Large electron positron storage ring preinjector vacuum systems: Design and performance

The large electron positron storage ring (LEP) preinjector will provide the particles to be stored in the LEP. It is composed of a high-intensity linear accelerator (linac) providing 200-MeV electrons for the production of positrons, a low-intensity linac (LIL) for the acceleration of electrons and positrons to 600 MeV (LIL), and an electron positron accumulator (EPA) ring to collect dense bunches of electrons and positrons at 600 MeV (EPA). The LIL rf accelerating cavities and waveguides are typical of severely conductance limited vacuum systems with high rf induced gas loads, in which a low hydrocarbon free residual pressure has to be maintained (5 x 10-8 mbar). For the EPA ring, subjected to synchrotron radiation induced gas desorption, considerations of beam lifetime require a base pressure in the 10-9 mbar range, achievable without in situ bakeout in the shortest possible time. The design features with particular emphasis on conceptual choices, cleanliness and special treatments, new hardware, low outgassing achievements, as well as cost and initial performances of these vacuum systems are presented