Status of the PEP-II low-energy ring vacuum system

The PEP-II B Factory Low-Energy Ring (LER) will operate at 3.1 GeV with 2.1 A; design specifications are based on 3.5 GeV at 3 A. The vacuum system, 2200 m long, consists of 6 arcs and 6 straights. The arc vacuum system is based on an aluminum antechamber pumped by titanium sublimators located directly under discrete photon stops, supplemented by 110 1/s ion pumps near the end of each dipole. The straight sections serve various utility functions, including emittance control with a wiggler, injection, and an interaction region (IR). Vacuum chambers in most of the straight sections are circular stainless steel pipe with external copper plating to facilitate heat transfer to cooling tubes brazed to the outside wall. The wiggler chicane vacuum system uses both aluminum and stainless steel technology, along with a 24 m long distributed copper photon dump. The IR vacuum system is mainly based on copper extrusions. LER vacuum system components are either in the late stage of prototyping or already in full production.