space-charge dominated beam during a process of collisionless relaxation*. It is shown that a fully matched beam relaxes to a Fermi-Dirac distribution. However, when a mismatch is present and the beam oscillates, halo formation leads to a phase separation. The theory developed allows to quantitatively predict both the density and the velocity distributions in the final stationary state, including the halo.

* Y. Levin, R. Pakter, and T. N. Teles, Phys. Rev. Lett., 100, 040604 (2008).

 
 
THPC101 Transverse Schottky Noise and Beam Transfer Functions with Space Charge ion, emittance, synchrotron, heavy-ion 3212
 
  • S. Paret, O. Boine-Frankenheim, V. Kornilov
    GSI, Darmstadt
  • T. Weiland
    TEMF, Darmstadt
  The heavy ion synchrotron SIS18 will serve as booster for the synchrotron SIS100 to be built as part of the Facility for Antiproton and Ion Research (FAIR). As such the SIS18 should accelerate ion beams with a factor of 10-100 higher intensity, compared to the present performance. Beams of such intensities may suffer instabilities due to collective effects. Particularly at injection-energy space charge and the resistive wall impedance will affect the beam remarkably. Experiments for the investigation of direct space charge were performed in SIS18. Transverse Schottky signals and beam transfer functions (BTF) of coasting ion beams affected by space charge were measured. A distortion of the Schottky bands and BTF was observed and compared to a simple model allowing for linear space charge. The model reproduced the deformation and yielded parameters of the beam.  
 
THPC103 Wave Breaking and Test Particle Dynamics in Inhomogeneous Beams emittance, simulation, focusing, plasma 3218
 
  • F. B. Rizzato, Y. Levin, R. P. Nunes, R. Pakter, E. G. Souza
    IF-UFRGS, Porto Alegre
  This work analyzes the dynamics of inhomogeneous, magnetically focused high-intensity beams of charged particles. While for homogeneous beams the whole system oscillates with a single frequency, any inhomogeneity leads to propagating transverse density waves which eventually result in a singular density build up, causing wave breaking and jet formation. Wave breaking is shown to relax the mismatched beam and we make use of Lynden-Bell's theory of violent relaxation to estimate characteristics of the relaxed state.  
 
THPC111 Simulation ofμBunching Instability Regimes in the FLASH Bunch Compressors bunching, simulation, gun, linac 3236
 
  • M. Vogt, T. Limberg
    DESY, Hamburg
  • D. H. Kuk
    The University of Texas at Austin, Austin, Texas
  The bunch compression scheme for the European XFEL will operate in a regime in which, at least without additional energy spread introduced by a laser heater, theμbunching effect proposed in the literature may severely degrade the performance of the FEL. However, clear, unambiguous signals of theμbunching effect have not yet been seen neither in simulation nor experiment. The proposedμbunching effect amplifies initial current modulations by interleaved application of longitudinal collective energy kicks and transformations of energy modulation into current modulation in magnetic chicanes. In order to establish a parameter regime for experimental verification ofμbunching at the FLASH VUV-FEL at DESY, we have scanned the relevant part of the parameter space using a linear, quasi-analytic, noise-free gain-model and complemented this with particle tracking simulations. The tracking was performed using interleaved runs of ASTRA for acceleration modules and CSRTrack for the chicanes, automatically linked by the start-to-end simulation tool box Gluetrack.  
 
THPP083 Megawatt Upgrades for the ISIS Facility linac, synchrotron, injection, target 3554
 
  • J. W.G. Thomason, D. J. Adams, D. J.S. Findlay, I. S.K. Gardner, B. Jones, A. P. Letchford, S. J. Payne, B. G. Pine, A. Seville, C. M. Warsop, R. E. Williamson
    STFC/RAL/ISIS, Chilton, Didcot, Oxon
  • D. C. Plostinar, C. R. Prior, G. H. Rees
    STFC/RAL/ASTeC, Chilton, Didcot, Oxon
  ISIS is the spallation neutron source at the Rutherford Appleton Laboratory in the UK. Presently, it runs at beam powers of 0.2 MW, with upgrades in place to supply increased powers for the new Second Target Station due to start operation in autumn 2008. This paper outlines schemes for major upgrades to the facility in the megawatt regime, with options for 1, 2 and 5 MW. The ideas centre around new 3.2 GeV RCS designs that can be employed to increase the energy of the existing ISIS beam to provide powers of ~1 MW or, possibly as a second upgrade stage, accumulate and accelerate beam from a new 0.8 GeV linac for 2-5 MW beams. Summaries of ring designs are presented, along with studies and simulations to assess the key loss mechanisms that will impose intensity limitations. Important factors include injection, RF systems, instabilities, longitudinal and transverse space charge.  
 
THPP084 Discussion on RCS versus AR on the Basis of J-PARC Beam Commissioning for Pulsed Spallation Neutron Source injection, beam-losses, linac, proton 3557
 
  • Y. Yamazaki
    KEK/JAEA, Ibaraki-Ken
  • M. Kinsho
    JAEA/J-PARC, Tokai-Mura, Naka-Gun, Ibaraki-Ken
  Over a decade it is one of the most controversial issues regarding the accelerator scheme choice whether RCS or AR should be chosen for the pulsed spallation neutron source. In order to simplify the discussion, we compare 3-GeV RCS with 1-GeV AR. The former is J-PARC scheme while the latter is SNS scheme. To summarize the discussion, RCS technology is much more difficult than AR technology, although RCS has many advantages over AR arising from its low beam current for the same beam power. Now, the J-PARC 3-GeV RCS was actually commissioned. On the basis of its experience, the discussion will be resumed.