First beam commissioning results from the PEP-II B factory high-energy ring: Intensity effects

In two beam commissioning periods, clear evidence for intensity-related effects has been seen at the PEP-II High Energy Ring. In the presence of one unshielded bellows, beam currents appeared limited to about 60 mA and pronounced vertical beam motion was seen, which scraped parts of the beam out of the ring. With all bellows shielded, beam currents up to 300 mA were obtained, limited by a loss of longitudinal control at the highest beam current. Tune shift with intensity was observed, and there is evidence for an increase in bunch motion along an injected bunch train.