4,758 research outputs found
Electron Cloud Effects in Accelerators
We present a brief summary of various aspects of the electron-cloud effect
(ECE) in accelerators. For further details, the reader is encouraged to refer
to the proceedings of many prior workshops, either dedicated to EC or with
significant EC contents, including the entire "ECLOUD" series [122]. In
addition, the proceedings of the various flavors of Particle Accelerator
Conferences [23] contain a large number of EC-related publications. The ICFA
Beam Dynamics Newsletter series [24] contains one dedicated issue, and several
occasional articles, on EC. An extensive reference database is the LHC website
on EC [25].Comment: 8 pages, contribution to the Joint INFN-CERN-EuCARD-AccNet Workshop
on Electron-Cloud Effects: ECLOUD'12; 5-9 Jun 2012, La Biodola, Isola d'Elba,
Ital
Summary of Session III
This is a summary of the talks presented in Session III ''Simulations of Electron-Cloud Build Up'' of the Mini-Workshop on Electron-Cloud Simulations for Proton and Positron Beams ECLOUD-02, held at CERN, 15-18 April 2002
Ecloud in PS2, PS+, SPS+
We present a preliminary but broad assessment of the ecloud build-up for the various proposed upgrades of the LHC and its injectors. The study pertains only to the ecloud in bending dipole magnets, and does not shed any light on the effects of the electrons on the beam. We focus on the ecloud heat load, although we have computed many other quantities of interest. The basic variable used to classify our results is the bunch spacing tb, whose values are 12.5, 25, 50 and 75 ns. The ecloud heat load follows an inverse relation to tb both for the LHC and for the injectors, with tb = 12.5 ns being by far the least favorable case. Although tb = 75 ns is the most favorable case, the 50-ns option comes closely behind. A simulated comparison of copper vs. stainless steel shows a clear advantage of the former over the latter. Somewhat surprisingly, a comparison of gaussian vs. flat longitudinal bunch profile does not show a clear winner, at least for the LHC at tb = 50 ns. We describe the strengths and limitations of our calculations
Formation of plasma around a small meteoroid: 1. Kinetic theory
This article is a companion to Dimant and Oppenheim [2017] https://doi.org/10.1002/2017JA023963.This paper calculates the spatial distribution of the plasma responsible for radar head echoes by applying the kinetic theory developed in the companion paper. This results in a set of analytic expressions for the plasma density as a function of distance from the meteoroid. It shows that at distances less than a collisional mean free path from the meteoroid surface, the plasma density drops in proportion to 1/R where R is the distance from the meteoroid center; and, at distances much longer than the meanâfreeâpath behind the meteoroid, the density diminishes at a rate proportional to 1/R2. The results of this paper should be used for modeling and analysis of radar head echoes.This work was supported by NSF grant AGS-1244842. (AGS-1244842 - NSF
Scalar resonances: scattering and production amplitudes
Scattering and production amplitudes involving scalar resonances are known,
according to Watson's theorem, to share the same phase . We show
that, at low energies, the production amplitude is fully determined by the
combination of with another phase , which describes
intermediate two-meson propagation and is theoretically unambiguous. Our main
result is a simple and almost model independent expression, which generalizes
the usual -matrix unitarization procedure and is suited to be used in
analyses of production data involving scalar resonances.Comment: 10 pages, 4 figures. Minor changes, references added, version to
appear in Phys. Rev.
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Electron Cloud Updated Simulation Results for the PSR, and Recent Results for the SNS
Recent simulation results for the main features of the electron cloud in the storage ring of the Spallation Neutron Source (SNS) at Oak Ridge, and updated results for the Proton Storage Ring (PSR) at Los Alamos are presented in this paper. A refined model for the secondary emission process including the so called true secondary, rediffused and backscattered electrons has recently been included in the electron-cloud code
Orbit equivalence rigidity for ergodic actions of the mapping class group
We establish orbit equivalence rigidity for any ergodic, essentially free and
measure-preserving action on a standard Borel space with a finite positive
measure of the mapping class group for a compact orientable surface with higher
complexity. We prove similar rigidity results for a finite direct product of
mapping class groups as well.Comment: 11 pages, title changed, a part of contents remove
A new look at C*-simplicity and the unique trace property of a group
We characterize when the reduced C*-algebra of a group has unique tracial
state, respectively, is simple, in terms of Dixmier-type properties of the
group C*-algebra. We also give a simple proof of the recent result by
Breuillard, Kalantar, Kennedy and Ozawa that the reduced C*-algebra of a group
has unique tracial state if and only if the amenable radical of the group is
trivial.Comment: 8 page
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