CERN Accelerating science

Upgrade of the Swiss Light Source for R&D on ultralow vertical emittance
  by Andreas Streun (PSI), Yannis Papaphilippou (CERN), Marica Biagini (INFN)

Fig1: Image of vertical polarized synchrotron light: for an ideal beam of zero emittance, the image would show complete extinction of light in the midplane. Finite midplane intensity allows one to determine the beam size from the "valley to peak" intensity ratio of the image profile. Image credits: TIARA/ Andreas Streun (PSI)

A high resolution beam size monitor has been commissioned at the SLS for verification of vertical emittance values below 1 pm.

The SLS Vertical Emittance Tuning (SVET) Work Package within the TIARA preparatory phase was a collaboration between PSI, CERN, INFN and MAX IV Lab on instruments and methods for establishing an R&D infrastructure on vertical emittance reduction at the SLS storage ring of PSI. The final report was issued at the end of 2013.

Methods have been established to reduce the vertical emittance through re-alignment of the storage ring lattice and through systematic and random optimization of the optics. Values down to 1 pm have been achieved, and values of about 1.5 pm can be set routinely.

A new monitor was built for measurements of very small beam size and has been tested down to a level of 4 μm to date, corresponding to a vertical emittance of about 1.1 pm for the present SLS optics. The measurement is based on an image of vertically polarized synchrotron radiation, see figure beside.

The monitor beam line extends out of the storage ring tunnel in order to provide a large magnification factor and to allow the optical end station to be accessed during operation. A core component of the monitor is a toroidal mirror for wavelength independent focusing, in use since 2014. In 2013 an intermediate configuration composed from a planar mirror and a lens was used.

Monitor fine tuning is in progress, and a new emittance reduction campaign is scheduled. Further studies on intra-beam scattering effects are planned as an application of the ultralow vertical emittance beam.