Abstracts Brochure - CERN

THPCH040
THPCH041
THPCH042
THPCH043
29-Jun-06 16:00 - 18:00 THPCH — Poster Session
Linac Focusing and Beam Break Up for 4GLS
As part of the design for 4GLS the linac focus-
E. Wooldridge, B.D. Muratori (CCLRC/DL/ASTeC)
ing and its effect on the beam break up (BBU)
threshold have been studied. The choice of
graded gradient focusing scheme is discussed and initial models of the focusing, using a triplet of quadrupoles
between each of the modules within the linac, are presented. The quadrupoles were set-up in a defocusing - focusing
- defocusing format with strengths of -1/2k, k, -1/2k. Using these models the BBU threshold was computed using
available codes assuming a 9-cell TESLA cavity within the linac and a 7-cell design with HOM dampers. A sweep of
the magnet strength with respect to the BBU threshold showed that there is an optimum setting.
Alternate Cavity Designs to Reduce BBU
An investigation was carried out on alternate
E. Wooldridge (CCLRC/DL/ASTeC)
cavity designs to decrease the effect of the
higher order modes (HOMs) whilst maintaining
the cavity accelerating gradient. The cavities were modelled in Microwave Studio and the number of cells per
cavity and the number of cells per unit length were examined. HOM data from these models was used in beam break
up (BBU) codes to calculate the threshold and the results are presented here. The cells of each cavity were slightly
deformed alternately in the x and y planes so that the fundamental frequency of the cavity remained unperturbed,
whilst minimising the HOM coupling between consecutive cells. Other patterns, such as alternating each deformed
cell by several degrees, were also investigated. The data from these e-m models was also used in BBU calculations
and their thresholds calculated.
Numerical Estimations of Wakefields and Impedances for Diamond Collimators
The storage ring of the Diamond light source
S.A. Pande, R. Bartolini, R. T. Fielder, M. Jensen (Diamond) will use two collimators, one in horizontal
and one in the vertical planes in the injection
straight to protect the IDs from the injection and Touschek losses. These collimators, in the form of tapered metallic
intrusions in to the vacuum chamber, will generate considerable wake fields and will contribute to the overall machine
impedance. In this paper we present the results of ABCI and MAFIA numerical simulations to estimate these effects.
Jitter Studies for the FERMI@ELETTRA Linac
The FEL project FERMI@ELETTRA* will use
P. Craievich, S. Di Mitri (ELETTRA)
the existing linac upgraded to 1.2GeV to produce
photon pulses in the wavelength range
between 100-10 nm by means of harmonic generation in a seeded scheme. FEL operations foresee stringent requirements
for the stability of the global linac output parameters, such as the electron bunch arrival time, peak current,
average energy and the slice electron bunch parameters, such as the slice peak current and slice average energy. In
order to understand the sensitivity of these parameters to jitters of various error sources along the linac an elaborate
study using tracking codes has been performed. As a result, we created a tolerance budget to be used as guidance in
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