Abstracts Brochure - CERN

THPCH034
THPCH035
THPCH036
29-Jun-06 16:00 - 18:00 THPCH — Poster Session
Transverse Coupling Impedance in a Smooth Resistive Cylindrical Pipe for Arbitrary
Beam Energies
A.M. Al-Khateeb, O. Boine-Frankenheim, R.W. Hasse, I. Hofmann
(GSI)
396
The transverse coupling impedance is investigated
analytically. For an off-axis motion of
the beam, the perturbed charge distribution
of the beam becomes a function of the az-
imuthal angle, resulting to first order in the beam displacement in a dipole term which is the source of the transverse
impedance. All six components of the electromagnetic field are different from zero and, therefore, both TM and TE
modes will be excited in the beam-pipe and coupled to the beam at the inner surface of the resistive wall. Using
the dipole source term, a linear combination of TM and TE modes is used to get closed form expressions for the
transverse electromagnetic field components excited in the beam-pipe, and a generalized analytic expression for the
corresponding transverse coupling impedance. It has been found that the contributions of the TM and the TE modes
to the real part of the transverse resistive-wall impedance have similar dependence on the relativistic parameter but
with opposite signs, the sum of both always being positive. Some approximate simple formulas for three important
regions corresponding to small, intermediate and large frequencies in the ultrarelativistic limit were also obtained
analytically.
Characterisation of the EU-HOM-damped Normal Conducting 500 MHz Cavity from the
Beam Power Spectrum at DELTA
R.G. Heine, P. Hartmann, T. Weis (DELTA) F. Marhauser, E.
Weihreter (BESSY GmbH)
A HOM-damped prototype cavity developed
in the framework of an EC collaboration has
been installed in the Dortmund synchrotron
light source DELTA. This paper reports on
beam studies performed at beam energies of 1.5 GeV and 542 MeV in an attempt to get information on coupled bunch
instability thresholds. In addition an evaluation of the longitudinal cavity impedance is presented, based on beam
power spectra up to 3 GHz for different filling patterns of the storage ring by analysing the RF signal from the HOMdampers.
Wakefield Calculation of 3D Collimators
The wakefield effects of the collimators is
I. Zagorodnov (DESY) K.L.F. Bane (SLAC)
of concern for future projects. To relax the
wakefield effects a gradual transition from a
large to a small aperture is used. The impedance of a smooth round collimator is understood well and a good agreement
between measurements, theory and simulations is achieved. However, for rectangular flat collimators there is
noticeable difference between theory and experiment. Using recently developed time domain numerical approach,
which is able to model curved boundaries and does not suffer from dispersion in longitudinal direction, we calculate
the short-range geometric wakefields of 3D collimators. This method together with developed by us recently indirect
3D integration algorithm allows to obtain accurate numerical estimations, which are compared to measurements and
to analytical results. The applicability range for the analytical formulas is highlighted.