Abstracts Brochure - CERN

THPCH — Poster Session 29-Jun-06 16:00 - 18:00
Space Charge Induced Resonance Trapping in High-intensity Synchrotrons
With the recent development of high-intensity
circular accelerators, the simultaneous G. Franchetti, I. Hofmann (GSI)
presence of space charge and lattice nonlinearities
has gained special attention as possible source of beam loss. In this paper we present our understanding of
the role of space charge and synchrotron motion as well as chromaticity for trapping of particles into the islands of
nonlinear reonances. We show that the three effects combined can lead to significant beam loss, where each individual
effect leads to small or negligible loss. We apply our findings to the SIS100 of the FAIR project, where the main
source of field nonlinearities stems from the pulsed super-conducting dipoles, and the beam dynamics challenge is
an extended storage at the injection flat-bottom, over almost one second, together with a relatively large space charge
tune shift.
Considerations for the High-intensity Working Points of the SIS100
In the FAIR project the SIS100 synchrotron
is foreseen to provide high-intensity beams
of U 28+, including slow extraction to the
radioactive beam experimental area, as well
G. Franchetti, O. Boine-Frankenheim, I. Hofmann, V. Kornilov, J.
Stadlmann (GSI) S.-Y. Lee (IUCF)
as high-intensity p beams for the production of antiprotons. In this paper we discuss the proposal of three different
working points, which should serve the different needs: (1) a high intensity working point for U 28+ ; (2) a slow
extraction working point (also U 28+ ); (3) a proton operation working point to avoid transition crossing. The challenging
beam loss control for all three applications requires a careful account of the effects of space charge, lattice nonlinearities
and chromaticity, which will be discussed in detail in this paper. Since tunes are not split by an integer and the injected
emittances are different, the Montague stop-band needs to be avoided. Moreover, final bunch compression for the
U beam requires a sufficiently small momentum spread, and the risk of transverse resisitive wall instabilities poses
further limitations on our choice of working points.
Scaling Laws for the Montague Resonance
The space-charge-driven Montague resonance
is a source of emittance coupling I. Hofmann, G. Franchetti (GSI)
in high-intensity accelerators with un-split
tunes. Here we present scaling laws for the stop-band widths, growth rates and crossing behavior of this fourth order
resonance. Our results on the coupling can be applied to circular machines as well as to linear accelerators. Based
on self-consistent coasting beam simulation we show that for slow crossing of the stop-bands a strong directional
dependence exists: in one direction the exchange is smooth and reversible, in the other direction it is discontinuous.
We also discuss the combined effect of the Montague resonance and linear coupling by skew quadrupoles.
387
THPCH004
THPCH005
THPCH006