Performance of Small‐Gap Undulators at the SLS Intermediate Energy Storage Ring

The Swiss Light Source (SLS) at the Paul Scherrer Institut (PSI) became the first medium energy synchrotron user facility to rely on the high harmonic operation of small gap, short period undulators to extend high brightness radiation into a regime (3–18 keV) otherwise only accessible using lower brightness wigglers or operation at higher electron beam energy. Today several facilities with beam energy 2–3 GeV follow a similar route. A PSI/SPring‐8 collaboration was formed to install and operate the first in‐vacuum undulator shortly after commissioning of the SLS storage ring (2.4 GeV) in 2001. The goal of the joint project was to prove that high harmonic operation of small period undulators at small gaps is a valid concept to operate the PX‐I beamline at 1 A under user operation conditions. The performance of the PX‐I beamline proved to be excellent and launched the installation of meanwhile 4 new in‐vacuum undulators. Having routinely operated such devices for 5 years, our experience confirms that (1) th...