Transverse Decoherence and Coherent Spectra in Long Bunches with Space Charge

TL;DR

This paper investigates how transverse space charge and RF nonlinearity influence decoherence and coherent spectra in long particle bunches, combining measurements, simulations, and analytical modeling.

Contribution

It provides a detailed analysis of the effects of space charge and RF nonlinearity on decoherence signals and spectra in long bunches, supported by experimental and simulation data.

Findings

Space charge modifies the transverse spectrum and decoherence.

RF nonlinearity affects the coherence and spectral features.

Experimental results agree with analytical and simulation models.

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.