Beam response measurements at SPEAR*

Abstract Two types of beam response measurements were carried out in SPEAR with the aim of gaining understanding of high intensity phenomena. In the first case, the beam was kicked horizontally with the injection kicker magnet and the am-plitude of the resulting betatron oscillation was observed as a function of time. This experiment was carried out for different beam intensities. At large currents, the decay of the oscillation is dominated by the “head-tail damping ” due to the transverse impedance. It shows the expected dependence on the chromatic-ity. At small currents, the decay of the excited betatron oscilla-tion is due mostly to Landau damping. Another series of exper-iments dealt with the longitudinal behaviour of a single bunch..4 network analyser was used to modulate the phase or ampli-tude of the RF voltage and thereby excite dipole or quadrupole synchrotron oscillations. The modulating frequency was swept through the dipole or quadrupole frequency and the beam re