Bunch length control in the NSLS VUV ring

The lifetime in the NSLS VUV ring is limited by intra-bunch scattering (Touschek scattering). A second RF cavity was added to lengthen the electron bunch, thereby reducing the Touschek loss rate. Initially, the cavity was operated in a “passive” mode. This provided significant lifetime enhancement at higher currents, but also created larger than normal bunch length variations over the range of operating currents. In October 1993, a generator was added to the system to provide greater bunch length control and added lifetime at all operating currents. Recent studies have also been done on bunch shortening with encouraging results. This paper provides a summary of the system, including results from studies and operations.