Effects of space charge and reactive wall impedance on bunched beams

Space charge and reactive wall impedance create longitudinal forces inside the bunch which change the incoherent phase oscillation frequency, the bunch length and the size of the RF-bucket. These effects have been investigated with bunched beams in the ISR. By measuring the shift of the quadrupole mode phase oscillation frequency, the strength of the self-forces was determined. The inductive wall is dominant and its impedance (divided by the mode number) was measured to be mod Z mod /n approximately=26 Ohms. An increase of bunch length with current was measured. The reduction of the bucket size affects the stacking process. By correcting for it, an increased density of the stacked beam was achieved. (14 refs).