Author: Yin Vallgren, C.
Paper Title Page
TUPS027 Characterization of Carbon Coatings with Low Secondary Electron Yield 1587
 
  • C. Yin Vallgren, S. Calatroni, P. Costa Pinto, A. Kuzucan, H. Neupert, M. Taborelli
    CERN, Geneva, Switzerland
 
  Amorphous carbon (a-C) coatings can reliably be produced with a maximum secondary electron yield (SEY) close to 1 at room temperature. Measurements at low temperature (LHe) are in progress. Analysis by X-ray Photoemission Spectroscopy (XPS) shows a correlation between the lineshape of C1s spectrum in XPS and maximum SEY of the investigated samples. The initial level of oxygen on the surface of the various samples does not seem to be related to the initial maximum SEY value. However, the increase of the SEY with air exposure time on each individual sample is related to the amount of oxygen containing adsorbates. Storage in different environments has been investigated (static vacuum, aluminum foil, dry nitrogen and desiccators) and shows significant differences in the “aging” behavior. Aging is very moderate when storing samples wrapped in aluminum foil in air. Samples which have undergone aging due to inappropriate storage can be recovered nearly to the initial value of the SEY by typical surface treatments as ion bombardment, annealing under vacuum and conditioning by electron beam. However, an enhanced sensitivity to air exposures is observed for most of these curing methods.  
 
TUPS028 Performance of Carbon Coating for Mitigation of Electron Cloud in the SPS 1590
 
  • C. Yin Vallgren, P. Chiggiato, P. Costa Pinto, H. Neupert, G. Rumolo, E.N. Shaposhnikova, M. Taborelli
    CERN, Geneva, Switzerland
 
  Amorphous carbon (a-C) coatings have been tested in electron cloud monitors (ECM) in the Super Proton Synchrotron (SPS) and have shown for LHC type beams a reduction of the EC current by a factor 104 compared to stainless steel (SS). This performance has been maintained for more than 2 years under SPS operation conditions. Secondary electron yield (SEY) laboratory data confirm that after 1 year of SPS operation, the coating maintains a SEY below 1. The compatibility of coexisting SS and a-C surfaces has been studied in an ECM having coated and uncoated areas. The results show no degradation of the properties of the a-C areas. The performance of diamond like carbon (DLC) coating has also been studied. DLC shows a less effective reduction of the EC current than a-C, but conditioning is faster than for SS. Three a-C coated dipoles were inserted in the SPS. However, even with no EC detected, the dynamic pressure rise is similar to the one observed in the SS reference dipoles. Measurement in a new ECM equipped with clearing electrodes to verify the relation between pressure signals and intensity of the EC, as well as an improvement of the diagnostics in the dipoles are in progress.  
 
TUPC030 Recommendation for Mitigations of the Electron Cloud Instability in the ILC 1063
 
  • M.T.F. Pivi, L. Wang
    SLAC, Menlo Park, California, USA
  • L.E. Boon, K.C. Harkay
    ANL, Argonne, USA
  • J.A. Crittenden, G. Dugan, M.A. Palmer
    CLASSE, Ithaca, New York, USA
  • T. Demma, S. Guiducci
    INFN/LNF, Frascati (Roma), Italy
  • M.A. Furman
    LBNL, Berkeley, California, USA
  • K. Ohmi, K. Shibata, Y. Suetsugu, J. Urakawa
    KEK, Ibaraki, Japan
  • C. Yin Vallgren
    Chalmers University of Technology, Chalmers Tekniska Högskola, Gothenburg, Sweden
 
  Funding: Work supported by the Director, Office of Science, High Energy Physics, U.S. DOE under Contract No. DE-AC02-76SF00515.
Electron cloud has been identified as one of the highest priority issues for the ILC Damping Rings (DR). A working group has evaluated the electron cloud effect and instability, and mitigation solutions for the electron cloud formation. Working group deliverables include recommendations for the baseline and alternate solutions for the electron cloud mitigation in various regions of the ILC Positron DR, which is presently assumed to be the 3.2km design. Detailed studies of a range of mitigation options including coatings, clearing electrodes, grooves and novel concepts, were carried out over the previous several years by nearly 50 researchers, and the results of the studies form the basis for the recommendation. The assessments of the benefits or risks associated with the various options were based on a systematic ranking scheme. The recommendations are the result of the working group discussions held at numerous meetings and during a dedicated workshop. The mitigation choices will be also presented in a more detailed report later in 2012. In addition, a number of items requiring further investigation were identified and studies will be carried out at CesrTA and other institutions.