GSI, Darmstadt
Transverse bunch offsets typically occur after bunch-to-bucket transfer between synchrotrons. Decoherence of the oscillations can cause emittance growth and beam loss, which should be avoided in high-intensity synchrotrons, like the projected SIS-100 synchrotron of the FAIR project. In this contribution we investigate how space charge and impedances modify the bunch decoherence and associated diagnostics methods as turn-by-turn chromaticity measurements. Results of machine experiments at the SIS18 synchrotron are compared with particle tracking simulations.
GSI, Darmstadt
TEMF, TU Darmstadt, Darmstadt
A study of the transverse dynamics of coasting ion beams with moderate space charge is presented. An analytic model based on the dispersion relation with a linear space-charge force is used to describe the impact of space charge on transverse beam transfer functions (BTFs) and the stability limits of a beam. The dielectric function obtained in this way is employed to describe the transverse Schottky spectrum with linear space charge as well. The difference between space charge and impedance effects is highlighted. An experiment performed in the heavy ion synchrotron SIS-18 at GSI to detect space-charge effects at different beam intensities is explicated. The measured transverse Schottky spectra, BTFs and stability diagrams are compared with the analytic model. The space-charge parameters evaluated from the Schottky and BTF measurements are compared with estimations based on measured beam parameters. Furthermore, particle tracking simulations demonstrating the impact of collective effects on the Schottky and BTF diagnostics are presented. The simulation results are used to verify the space-charge model.
GSI, Darmstadt
Significant progress has been made recently in the understanding of the effects of direct space charge on the transverse head-tail bunch dynamics. Different analytic approaches for head-tail modes in bunches for different space-charge parameter regimes have been suggested. Besides head-tail eigenmode characteristics, Landau damping in a bunch exclusively due to space charge has been predicted. In this contribution we compare results of particle tracking simulations with theoretical predictions for the eigenfrequencies and eigenfunctions of head-tail modes in a Gaussian bunch. We demonstrate the space-charge induced Landau damping in a bunch and quantify damping rates for different modes and space-charge tune shifts. Under conditions below the mode coupling threshold we study the head-tail instability with space charge. Our results show that the space-charge induced damping can suppress the instability for moderately strong space charge. For strong space charge the instability growth rates asymptotically reach constant vales, in agreement with theoretical predictions.