Vacuum performance and beam life time in the PEP II storage rings

The vacuum systems of the storage rings of the PEP-II B-Factory have had by now over two years of production running at high beam current and seen synchrotron radiation from almost 4 kAh (High Energy Ring) and 10 kAh (Low Energy Ring) of integrated beam current. The systems have performed well, reaching the design pressures and being able to cope with beam currents of almost 1 A (HER) and in excess of 2 A (LER). The photo-desorption coefficient /spl eta/ was found in the HER to have reached values as low as 10/sup -7/. The shielded bellows have performed very well, with only one pair of bellows assemblies damaged due to higher-order mode generation from a known, nearby source. Issues encountered during normal operation have been a significant amount of dust trapping in the HER and the effect of a cloud of photo-electrons around the positron beam affecting the LER beam size. A couple of chambers in the HER failed; these failures arose from a combination of design and fabrication issues. The beam life time in the LER has been lower than expected based on the vacuum pressure and has been determined to be Touschek limited.