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Vay, J.-L.

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TUXAB01 Absolute Measurement of Electron Cloud Density 754
  • M. Kireeff Covo, R. H. Cohen, A. Friedman, A. W. Molvik
    LLNL, Livermore, California
  • D. Baca, F. M. Bieniosek, B. G. Logan, P. A. Seidl, J.-L. Vay
    LBNL, Berkeley, California
  • J. L. Vujic
    UCB, Berkeley, California
  Funding: This work was supported by the Director, Office of Science, Office of Fusion Energy Sciences, of the U. S. Department of Energy, LLNL and LBNL, under contracts No. W-7405-Eng-48 and DE-AC02-05CH11231.

Beam interaction with background gas and walls produces ubiquitous clouds of stray electrons that frequently limit the performance of particle accelerator and storage rings. Counterintuitively we obtained the electron cloud accumulation by measuring the expelled ions that are originated from the beam-background gas interaction, rather than by measuring electrons that reach the walls. The kinetic ion energy measured with a retarding field analyzer (RFA) maps the depressed beam space-charge potential and provides the dynamic electron cloud density. Clearing electrode current measurements give the static electron cloud background that complements and corroborates with the RFA measurements, providing an absolute measurement of electron cloud density during a 5 us duration beam pulse in a drift region of the magnetic transport section of the High-Current Experiment (HCX) at LBNL.*

* M. Kireeff Covo, A. W. Molvik, A. Friedman, J.-L. Vay, P. A. Seidl, G. Logan, D. Baca, and J. L. Vujic, Phys. Rev. Lett. 97, 054801 (2006).

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TUXAB03 Self-consistent 3D Modeling of Electron Cloud Dynamics and Beam Response 764
  • M. A. Furman, C. M. Celata, M. Kireeff Covo, K. G. Sonnad, J.-L. Vay, M. Venturini
    LBNL, Berkeley, California
  • R. H. Cohen, A. Friedman, D. P. Grote, A. W. Molvik
    LLNL, Livermore, California
  • P. Stoltz
    Tech-X, Boulder, Colorado
  Funding: Work supported by the U. S. DOE under Contracts DE-AC02-05CH11231 and W-7405-Eng-48, and by the US-LHC Accelerator Research Project (LARP).

We present recent advances in the modeling of beam-electron-cloud dynamics, including surface effects such as secondary electron emission, gas desorption, etc, and volumetric effects such as ionization of residual gas and charge-exchange reactions. Simulations for the HCX facility with the code WARP/POSINST will be described and their validity demonstrated by benchmarks against measurements. The code models a wide range of physical processes and uses a number of novel techniques, including a large-timestep electron mover that smoothly interpolates between direct orbit calculation and guiding-center drift equations, and a new computational technique, based on a Lorentz transformation to a moving frame, that allows the cost of a fully 3D simulation to be reduced to that of a quasi-static approximation.

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TUPMN108 Particle-in-Cell Calculations of the Electron Cloud in the ILC Positron Damping Ring Wigglers 1164
  • C. M. Celata, M. A. Furman, J.-L. Vay
    LBNL, Berkeley, California
  • D. P. Grote
    LLNL, Livermore, California
  Funding: This work was supported by the Office of High Energy Physics of the U. S. Department of Energy under contract number No. DE-AC02-05CH11231.

Due to copious synchrotron radiation from the beam, electron cloud effects are predicted to be important in the wiggler sections of the ILC positron damping ring. In this area of the ring, the physics is inherently 3D. Moreover, a self-consistent calculation of the physics of the electron cloud/beam system is necessary for examining such phenomena as emittance growth in the beam. We present the first calculations of this system with the self-consistent 3D particle-in-cell code WARP/POSINST. The code includes self-consistent space charge for both species, mesh refinement, and detailed models of primary and secondary electron production. Interaction with electrons is assumed to occur only in the wigglers in this model– the beam is moved using maps between wiggler sections.

THPMN118 Modelling of E-cloud Build-up in Grooved Vacuum Chambers Using POSINST 2993
  • M. Venturini, M. A. Furman, J.-L. Vay
    LBNL, Berkeley, California
  • M. T.F. Pivi
    SLAC, Menlo Park, California
  Funding: Work supported by DOE contract No. DE-AC02-05CH11231

Electron cloud build-up and related beam instabilities are a serious concern for the positron damping ring of the International Linear Collider (ILC). To mitigate the effect use of grooved vacuum-chamber walls is being actively investigated in addition to more conventional techniques like surface coating, scrubbing, and/or conditioning. Experimental and simulation studies have characterized the effectiveness of the grooved surface by means of an effective secondary emission yield (SEY), which has been measured to be significantly lower than the SEY of a smooth surface of the same material. However, some inconsistencies of the results, and the need to model the experimental testing of the grooved surface concept in more detail, have motivated us to simulate the grooved surfaces directly. Specifically, we have augmented the code POSINST by adding the option to simulate the electron-cloud build-up in the presence of a grooved surface geometry. By computing the accumulated e-cloud density and comparing it with the same quantity computed for a smooth surface, we infer an effective SEY, and we thereby make contact with the effective SEY estimates obtained from previous studies.

THPAS050 Simulating Electron Effects in Heavy-Ion Accelerators with Solenoid Focusing 3603
  • W. M. Sharp, R. H. Cohen, A. Friedman, D. P. Grote, A. W. Molvik
    LLNL, Livermore, California
  • J. E. Coleman, P. K. Roy, P. A. Seidl, J.-L. Vay
    LBNL, Berkeley, California
  • I. Haber
    UMD, College Park, Maryland
  Funding: This work was performed under the auspices of US DOE by the University of California Lawrence Livermore and Lawrence Berkeley National Laboratories under contracts W-7405-Eng-48 and DE-AC03-76SF00098.

Contamination from electrons is a concern for solenoid-focused ion accelerators being developed for experiments in high-energy-density physics (HEDP). These electrons, produced directly by beam ions hitting lattice elements or indirectly by ionization of desorbed neutral gas, can potentially alter the beam dynamics, leading to a time-varying focal spot, increased emittance, halo, and possibly electron-ion instabilities. The electrostatic particle-in-cell code WARP is used to simulate electron-cloud studies on the solenoid-transport experiment (STX) at Lawrence Berkeley National Laboratory. We present self-consistent simulations of several STX configurations to show the evolution of the electron and ion-beam distributions first in idealized 2-D solenoid fields and then in the 3-D field values obtained from probes. Comparisons are made with experimental data, and several techniques to mitigate electron effects are demonstrated numerically.

FRPMS028 Simulations of Electron Cloud Effects on the Beam Dynamics for the FNAL Main Injector Upgrade 3985
  • K. G. Sonnad, C. M. Celata, M. A. Furman, D. P. Grote, J.-L. Vay, M. Venturini
    LBNL, Berkeley, California
  Funding: Work supported by the U. S. DOE under Contract no. DE-AC02-05CH11231.

The Fermilab main injector (MI) is being considered for an upgrade as part of the high intensity neutrino source (HINS) effort. This upgrade will involve a significant increasing of the bunch intensity relative to its present value. Such an increase will place the MI in a regime in which electron-cloud effects are expected to become important. We have used the electrostatic particle-in-cell code WARP, recently augmented with new modeling capabilities and simulation techniques, to study the dynamics of beam-electron cloud interaction. This study involves a systematic assesment of beam instabilities due to the presence of electron clouds.

THPAN075 Modeling Incoherent Electron Cloud Effects 3393
  • F. Zimmermann, E. Benedetto, G. Rumolo, D. Schulte, R. Tomas
    CERN, Geneva
  • W. Fischer
    BNL, Upton, Long Island, New York
  • G. Franchetti
    GSI, Darmstadt
  • K. Ohmi
    KEK, Ibaraki
  • M. T.F. Pivi, T. O. Raubenheimer
    SLAC, Menlo Park, California
  • K. G. Sonnad, J.-L. Vay
    LBNL, Berkeley, California
  Incoherent effects driven by an electron cloud could seriously limit the beam lifetime in proton storage rings or blow up the vertical emittance in positron ones. Different approaches to modeling these effects each have their own merits and drawbacks. We compare the simulation results and computing time requirements from a number of dedicated codes under development over the last years, and describe the respective approximations for the beam-electron cloud interaction, the accelerator structure, and the optical lattice, made in each of these codes. Examples considered include the LHC, CERN SPS, RHIC, and the ILC damping ring. Tentative conclusions are drawn and a strategy for further codes development is outlined.  
THPAS031 Measurement and Simulation of Source-Generated Halos in the University of Maryland Electron Ring (UMER) 3564
  • I. Haber, S. Bernal, R. Feldman, R. A. Kishek, P. G. O'Shea, C. Papadopoulos, M. Reiser, D. Stratakis, M. Walter
    UMD, College Park, Maryland
  • A. Friedman, D. P. Grote
    LLNL, Livermore, California
  • J.-L. Vay
    LBNL, Berkeley, California
  Funding: This work is supported by the US DOE under contract Nos. DE-FG02-02ER54672 and DE-FG02-94ER40855 (UMD), and DE-AC02-05CH11231 (LBNL) and W-7405-ENG-48 (LLNL)

One of the areas fundamental beam physics that serve as the rationale for recent research on UMER is the study of generation and evolution of beam halos. This physics can be accessed on a scaled basis in UMER at a small fraction of the cost of similar experiments on a much larger machine. Recent experiments and simulations have identified imperfections in the source geometry, particularly in the region near the emitter edge, as a potentially significant source of halo particles. The edge-generated halo particles, both in the experiments and the simulations are found to pass through the center of the beam in the vicinity of the anode plane. Understanding the detailed evolution of these particle orbits is therefore important to designing any aperture to remove the beam halo. Both experimental data and simulations will be presented to illustrate the details of this mechanism for halo formation.