Feedback for suppression of single-bunch transverse instability in electron-positron storage rings

Transverse head-tail instability is a severe limitation of a single-bunch beam current in circular accelerators. Applicability and efficiency of feedbacks for suppression of the instability is analyzed. Both chromatic and nonlinear effects have been taken into account to understand the processes of excitation and damping of the instability. Analytical estimations are compared with the results of experiments and numerical simulations. A feedback system has been developed, installed and commissioned at the VEPP-4M electron-positron collider. An original scheme of the kicker powering has been developed to provide the necessary performance with minimal expenses. Real-time digital data processing performed by a code running in an FPGA module provides high efficiency and flexibility of the system. During the system commissioning, a more than threefold increase of intensity of the VEPP-4M single-bunch beam has been achieved.