Transverse instabilities of coasting beams with space charge

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. The frequencies of the bunch head-tail modes provide a direct measure for the self-field space charge tune shift. 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.

Section: A Longitudinal Dipole Frequencymentioning

confidence: 96%

Transverse decoherence and coherent spectra in long bunches with space charge

Kornilov

2012

“…Balbekov [3] addressed the space charge effect on Landau damping in the weak intensity regime and found a damping rate proportional to the incoherent tune shift and independent of the synchrotron tune, which is similar to our results. However his suggestion of a damping rate decreasing with increasing mode number seems to contradict the typical behavior of Landau damping in physical systems [4][5][6]. The effect of space charge on the modes in bunched beams was also addressed in 1998 by Blaskiewicz [7], who showed that space charge can suppress the fast head-tail instability.…”

Section: Introductionmentioning

confidence: 99%

Simulation of transverse modes with their intrinsic Landau damping for bunched beams in the presence of space charge

Macridin

Burov

Stern

et al. 2015

Transverse dipole modes in bunches with space charge are simulated using the SYNERGIA accelerator modeling package and analyzed with dynamic mode decomposition. The properties of the first three space charge modes, including their shape, damping rates, and tune shifts are described over the entire range of space charge strength. The intrinsic Landau damping predicted and estimated in 2009 by one of the authors is confirmed with a reasonable scaling factor of ≃2.4. For the KV distribution, very good agreement with PATRIC simulations performed by Kornilov and Boine-Frankenheim is obtained.

“…However, the assumed model is arguable because of the assumptions that the beam oscillates rigidly [16] and that the space-charge force is linear. On the other hand.…”

Section: Introductionmentioning

confidence: 99%

Transverse Schottky and beam transfer function measurements in space charge affected coasting ion beams

Paret

Kornilov

Weiland

2010

Transverse Schottky spectra and beam transfer functions (BTFs) of coasting ion beams were measured in the heavy ion synchrotron SIS-18 in order to study the impact of space charge on the transverse beam dynamics. The particle number in the beam was varied to investigate the intensity dependence of the space-charge effect. No cooling was applied to the beams throughout the experiment. The expected deformation of the Schottky spectra and BTFs is observed. An analytic model with linear space charge is employed to describe the deformed Schottky and BTF signals. In this model, the incoherent space-charge force and the coherent forces due to impedances are treated separately. Using the model, the space-charge induced tune shift is evaluated both from the position and the form of the signals. The data are well described by the model, only in the high-intensity BTFs deviations are observed. The stability diagrams are shifted according to the space-charge parameter obtained from the BTFs. In addition, the tune shift is estimated by virtue of measured beam profiles and particle numbers. The estimated tune shift is of the same order of magnitude but smaller than the measured one. Possible explanations for deviations between the measurements, the model, and the estimation are discussed.