SURF-II Upgrade Features Magnet and RF System Enhancements

The NBS electron storage ring, SURF-II, has been upgraded with a number of major enhancements. The magnet system capability has been increased from 240 to 300 MeV, although actual operation is presently RF limited to 280 MeV. The storage ring magnet has been carefully mapped, resulting in more precise determination of beam energy and better radiometric data. The RF system has been augmented by an auxiliary second harmonic system, terminating in a novel, dual purpose cavity. This structure performs the function of the bump coil during injection, while during acceleration and stored beam operation it functions as a second harmonic cavity. In the latter mode it can either be tuned passively to suppress longitudinal bunch oscillations, or it can be driven actively to modify the longitudinal bunch shape. With proper amplitude and phasing relative to the main RF cavity, bunch lengthening can be achieved, resulting in improved beam life-time without an increase in vertical size.