Abstracts Brochure - CERN

THPCH075
THPCH076
THPCH077
29-Jun-06 16:00 - 18:00 THPCH — Poster Session
effect, etc. Unfortunately, over the wavelengths of interest, data in the literature on the electrical properties of metals
such as Cu and Al is sparse. In this report, we present recent reflectivity measurements performed at Brookhaven
National Laboratory on Cu and Al samples. This data is compared with theory and the implication for the LCLS
performance is discussed.
Simulation of the Electron Cloud for Various Configurations of a Damping Ring for the
ILC
M.T.F. Pivi, L. Wang (SLAC) K. Ohmi (KEK) R. Wanzenberg (DESY)
A. Wolski (Liverpool University, Science Faculty) F. Zimmermann
(CERN)
408
In the beam pipe of the Damping Ring (DR)
of the International Linear Collider (ILC), an
electron cloud may be first produced by photoelectrons
and ionization of residual gasses
and then increased by the secondary emis-
sion process. This paper reports about the work that has been done by the electron cloud assessment international
task force group for the recommendation of the ILC Damping Rings baseline design, made in November 2005. We
have carefully estimated the secondary electron yield (SEY) threshold for electron cloud build-up and estimated the
related single − and coupled-bunch instabilities that can be caused by the presence of electron cloud as a function of
beam current and surface properties, for a variety of optics designs. The result of these studies was an important consideration
in the choice of a 6-km design for the ILC damping rings. On the basis of the theoretical and experimental
work, the baseline configuration specifies a pair of damping rings for the positron beam to mitigate the effects of the
electron cloud.
Resistive Wall Wake Effect of a Grooved Vacuum Chamber
To suppress the emission of secondary elec-
G.V. Stupakov, K.L.F. Bane (SLAC)
trons in accelerators with positively charged
beams (ions or positrons) it has been proposed
to use a vacuum chamber that is longitudinally grooved (or, equivalently, one can say finned)*/**. One
consequence of having such a chamber in an accelerator is an increased resistive wall impedance. In this paper, we
calculate the resistive wall impedance of one such finned chamber, planned to be used in experimental studies of
secondary emission suppression at SLAC. For rectangular fins, we use an analytical method based on a conformal
mapping approach; we compare the results with a numerical solution of the field equation. We also numerically
compute the impedance for rounded fins (as will be used in the SLAC experiment) and analyse how the impedance
depends on geometric properties of the fins.
*A. A. Krasnov. Vaccum, vol. 73, p. 195, (2004).**G. Stupakov and M. Pivi. Preprint SLAC-TN-04-045, (2004).
Bunch Train Instabilities in the Damping Rings of the ILC
In the damping ring of the International Lin-
L. Wang (SLAC)
ear Collider (ILC), variation in the bunch
train fill pattern is a good remedy to clear
the trapped ions in the electron ring and reduce the electron cloud density in the positron ring. This paper investigates
the coupled bunch instabilities due to different sources of wake field in the ILC damping ring with a bunch
train fill pattern.