Vacuum system development status for the APS storage ring

The status of the design and fabrication of a prototype sector of the storage ring vacuum system for the Advanced Photon Source (APS) is described. The 26.5-m-long prototype sector is assembled within a full-scale magnet and tunnel mockup to study interspatial component relationships for maintenance, as well as the vacuum system operational performance. Each completed vacuum section is mounted as an integral part of the modular structure that contains the magnets and magnet power supplies on a common base. Unique automatic machine welding designs and techniques are employed in the fabrication of the aluminum vacuum chambers from extrusions. Special chamber bending procedures and measurement checks are used to maintain the required flatness of the inside chamber light gap surfaces. Photoelectron yields due to low-energy photons in the narrow channel gap of the vacuum chamber and their potential effects on the overall outgassing rate are found to be negligible