HINS R&D Collaboration on Electron Cloud Effects: MidyearReport

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We present a report on ongoing activities on electron-cloud R&D for the MI upgrade. These results update and extend those presented in Refs. 1, 2. In this report we have significantly expanded the parameter range explored in bunch intensity Nb, RMS bunch length {sigma}{sub z} and peak secondary emission yield (SEY) {delta}{sub max}, but we have constrained our simulations to a field-free region. We describe the threshold behaviors in all of the above three parameters. For {delta}{sub max} {ge} 1.5 we find that, even for N{sub b} = 1 x 10{sup 11}, the electron cloud density, when averaged over the ... continued below

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Furman, M.A.; Sonnad, K. & Vay, J.-L. November 7, 2006.

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We present a report on ongoing activities on electron-cloud R&D for the MI upgrade. These results update and extend those presented in Refs. 1, 2. In this report we have significantly expanded the parameter range explored in bunch intensity Nb, RMS bunch length {sigma}{sub z} and peak secondary emission yield (SEY) {delta}{sub max}, but we have constrained our simulations to a field-free region. We describe the threshold behaviors in all of the above three parameters. For {delta}{sub max} {ge} 1.5 we find that, even for N{sub b} = 1 x 10{sup 11}, the electron cloud density, when averaged over the entire chamber, exceeds the beam neutralization level, but remains significantly below the local neutralization level (ie., when the electron density is computed in the neighborhood of the beam). This 'excess' of electrons is accounted for by narrow regions of high concentration of electrons very close to the chamber surface, especially at the top and bottom of the chamber, akin to virtual cathodes. These virtual cathodes are kept in equilibrium, on average, by a competition between space-charge forces (including their images) and secondary emission, a mechanism that shares some features with the space-charge saturation of the current in a diode at high fields. For N{sub b} = 3 x 10{sup 11} the electron cloud build-up growth rate and saturation density have a strong dependence on {sigma}{sub z} as {sigma}{sub z} decreases below {approx} 0.4 m, when the average electron-wall impact energy roughly reaches the energy E{sub max} where {delta} peaks. We also present improved results on emittance growth simulations of the beam obtained with the code WARP/POSINST in quasi-static mode, in which the beam-(electron cloud) interaction is lumped into N{sub s} 'stations' around the ring, where N{sub s} = 1, 2,..., 9. The emittance shows a rapid growth of {approx} 20% during the first {approx} 100 turns, followed by a much slower growth rate of {approx} 0.03%/turn. Concerning the electron cloud detection technique using microwave transmission, we present an improved dispersion relation for the TE mode of the microwaves, and a corresponding analytic estimate of the phase shift.

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  • Report No.: LBNL--61921
  • Grant Number: DE-AC02-05CH11231
  • DOI: 10.2172/922851 | External Link
  • Office of Scientific & Technical Information Report Number: 922851
  • Archival Resource Key: ark:/67531/metadc898608

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Office of Scientific and Technical Information (OSTI) is the Department of Energy (DOE) office that collects, preserves, and disseminates DOE-sponsored research and development (R&D) results that are the outcomes of R&D projects or other funded activities at DOE labs and facilities nationwide and grantees at universities and other institutions.

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  • November 7, 2006

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  • Sept. 27, 2016, 1:39 a.m.

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  • Sept. 29, 2016, 8:36 p.m.

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Furman, M.A.; Sonnad, K. & Vay, J.-L. HINS R&D Collaboration on Electron Cloud Effects: MidyearReport, report, November 7, 2006; Berkeley, California. (digital.library.unt.edu/ark:/67531/metadc898608/: accessed October 23, 2017), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.