GSI, Darmstadt
The effect of space charge on the transverse Schottky spectrum of coasting and bunched beams is studied using measurements and simulations together with analytic models. The measurements of transverse Schottky bands from heavy ion beams are performed in the SIS-18 synchrotron at GSI. In addition we analyze the noise spectrum from a particle tracking code with self-consistent space charge. Both results are compared to analytic models for coasting and for bunched beams with space charge. For coasting beams an analytic model based on the transverse dispersion relation with linear space and chromaticity reproduces the characteristic deformation of Schottky bands with increasing space charge, observed in both measurement and simulation. For bunched beams we find good agreement between the observed shifts of synchrotron satellites and a simplified model for head-tail modes with space charge. The relevance of the results for the analysis of transverse beam stability in the presence of space charge is emphasized.
GSI, Darmstadt
The conservation of the longitudinal beam quality through the SIS-18/100 synchrotron chain is of major importance for the FAIR accelerator project as well as for the SIS-18 upgrade. The generation of a short, intense heavy ion bunch at the end of the machine cycle defines a tight budget for the tolerable longitudinal emittance growth. Potential sources of bunch quality degradation are intensity effects and non-adiabatic rf ramps during the rf capture in SIS-18 and during the barrier bucket pre-compression in SIS-100. The time spend on rf manipulations has to be as small as possible in order to maximize the repetition rate. We report about theoretical and experimental studies in SIS-18 of optimized voltage ramps for rf capture into single and double rf buckets, including space charge and beam-loading effects. Further we show that longitudinal space charge can improve the efficiency of rf manipulations. As an example we present an optimized barrier bucket pre-compression scheme for SIS-100.
TEMF, TU Darmstadt, Darmstadt
GSI, Darmstadt
Funding: This work is supported by the GSI.
Beam coupling impedances have been identified as an appropriate quantity to describe collective instabilities caused through beam-induced fields in heavy ion synchrotron accelerators such as the SIS-18 at the planned SIS-100 at the GSI facility. The impedance contributions caused by the multiple types of beamline components need to be determined to serve as input condition for later stability studies. This paper will present an approach exploiting the abilities of commercial FDTD wake codes such as CST PARTICLE STUDIO® for a benchmark problem with cylindrical geometry. Since exact analytical formulae are available, the obtained numerical results will be compared. Special attention is paid towards the representation of the particle beam as the source of the EM fields and conductive losses.