Creating a pseudo single bunch at the ALS

Abstract

Typically storage ring light sources operate with the maximum number of bunches as possible with a gap for ion clearing. By evenly distributing the beam current the overall beam lifetime is maximized. The Advanced Light Source (ALS) has 2 nanoseconds between the bunches and typically operates with 276 bunches out of a possible 328. For experimenters doing timing experiment this bunch separation is too small and would prefer to see only one or two bunches in the ring. The ALS allocates four weeks every year for dedicated 2-bunch operation. In order to provide more flexible operations and substantially increase the amount of operating time for time-of-flight experimenters, it is being proposed to kick one bunch on a different vertical closed orbit. By spatially separating the light from this bunch from the main bunch train in the beamline, one could potentially have single bunch operation all year round. By putting this bunch in the middle of the ion clearing gap the required bandwidth of the kicker magnets is reduced. Using one kicker magnet running at the ring repetition rate (1.5 MHz), this bunch could be permanently put on a different closed orbit. Using multiple kicker magnets, this bunch could be locally offset at an arbitrary frequency.

Transverse multibunch instabilities for two bunch trains on separated orbits

“…It has been reported in [1,2] that a camshaft bunch can be produced by a fast kicker at the repetition rate of the revolution frequency of the storage ring at the Advanced Light Source (ALS). The camshaft bunch in the ALS storage ring permanently stays on the distorted orbit so that the radiation is separated from that of the bunch train and can be used for time-of-flight experiments.…”