MOD  —  Electron Cloud Build-Up Modeling  

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MOD00 Electron Cloud Issues for the APS Superconducting Undulator  
 
  • K. Harkay, Y. Ivanyushenkov, R. Kustom, E. Moog, R. Rosenberg, E. Trakhtenberg
    Argonne National Laboratory
  • A. Garfinkel, L. Boon
    Purdue University
  • S. Casalbuoni
    Karlsruhe Institute of Technology
  
  The APS Upgrade calls for the development and commissioning of a superconducting undulator (SCU) at the Advanced Photon Source (APS), a 7-GeV electron synchrotron. Operation of an SCU at ANKA, also an electron ring, suggests that electron multipacting may in part be responsible for the observed heat load and pressure rise, but this effect is not predicted by an electron cloud generation code. It was found at APS that while the cloud code POSINST agreed fairly well with Retarding Field Analyzer (RFA) data for a positron beam (operated 1996-98), the agreement was less satisfactory for the electron beam. The APS data suggest that the photoelectron model is not complete. Given that the heat load is a critical parameter in designing the cryosystem for the SCU and given the experience at ANKA, a study is underway to minimize the possible contribution to the heat load by the electron cloud at APS, the photoelectrons in particular. In this talk, the results from POSINST are presented. Preliminary tracking of the photon flux using SYNRAD3D for the APS SCU chamber is presented, and possible ways to mitigate the photoelectrons are discussed.  
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MOD01 Analysis of Synchrotron Radiation using SYNRAD3D and Plans to Create a Photoemission Model 147
 
  • L. Boon, A. Garfinkel
    Purdue University
  • K. Harkay
    Argonne National Laboratory
  
  Electron cloud data from electron rings suggest that the photoelectron model in electron cloud generation codes is incomplete. The photoelectron model will be important in modeling the cloud generation on components downstream of wigglers, which can produce a very high photon flux on the wall in a local region. The code SYNRAD3D has been developed in the context of the Bmad accelerator physics software library. SYNRAD3D includes computation of synchrotron radiation and propagation in 3D through a vacuum chamber. The probability of reflection vs. absorption of the photons on the chamber wall is included, using data from the literature. We used SYNRAD3D to model the photon flux for the ILC damping ring. For simplicity in modeling, we started with a round chamber and varied parameters such as the number of simulation-generated photons, bin size, photon energy cutoff, and whether photons reflect off the wall. With a realistic photon flux and distribution, we can study models for the photoemission. Preliminary work has begun to develop a photoelectron model using Retarding Field Analyzer (RFA) data. The work to date and future plans are described.  
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MOD02 Electron Dynamics in the Wigglers of CESR-TA  
 
  • C. Celata
    LBNL
  
  Funding: This work was supported by the National Science Foundation under contract PHY-0734867 and the Office of Science, U. S. Department of Energy, under Contract No. DE-FC02-08ER41538.

Simulations of electron cloud buildup in the CESR-TA wigglers have been performed using the 3D code WARP-POSINST. The beam field is modeled using the Bassetti-Erskine electric field and does not evolve in time. The electron cloud distribution during the passage of a 45-bunch train has been examined with particular attention to the difference in dynamics at the z locations of the maximum and minimum vertical magnetic field, By. Near the z locations of the zeroes of By electrons near the chamber midplane cross field lines, driven by the gradient and curvature of the magnetic field, eventually reaching the vicinity of the beam. Near the maxima of By the cloud buildup is like that in a dipole, and this cloud spatial distribution occurs through much of the length of the wiggler period. This report will discuss these findings, delineate the areas of the wiggler in which each of these different behaviors occurs, and give results for the tune shift caused by the cloud in each area and for the whole wiggler period.

 
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MOD03 Accurate Simulation of the Electron Cloud in the Fermilab Main Injector with VORPAL 152
 
  • P. Lebrun, P. Spentzouris
    Fermilab
  • J. Cary
    University of Colorado Boulder
  • S. Veitzer, P. Stoltz
    Tech-X Corporation
  
  We present results from a precision simulation of the electron cloud (EC) problem in the Fermilab Main Injector using the code VORPAL. Fully 3D and self consistent that include both distributions of electrons in 6D phase-space and E. M. field maps. Various configurations of the magnetic fields found around the machine have been studied. Plasma waves associated to the fluctuation density of the cloud have been analyzed. Our results are compaired with those obtained with the POSINST code. It is shown that the 3D effects are important. The response of a Retarding Field Analyzer (RFA) to the EC has been simulated, as well as the more challenging microwave absorption experiment. Definite predictions of their exact response are difficult to compute, mostly because of the uncertainties in the secondary emission yield and, in the case of the RFA, because of the sensitivity of the electron collection efficiency to unknown stray magnetic fields. Nonetheless, our simulations do provide guidance to the experimental program.  
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MOD04 Modeling Electron Cloud Buildup and Microwave Diagnostics using VORPAL 162
 
  • S. Veitzer, P. Stoltz
    Tech-X Corporation
  • K. Sonnad
    Cornell University - CLASSE
  • P. Lebrun
    Fermilab
  
  We present an overview of recent electron cloud modeling results using the multi-dimensional, parallel, plasma simulation code VORPAL. We have used VORPAL to model cloud buildup in dipole, quadrupole, and field-free magnetic field configurations, in both circular and elliptical cross section pipes relevant to microwave diagnostics at the PEP-II experiment at SLAC, and ongoing experiments in the Main Injector at Fermilab. In addition, we present preliminary results for modeling electron orbits in the CesrTA wiggler, which is the beginning of a more detailed modeling effort to understand electron cloud effects in electron/positron accelerators, as well as connecting microwave side-band measurements to cloud densities. We also report on recent 3-Dimensional microwave transmission simulations through uniform and non-uniform clouds, and with higher order TE and TM waves using VORPAL.  
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MOD05 Trapping of Electron Cloud in ILC / CesrTA Quadrupole and Sextupole Magnets 167
 
  • M. Pivi, L. Wang
    SLAC National Accelerator Laboratory
  
  This talk will discuss the electron trapping mechanism in quadrupole and sextupole magnets. We will present the results in CESRTA and ILC quadrupole and sextupole magnets.  
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