Abstract
The transverse bunch spectrum and the transverse decoherence/recoherence following an initial bunch offset are important phenomena in synchrotrons and storage rings, and are widely used for beam and lattice measurements. Incoherent shifts of the particles betatron frequency and of the synchrotron frequency modify the transverse spectrum and the bunch decoherence. In this study we analyze the effects of transverse space charge and of the rf nonlinearity on the decoherence signals. The transverse bunch decoherence and the resulting coherent spectra are measured in the SIS18 synchrotron at GSI Darmstadt for different bunch parameters. Particle tracking simulations together with an analytical model are used to describe the modifications in the decoherence signals and in the coherent spectra due to space charge and the rf bucket nonlinearity.
Highlights
Transverse coherent oscillations of bunches induced by a fast kicker magnet are routinely used in synchrotrons or storage rings to measure, for example, the tune or other ring parameters, see e.g. [1]
The transverse bunch decoherence and the resulting coherent spectra are measured in the SIS18 synchrotron at GSI Darmstadt for different bunch parameters
Particle tracking simulations together with an analytical model are used to describe the modifications in the decoherence signals and in the coherent spectra due to space charge and the rf bucket nonlinearity
Summary
Transverse coherent oscillations of bunches induced by a fast kicker magnet are routinely used in synchrotrons or storage rings to measure, for example, the tune or other ring parameters, see e.g. [1]. One has to account for the spread of the synchrotron frequencies Both transverse space charge and nonlinear synchrotron oscillations are important to understand the decoherence signals and transverse spectra. The observed modification of the head-tail spectrum and of the decoherence signal caused by transverse space charge and nonlinear synchrotron oscillations are explained in terms of our theoretical approach. This approach is based on an expansion of an analytical theory for head-tail modes in combination with particle tracking simulations. The space charge tune shifts determined from the transverse spectra are summarized, the role of nonlinear synchrotron motion is demonstrated and transverse bunch decoherence signals measured for different bunch conditions are presented and explained.
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