Longitudinal feedback at CESR

Total stored electron and positron beam currents at the Cornell Electron Storage Ring (CESR) have been limited by the presence of a dipole multibunch longitudinal instability having a threshold at approximately 250 mA of total current. A longitudinal feedback system has been under constant development, test, operation and upgrade over the past several years. The result has been an increase in the High Energy Physics operating current to over 500 mA total. This paper describes the overall design of the present system, using a horizontal stripline kicker to produce combined horizontal and longitudinal bunch by bunch beam stabilization. Some details on specific subsystems, including: receiver design, individual bunch phase DC offset correction, digital signal filtering, and the RF modulator will be given, as well as an outline of plans for further development.