Lifetime studies at the Advanced Light Source

The Advanced Light Source (ALS), operated at the Lawrence Berkeley National Laboratory, is a third generation synchrotron light source optimized for high brightness synchrotron radiation in the VUV and soft x-ray regime. The storage ring is designed as a low emittance storage ring and operates at energies of 1.5 GeV or 1.9 GeV, storing 400 mA in approximately 300 bunches. The nominal horizontal emittance at 1.5 GeV is 3:5 nm rad, with an emittance coupling of 1% achieved so far. The nominal bunch length is s 5 mm. Multi-bunch feedback systems control transverse and longitudinal multi-bunch instabilities, thus keeping the beam size small even for high multi-bunch currents. The lifetime in the ALS is one of the most important operational parameters. Longer lifetimes are favorable out of several reasons: longer time spans to set up and run experiments, less thermal variations of the vacuum chamber and beam line optics components, and more photons for the experimenters. The lifetime in an electron storage ring is usually determined by the following effects: quantum excitation ( q), elastic ( el) and inelastic scattering ( inel) on the residual gas atoms, scattering of electrons within the bunch (Touschek-effect) ( tou), and trapping of charged particles in the beam potential ( ion). The total lifetime becomes: