Complicated bunch pattern in PEP-II

PEP-II, the asymmetric B-Factory at SLAC, has delivered a luminosity of 3.1/spl middot/10/sup 33/ cm/sup -2/ s/sup -1/. This was achieved with 692 bunches in a basic "by-3" bunch pattern. Many gaps in the bunch train were necessary to suppress a blow-up of the positron beam due to an electron cloud instability (ECI). The actual pattern had 10 bunches in a row (every third bucket), then 6 bunches missing. This 48-bucket long pattern was repeated till the last bucket (3320) before the ion clearing gap. The Low Energy Ring (LER) required an additional modification of the first bunch after each of the gaps. With a smaller spot size due to less ECI blow-up, the charge in these bunches was reduced by 10-20% to avoid kicking out the corresponding High Energy Ring (HER) bunches. A readout error of the charge along the whole train was counteracted with a 20% charge variation at the input. The reasons and developments of these and more complicated bunch patterns are discussed.