Understanding the dynamic momentum aperture of the Advanced Light Source

The lifetime of a light source with small emittance like the Advanced Light Source (ALS) is usually limited by the momentum acceptance of the ring. Large momentum acceptances are reached by providing enough RF voltage and by avoiding a degradation of the dynamic momentum aperture. At the ALS the size of the momentum acceptance depends strongly on the transverse dynamics. It is very sensitive to machine conditions such as the tunes and chromaticities since depending on those conditions the Touschek scattered particles explore different resonance regions in the phase space. In this paper we show that by using a single-turn ´pinger´ magnet together with turn-by-turn beam position monitors (BPM) one can identify the cause of a reduction in momentum acceptance and take steps to improve the acceptance