The Damper for the Transverse Instabilities of the SPS

For beam intensities above 1012 protons per pulse in the SPS, collective transverse beam instabilities develop with frequencies between 15 kHz and 3 MHz because of the resistive wall effect of the vacuum chamber1). An active feedback system2) with an electrostatic deflector has been installed in the SPS for damping the resistive wall instabilities in both the vertical and horizontal planes. Measurements have been made to determine the threshold and growth rate of these instabilities. As a novel application, the damper can be used also for the excitation of small coherent betatron oscillations. A phase-locked loop tracks the beam oscillations and provides a continuous display of the betatron wavenumber Q during the cycle.