20,810 research outputs found
Electron cloud buildup and impedance effects on beam dynamics in the future circular e+eâ collider and experimental characterization of thin TiZrV vacuum chamber coatings
The Future Circular Collider FCC-ee is a study toward a high luminosity electron-positron collider with a centre-of-mass energy from 91 GeV to 365 GeV. Due to the beam parameters and pipe dimensions, collective effects and electron cloud can be very critical aspects for the machine and can represent the main limitations to its performance. An estimation of the electron cloud build up in the main machine components and an impedance model are required to analyze the induced instabilities and to find solutions for their mitigation. Special attention has been given to the resistive wall impedance associated with a layer of nonevaporable getter (NEG) coating on the vacuum chamber required for electron cloud mitigation. The studies presented in this paper will show that minimizing the thickness of this coating layer is mandatory to increase the single bunch instability thresholds in the proposed lepton collider at 45.6 GeV. For this reason, NEG thin films with thicknesses below 250 nm have been investigated by means of numerical simulations to minimize the resistive wall impedance. In parallel, an extensive measurement campaign was performed at CERN to characterize these thin films, with the purpose of finding the minimum effective thickness satisfying vacuum and electron cloud requirements
Soft X-ray reflectivity: from quasi-perfect mirrors to accelerator walls
Reflection of light from surfaces is a very common, but complex phenomenon
not only in science and technology, but in every day life. The underlying basic
optical principles have been developed within the last five centuries using
visible light available from the sun or other laboratory light sources. X-rays
were detected in 1895, and the full potential of soft- and hard-x ray radiation
as a probe for the electronic and geometric properties of matter, for material
analysis and its characterisation is available only since the advent of
synchrotron radiation sources some 50 years ago. On the other hand
high-brilliance and high power synchrotron radiation of present-days 3rd and
4th generation light sources is not always beneficial. Highenergy machines and
accelerator-based light sources can suffer from a serious performance drop or
limitations due to interaction of the synchrotron radiation with the
accelerator walls, thus producing clouds of photoelectrons (e-cloud) which in
turn interact with the accelerated beam. Thus the suitable choice of
accelerator materials and their surface coating, which determines the x-ray
optical behaviour is of utmost importance to achieve ultimate emittance. Basic
optical principles and examples on reflectivity for selected materials are
given here.Comment: 11 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,
Italy; CERN Yellow Report CERN-2013-002, pp.105-11
Accelerator Design for the CHESS-U Upgrade
During the summer and fall of 2018 the Cornell High Energy Synchrotron Source
(CHESS) is undergoing an upgrade to increase high-energy flux for x-ray users.
The upgrade requires replacing one-sixth of the Cornell Electron Storage Ring
(CESR), inverting the polarity of half of the CHESS beam lines, and switching
to single-beam on-axis operation. The new sextant is comprised of six
double-bend achromats (DBAs) with combined-function dipole-quadrupoles.
Although the DBA design is widely utilized and well understood, the constraints
for the CESR modifications make the CHESS-U lattice unique. This paper
describes the design objectives, constraints, and implementation for the CESR
accelerator upgrade for CHESS-U
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