Abstracts Brochure - CERN

WEPCH — Poster Session 28-Jun-06 16:00 - 18:00
works with external focusing, but would be very effective in a plasma ion focusing channel where the density of ions
is simply increased as one goes down the channel. In the original work (Ref 1) motion of the ions was not included
(as it was assumed to be a small effect). Recently, it has been suggested that ion motion in an adiabatic focuser would
be significant and, even, preclude operation of the focuser as previously envisioned**. In this paper we numerically
study the ion motion in the focuser. The ions clearly influence each other and, most importantly, are influenced by
the electric field of the electrons being focused. It is shown that parameters can be selected such that the adiabatic
focuser works as well as originally envisioned.
*P. Chen et al. Phys. Rev. Lett. 64, 1231 (1990).**J. R. Rosenzweig, et al. Phys. Rev. Lett. 95, 195002 (2005).
Studies of the Nonlinear Dynamics Effects of APPLE-II Type EPUs at the ALS
Elliptically Polarizing Undulators (EPUs)
have become more and more popular at synchrotron
radiation sources, providing full
polarization control of the photon beam. The
C. Steier, S. Marks, S. Prestemon, D. Robin, D. Schlueter, W. Wan
(LBNL)
fields of the most commonly used APPLE-II type EPUs have a very fast, intrinsic field roll-off, creating significant nonlinearities
of the beam motion with in some cases large impact on the dynamic (momentum) aperture. In general, the
nonlinear effects get stronger with longer periods and higher undulator magnetic fields. One of the planned future
beamlines at the ALS (MERLIN) will use a quasiperiodic EPU with 9 cm period and maximum B fields of about 1.3 T.
We will present simulation studies for the proposed shimming schemes for this future device to reduce the nonlinear
effects to acceptable values, as well as experimental studies for the existing 5 cm period EPUs already installed in the
ALS.
Ion Effects in the Electron Damping Ring of the International Linear Collider
Ion induced beam instability and tune shift
are critical issues for the electron damp- L. Wang, T.O. Raubenheimer (SLAC) A. Wolski (LBNL)
ing ring of the International Linear Collider
(ILC). To avoid conventional ion trapping, gaps are introduced in the electron beam by missing bunches in a train of
bunches. However, the beam can still suffer from the fast ion instability (FII) driven by ions that last only for a single
passage of the electron beam and are not trapped for multiple turns. Our study shows that the ion effects can be
significantly mitigated by using multiple gaps, so that the stored beam consists of a number of relatively short bunch
trains. Another way to avoid trapped ions is to introduce clearing electrodes. The ion effects in the ILC damping
rings are investigated using both analytical and numerical methods.
Observation of the Long-range Beam-beam Effect in RHIC and Plans for Compensation
At large distances the electromagnetic field
of a wire is the same as the field produced by
a bunch. Such a long-range beam-beam wire
compensator was proposed for the LHC, and
W. Fischer (BNL) U. Dorda, J.-P. Koutchouk, F. Zimmermann
(CERN) J. Qiang (LBNL) T. Sen (Fermilab) J. Shi (KU)
single beam tests with wire compensators were successfully done in the SPS. RHIC offers the possibility to test the
compensation scheme with colliding beams. We report on measurements of beam loss measurements as a function of
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