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photon

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OPR03 Can Electron Multipacting Explain the Pressure Rise in the Cold Bore ANKA Superconducting Undulator? electron, vacuum, undulator, simulation 12
 
  • S. Casalbuoni, S. Schleede, M. Hagelstein, D. Saez de Jauregui, P. Tavares
    Karlsruhe Institute of Technology
  Preliminary studies performed with the cold bore superconducting undulator installed in the ANKA (Angstrom source Karlsruhe) storage ring suggest that the beam heat load is mainly due to the electron wall bombardment. Electron bombardment can both heat the cold vacuum chamber and induce an increase in the pressure because of gas desorption. In this contribution we compare the measurements of the pressure in a cold bore performed in the electron storage ring ANKA with the predictions obtained using the equations of gas dynamic balance in a cold vacuum chamber exposed to synchrotron radiation and electron bombardment. The balance results from two competing effects: the photon and electron stimulated desorption of the gas contained in the surface layer of the chamber wall and of the gas cryosorbed, and the cryopumping by the cold surface. We show that photodesorption alone cannot explain the experimental results and that electron multipacting is needed to reproduce the observed pressure rise. Electron bombardment can at the same time explain the observed beam heat load.  
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PST03 Methods for Quantitative Interpretation of Retarding Field Analyzer Data simulation, electron, positron, pick-up 91
 
  • J. Calvey, J. Crittenden, G. Dugan, M. Palmer
    Cornell University - CLASSE
  • K. Harkay
    Argonne National Laboratory
  A great deal of Retarding Field Analyzer (RFA) data has been taken as part of the CesrTA program at Cornell. Obtaining a quantitative understanding of this data requires use of cloud simulation programs, as well as a detailed model of the RFA itself. In some cases the RFA can be modeled by postprocessing the output of a simulation codes, and one can obtain “best fit” values for important simulation parameters using a systematic method to improve agreement between data and simulation. In other cases, in particular in high magnetic field regions, the presence of the RFA can have an effect on the cloud, and one needs to include a model of the RFA in the simulation program itself.  
 
PST08 Synrad3D Photon Propagation and Scattering Simulation vacuum, site, scattering, radiation 118
 
  • G. Dugan, D. Sagan
    Cornell University - CLASSE
  As part of the Bmad software library, a program called Synrad3d has been written to track synchrotron radiation photons generated in storage rings. The purpose of the program is primarily to estimate the intensity and distribution of photon absorption sites, which are critical inputs to codes which model the growth of electron clouds. Synrad3d includes scattering from the vacuum chamber walls using X-ray data from an LBNL database. Synrad3d can handle any planar lattice and a wide variety of vacuum chamber profiles. A description of the program will be given, together with some examples of results.  
 
PST10 Using Coherent Tune Shifts to Evaluate Electron Cloud Effects on Beam Dynamics at CesrTA simulation, positron, electron, dipole 130
 
  • D. Kreinick, J. Crittenden, G. Dugan, Z. Leong, M. Palmer
    Cornell University - CLASSE
  • R. Holtzapple, M. Randazzo
    California Polytechnic State University
  • M. Furman, M. Venturini
    LBNL
  One technique used at CesrTA for studying the effects of electron clouds on beam dynamics is to measure electron and positron bunch tunes under a wide variety of beam energies, bunch charge, and bunch train configurations. Comparing the observed tunes with the predictions of various simulation programs allows the evaluation of important parameters in the cloud formation models. These simulations will be used to predict the behavior of the electron cloud in damping rings for future linear colliders.  
 
MOD01 Analysis of Synchrotron Radiation using SYNRAD3D and Plans to Create a Photoemission Model wiggler, radiation, electron, damping 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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FTR00 ILC Damping Rings: Benefit of the Antechamber or: Antechamber vs. SEY electron, simulation, positron, dipole 194
 
  • M. Furman
    LBNL
  We review the simulation results for the electron cloud build-up for the ILC Damping Rings, for both lattice options considered (6 km and 3 km), in a field-free region and in a bending dipole magnet. While the 6 km lattice is slightly more forgiving than the 3-km lattice vis-a-vis the electron cloud effects, we conclude that, in general, the existence of an antechamber helps to dramatically reduce the electron-cloud density (factor ~50) only if the peak secondary yield of the chamber surface is below a certain critical value. This critical value is in the range ~1.1~1.3, depending on various details.  
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