Determination of a small vertical electron beam profile and emittance at the Swiss Light Source

We report on the small vertical emittance achieved at the 2.4 GeV Swiss Light Source (SLS). A method utilizing vertically polarized synchrotron radiation (SR), in the visible to ultra-violet (vis–UV) range, has been implemented to determine the vertical electron beam size. The paper describes in detail the beam size measurement method and discusses possible error contributions when deducing the corresponding emittance value. The smallest vertical rms beam size determined to date is σey=(6.4±0.5) μm. For a low emittance tuning, the vertical rms beam emittance at the monitor was determined to be εy=(3.2±0.7) pmrad over a period of several days in 400 mA multi-bunch (0.98 nC/bunch) user top-up operation mode. The corresponding emittance ratio was g=(0.05±0.02)%. The minimization of the vertical emittance was also demonstrated to be of a global nature.