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Baglin, V.

Paper Title Page
TUPP027 Electron Energy Dependence of Scrubbing Efficiency to Mitigate E-cloud Formation in Accelerators 1592
 
  • R. Cimino, M. Commisso, T. Demma, A. G. Grilli, P. Liu, M. Pietropaoli, V. Sciarra
    INFN/LNF, Frascati (Roma)
  • V. Baglin
    CERN, Geneva
  • P. Barone, A. Bonanno
    INFN Gruppo di Cosenza, Arcavacata di Rende (Cosenza)
  
  Recently built and planned accelerators, base their ability to reach design parameters, on the capability to reduce Secondary Electron Yield (SEY) during commissioning, hence mitigating the potentially detrimental effects of e-cloud driven machine limitations. This SEY reduction (called "scrubbing"), is due to the fact that the electrons of the cloud, hit the vacuum chamber wall, modifying its surface properties and reducing its SEY. This minimise any disturbing effects of the e-cloud to the beam. "Scrubbing" has been studied only as a function of impinging electron dose. In reality SEY modifications are only studied by bombarding surfaces with 300-500 eV electrons, but no scrubbing dependence on the bombarding electron energy has ever been discussed. The actual energy of the electrons of the cloud hitting the wall in real accelerators has never been measured accurately, while simulations predict very low electron energies (<50 eV). For this reason and given the peculiar behaviour observed for low energy electrons*, we decided to study this dependence accurately. Here we present some preliminary results discussing eventual implications to machine commissioning procedures.

*R. Cimino et al. Phys. Rev. Lett 93, 14801 (2004).

 
WEPC103 Design of a Cold Vacuum Chamber for Diagnostics 2240
 
  • S. Casalbuoni, T. Baumbach, A. W. Grau, M. Hagelstein, R. Rossmanith
    FZK, Karlsruhe
  • V. Baglin, B. Jenninger
    CERN, Geneva
  • R. Cimino
    INFN/LNF, Frascati (Roma)
  • M. P. Cox
    Diamond, Oxfordshire
  • E. M. Mashkina
    University of Erlangen-Nürnberg, Physikalisches Institut II, Erlangen
  • E. J. Wallén
    MAX-lab, Lund
  • R. Weigel
    Max-Planck Institute for Metal Research, Stuttgart
  
  Preliminary studies performed with the cold bore superconducting undulator installed in the ANKA storage ring suggest that the beam heat load is mainly due to the electron wall bombardment. Low energy electrons (few eV) are accelerated by the electric field of the beam to the wall of the vacuum chamber, induce non-thermal outgassing from the cryogenic surface and heat the undulator. In this contribution we report on the design of a cold vacuum chamber for diagnostics to be installed in the ANKA (ANgstrom source KArlsruhe) storage ring and possibly in third generation light sources. The diagnostics implemented are:
  1. retarding field analyzers to measure the electron energy and flux,
  2. temperature sensors to measure the total heat load,
  3. pressure gauges,
  4. and a mass spectrometer to measure the gas content.
The aim of this device is to gain a deeper understanding on the heat load mechanisms to a cold vacuum chamber in a storage ring and find effective remedies. The outcome of the study is of relevance for the design and operation of cold bore superconducting insertion devices in synchrotron light sources. 		 
THPP138 Achievement and Evaluation of the Beam Vacuum Performance of the LHC Long Straight Sections 3685
 
  • G. Bregliozzi, V. Baglin, S. Blanchard, J. Hansen, J. M. Jimenez, K. Weiss
    CERN, Geneva
  
  The bake-out and activation of the 6 km Long Straight Sections (LSS) of the Large Hadron Collider (LHC) is in its final step. After bake-out and activation of the NEG coating, the average ultimate pressure, over more than one hundred vacuum sectors, is below 10-11 mbar. Therefore, the nominal requirement for the four experimental insertions is guaranteed. The nominal performances are also ensured for all the other insertions where collimators, RF cavities and beam dumping systems are present. The main difficulties encountered during the bake-out and activation of NEG coated chambers of the LSS vacuum sectors will be presented and discussed. In particular, the acceptance test and the limiting factors of the reached ultimate pressures will be addressed. Furthermore, the influence on the ultimate pressures of the beam vacuum elements (collimators, beam instrumentation, etc.) will be discussed. Finally, preliminary results obtained from a laboratory NEG pilot sector dedicated to the quality control of the LHC beam vacuum and to the evaluation of the NEG performance will be presented.