A transverse beam instability in the PEP-II HER induced by discharges in the vacuum system

Towards the end of Run 5, transverse instability in the High Energy Ring (HER) curtailed the maximum beam current achievable during physics running. Techniques used in tracking down this instability included fast monitoring of background radiation, temperatures and vacuum pressure. In this way, the origin of the instability was localized and inspection of the vacuum system revealed several damaged bellows shields. Replacing these units significantly reduced the incident rate but did not eliminate it fully. After the end of the run, a number of damaged rf seals were found, possibly having caused the remaining incidents of instability. In Run 6, instability has recurred. In this paper we will outline the steps taken to diagnose the issue and compare the different signatures of instabilities we have seen in PEP-II.