MEASUREMENT TECHNIQUES TO CHARACTERIZE INSTABILITIES CAUSED BY ELECTRON CLOUDS

Abstract

The study of electron cloud-related instabilities for the CESR-TA project has required developing new automatic and semi-automatic measurement techniques. The dynamics of the interaction of electron clouds with trains of bunches has been studied via three basic observations. Measurements of tune shifts of bunches along a train has been used extensively with the most recent observations permitting the excitation of single bunches within the train to avoid collective train motion from driving the ensemble of bunches. Another technique was developed to detect the coherent self-excited spectrum for each bunch within a train. This method is particularly useful when beam conditions are near the onset of an instability. The third method was designed to study bunches within the train in conditions before there is unstable motion. This is accomplished by separately driving each bunch within the train for several hundred turns and then observing the damping of its coherent motion. These last two techniques have been applied to study both transverse dipole (centroid) and head-tail motion. We report on the observation methods and give examples of typical results.